Refactor CommandResolver into individual CommandResolver Implementation

classes.

Write Unit Tests covering Composite DefaultCommandResolver and
ScriptCommandResolver.

baseline

Baseline2

src/Microsoft.DotNet.Cli.Utils/CommandResolution/AbstractPathBasedCommandResolver.cs

@@ -0,0 +1,60 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public abstract class AbstractPathBasedCommandResolver : ICommandResolver
+    {
+        protected IEnvironmentProvider _environment;
+        protected IPlatformCommandSpecFactory _commandSpecFactory;
+
+        public AbstractPathBasedCommandResolver(IEnvironmentProvider environment, 
+            IPlatformCommandSpecFactory commandSpecFactory)
+        {
+            if (environment == null)
+            {
+                throw new ArgumentNullException("environment");
+            }
+
+            if (commandSpecFactory == null)
+            {
+                throw new ArgumentNullException("commandSpecFactory");
+            }
+
+            _environment = environment;
+            _commandSpecFactory = commandSpecFactory;
+        }
+
+        public CommandSpec Resolve(CommandResolverArguments commandResolverArguments)
+        {
+            if (commandResolverArguments.CommandName == null)
+            {
+                return null;
+            }
+
+            var commandPath = ResolveCommandPath(commandResolverArguments);
+
+            if (commandPath == null)
+            {
+                return null;
+            }
+
+            return _commandSpecFactory.CreateCommandSpec(
+                    commandResolverArguments.CommandName,
+                    commandResolverArguments.CommandArguments.EmptyIfNull(),
+                    commandPath,
+                    GetCommandResolutionStrategy(),
+                    _environment);
+        }
+
+        internal abstract string ResolveCommandPath(CommandResolverArguments commandResolverArguments);
+        internal abstract CommandResolutionStrategy GetCommandResolutionStrategy();
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/AppBaseCommandResolver.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class AppBaseCommandResolver : AbstractPathBasedCommandResolver
+    {
+        public AppBaseCommandResolver(IEnvironmentProvider environment, 
+            IPlatformCommandSpecFactory commandSpecFactory) : base(environment, commandSpecFactory) { }
+
+        internal override string ResolveCommandPath(CommandResolverArguments commandResolverArguments)
+        {
+            return _environment.GetCommandPathFromRootPath(
+                PlatformServices.Default.Application.ApplicationBasePath, 
+                commandResolverArguments.CommandName);
+        }
+
+        internal override CommandResolutionStrategy GetCommandResolutionStrategy()
+        {
+            return CommandResolutionStrategy.BaseDirectory;
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/CommandResolutionStrategy.cs

@@ -0,0 +1,26 @@
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public enum CommandResolutionStrategy
+    {
+        // command loaded from project dependencies nuget package
+        ProjectDependenciesPackage,
+
+        // command loaded from project tools nuget package
+        ProjectToolsPackage,
+
+        // command loaded from the same directory as the executing assembly
+        BaseDirectory,
+
+        // command loaded from the same directory as a project.json file
+        ProjectLocal,
+
+        // command loaded from PATH environment variable
+        Path,
+
+        // command loaded from rooted path
+        RootedPath,
+
+        // command not found
+        None
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/CommandResolverArguments.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using NuGet.Frameworks;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class CommandResolverArguments
+    {
+        public string CommandName { get; set; }
+
+        public IEnumerable<string> CommandArguments { get; set; }
+
+        public NuGetFramework Framework { get; set; }
+
+        public string ProjectDirectory { get; set; }
+
+        public string Configuration { get; set; }
+
+        public IEnumerable<string> InferredExtensions { get; set; }
+
+        public IEnvironmentProvider Environment { get; set; }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/CompositeCommandResolver.cs

@@ -0,0 +1,51 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class CompositeCommandResolver : ICommandResolver
+    {
+        private IList<ICommandResolver> _orderedCommandResolvers;
+
+        public IEnumerable<ICommandResolver> OrderedCommandResolvers 
+        {
+            get 
+            {
+                return _orderedCommandResolvers;
+            }
+        }
+
+        public CompositeCommandResolver()
+        {
+            _orderedCommandResolvers = new List<ICommandResolver>();
+        }
+
+        public void AddCommandResolver(ICommandResolver commandResolver)
+        {
+            _orderedCommandResolvers.Add(commandResolver);
+        }
+        
+        public CommandSpec Resolve(CommandResolverArguments commandResolverArguments)
+        {
+            foreach (var commandResolver in _orderedCommandResolvers)
+            {
+                var commandSpec = commandResolver.Resolve(commandResolverArguments);
+
+                if (commandSpec != null)
+                {
+                    return commandSpec;
+                }
+            }
+
+            return null;
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/DefaultCommandResolver.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class DefaultCommandResolver : CompositeCommandResolver
+    {
+        public static DefaultCommandResolver Create()
+        {
+            var environment = new EnvironmentProvider();
+            var packagedCommandSpecFactory = new PackagedCommandSpecFactory();
+
+            var platformCommandSpecFactory = default(IPlatformCommandSpecFactory);
+            if (PlatformServices.Default.Runtime.OperatingSystemPlatform == Platform.Windows)
+            {
+                platformCommandSpecFactory = new WindowsExePreferredCommandSpecFactory();
+            }
+            else
+            {
+                platformCommandSpecFactory = new GenericPlatformCommandSpecFactory();
+            }
+
+            return new DefaultCommandResolver(environment, packagedCommandSpecFactory, platformCommandSpecFactory);
+        }
+
+        public DefaultCommandResolver(
+            IEnvironmentProvider environment,
+            IPackagedCommandSpecFactory packagedCommandSpecFactory,
+            IPlatformCommandSpecFactory platformCommandSpecFactory) : base()
+        {
+            AddCommandResolver(new RootedCommandResolver());
+            AddCommandResolver(new ProjectDependenciesCommandResolver(environment, packagedCommandSpecFactory));
+            AddCommandResolver(new ProjectToolsCommandResolver(packagedCommandSpecFactory));
+            AddCommandResolver(new AppBaseCommandResolver(environment, platformCommandSpecFactory));
+            AddCommandResolver(new PathCommandResolver(environment, platformCommandSpecFactory));
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/GenericPlatformCommandSpecFactory.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class GenericPlatformCommandSpecFactory : IPlatformCommandSpecFactory
+    {
+        public CommandSpec CreateCommandSpec(
+           string commandName,
+           IEnumerable<string> args,
+           string commandPath,
+           CommandResolutionStrategy resolutionStrategy,
+           IEnvironmentProvider environment)
+        {
+            var escapedArgs = ArgumentEscaper.EscapeAndConcatenateArgArrayForProcessStart(args);
+            return new CommandSpec(commandPath, escapedArgs, resolutionStrategy);
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/ICommandResolver.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public interface ICommandResolver
+    {
+        CommandSpec Resolve(CommandResolverArguments arguments);
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/IPackagedCommandSpecFactory.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.DotNet.ProjectModel.Graph;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public interface IPackagedCommandSpecFactory
+    {
+        CommandSpec CreateCommandSpecFromLibrary(
+            LockFilePackageLibrary library,
+            string commandName,
+            IEnumerable<string> commandArguments,
+            IEnumerable<string> allowedExtensions,
+            string nugetPackagesRoot,
+            CommandResolutionStrategy commandResolutionStrategy,
+            string depsFilePath);
+        
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/IPlatformCommandSpecFactory.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public interface IPlatformCommandSpecFactory
+    {
+        CommandSpec CreateCommandSpec(
+           string commandName,
+           IEnumerable<string> args,
+           string commandPath,
+           CommandResolutionStrategy resolutionStrategy,
+           IEnvironmentProvider environment);
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/PackagedCommandSpecFactory.cs

@@ -0,0 +1,119 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class PackagedCommandSpecFactory : IPackagedCommandSpecFactory
+    {
+        public CommandSpec CreateCommandSpecFromLibrary(
+            LockFilePackageLibrary library,
+            string commandName,
+            IEnumerable<string> commandArguments,
+            IEnumerable<string> allowedExtensions,
+            string nugetPackagesRoot,
+            CommandResolutionStrategy commandResolutionStrategy,
+            string depsFilePath)
+        {
+            var packageDirectory = GetPackageDirectoryFullPath(library, nugetPackagesRoot);
+
+            if (!Directory.Exists(packageDirectory))
+            {
+                return null;
+            }
+
+            var commandFile = GetCommandFileRelativePath(library, commandName, allowedExtensions);
+
+            if (commandFile == null)
+            {
+                return null;
+            }
+
+            var commandPath = Path.Combine(packageDirectory, commandFile);
+
+            return CreateCommandSpecWrappingWithCorehostfDll(
+                commandPath, 
+                commandArguments, 
+                depsFilePath, 
+                commandResolutionStrategy);
+        }
+
+        private string GetPackageDirectoryFullPath(LockFilePackageLibrary library, string nugetPackagesRoot)
+        {
+            var packageDirectory = new VersionFolderPathResolver(nugetPackagesRoot)
+                .GetInstallPath(library.Name, library.Version);
+
+            return packageDirectory;
+        }
+
+        private string GetCommandFileRelativePath(
+            LockFilePackageLibrary library, 
+            string commandName, 
+            IEnumerable<string> allowedExtensions)
+        {
+            // TODO: Should command names be case sensitive?
+            return library.Files
+                    .Where(f => Path.GetFileNameWithoutExtension(f) == commandName)
+                    .Where(e => allowedExtensions.Contains(Path.GetExtension(e)))
+                    .FirstOrDefault();
+        }
+
+        private CommandSpec CreateCommandSpecWrappingWithCorehostfDll(
+            string commandPath, 
+            IEnumerable<string> commandArguments, 
+            string depsFilePath,
+            CommandResolutionStrategy commandResolutionStrategy)
+        {
+            var commandExtension = Path.GetExtension(commandPath);
+
+            if (commandExtension == FileNameSuffixes.DotNet.DynamicLib)
+            {
+                return CreatePackageCommandSpecUsingCorehost(
+                    commandPath, 
+                    commandArguments, 
+                    depsFilePath, 
+                    commandResolutionStrategy);
+            }
+            
+            return CreateCommandSpec(commandPath, commandArguments, commandResolutionStrategy);
+        }
+
+        private CommandSpec CreatePackageCommandSpecUsingCorehost(
+            string commandPath, 
+            IEnumerable<string> commandArguments, 
+            string depsFilePath,
+            CommandResolutionStrategy commandResolutionStrategy)
+        {
+            var corehost = CoreHost.HostExePath;
+
+            var arguments = new List<string>();
+            arguments.Add(commandPath);
+
+            if (depsFilePath != null)
+            {
+                arguments.Add($"--depsfile:{depsFilePath}");
+            }
+
+            arguments.AddRange(commandArguments);
+
+            return CreateCommandSpec(corehost, arguments, commandResolutionStrategy);
+        }
+
+        private CommandSpec CreateCommandSpec(
+            string commandPath, 
+            IEnumerable<string> commandArguments,
+            CommandResolutionStrategy commandResolutionStrategy)
+        {
+            var escapedArgs = ArgumentEscaper.EscapeAndConcatenateArgArrayForProcessStart(commandArguments);
+
+            return new CommandSpec(commandPath, escapedArgs, commandResolutionStrategy);
+        }   
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/PathCommandResolver.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class PathCommandResolver : AbstractPathBasedCommandResolver
+    {
+        public PathCommandResolver(IEnvironmentProvider environment, 
+            IPlatformCommandSpecFactory commandSpecFactory) : base(environment, commandSpecFactory) { }
+
+        internal override string ResolveCommandPath(CommandResolverArguments commandResolverArguments)
+        {
+            return _environment.GetCommandPath(commandResolverArguments.CommandName);
+        }
+
+        internal override CommandResolutionStrategy GetCommandResolutionStrategy()
+        {
+            return CommandResolutionStrategy.Path;
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/ProjectDependenciesCommandResolver.cs

@@ -0,0 +1,179 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class ProjectDependenciesCommandResolver : ICommandResolver
+    {
+        private static readonly CommandResolutionStrategy s_commandResolutionStrategy = 
+            CommandResolutionStrategy.ProjectDependenciesPackage;
+
+        private IEnvironmentProvider _environment;
+        private IPackagedCommandSpecFactory _packagedCommandSpecFactory;
+
+        public ProjectDependenciesCommandResolver(
+            IEnvironmentProvider environment,
+            IPackagedCommandSpecFactory packagedCommandSpecFactory)
+        {
+            if (environment == null)
+            {
+                throw new ArgumentNullException("environment");
+            }
+
+            if (packagedCommandSpecFactory == null)
+            {
+                throw new ArgumentNullException("packagedCommandSpecFactory");
+            }
+
+            _environment = environment;
+            _packagedCommandSpecFactory = packagedCommandSpecFactory;
+        }
+
+        public CommandSpec Resolve(CommandResolverArguments commandResolverArguments)
+        {
+            if (commandResolverArguments.Framework == null 
+                || commandResolverArguments.ProjectDirectory == null
+                || commandResolverArguments.Configuration == null
+                || commandResolverArguments.CommandName == null)
+            {
+                return null;
+            }
+
+            return ResolveFromProjectDependencies(
+                    commandResolverArguments.ProjectDirectory,
+                    commandResolverArguments.Framework,
+                    commandResolverArguments.Configuration,
+                    commandResolverArguments.CommandName,
+                    commandResolverArguments.CommandArguments);
+        }
+
+        private CommandSpec ResolveFromProjectDependencies(
+            string projectDirectory,
+            NuGetFramework framework,
+            string configuration,
+            string commandName,
+            IEnumerable<string> commandArguments)
+        {
+            var allowedExtensions = GetAllowedCommandExtensionsFromEnvironment(_environment);
+
+            var projectContext = GetProjectContextFromDirectory(
+                projectDirectory, 
+                framework);
+
+            if (projectContext == null)
+            { 
+                return null;
+            }
+
+            var depsFilePath = projectContext.GetOutputPaths(configuration).RuntimeFiles.Deps;
+
+            var dependencyLibraries = GetAllDependencyLibraries(projectContext);
+             
+            return ResolveFromDependencyLibraries(
+                dependencyLibraries,
+                depsFilePath,
+                commandName,
+                allowedExtensions,
+                commandArguments,
+                projectContext);
+        }
+
+        private CommandSpec ResolveFromDependencyLibraries(
+            IEnumerable<LockFilePackageLibrary> dependencyLibraries,
+            string depsFilePath,
+            string commandName,
+            IEnumerable<string> allowedExtensions,
+            IEnumerable<string> commandArguments,
+            ProjectContext projectContext)
+        {
+            foreach (var dependencyLibrary in dependencyLibraries)
+            {
+                var commandSpec = ResolveFromDependencyLibrary(
+                    dependencyLibrary,
+                    depsFilePath,
+                    commandName,
+                    allowedExtensions,
+                    commandArguments,
+                    projectContext);
+
+                if (commandSpec != null)
+                {
+                    return commandSpec;
+                }
+            }
+
+            return null;
+        }
+
+        private CommandSpec ResolveFromDependencyLibrary(
+            LockFilePackageLibrary dependencyLibrary,
+            string depsFilePath,
+            string commandName,
+            IEnumerable<string> allowedExtensions,
+            IEnumerable<string> commandArguments,
+            ProjectContext projectContext)
+        {
+            return _packagedCommandSpecFactory.CreateCommandSpecFromLibrary(
+                        dependencyLibrary,
+                        commandName,
+                        commandArguments,
+                        allowedExtensions,
+                        projectContext.PackagesDirectory,
+                        s_commandResolutionStrategy,
+                        depsFilePath);
+        }
+
+        private IEnumerable<LockFilePackageLibrary> GetAllDependencyLibraries(
+            ProjectContext projectContext)
+        {
+            return projectContext.LibraryManager.GetLibraries()
+                .Where(l => l.GetType() == typeof(PackageDescription))
+                .Select(l => l as PackageDescription)
+                .Select(p => p.Library);
+        }
+
+        private ProjectContext GetProjectContextFromDirectory(string directory, NuGetFramework framework)
+        {
+            if (directory == null || framework == null)
+            {
+                return null;
+            }
+
+            var projectRootPath = directory;
+
+            if (!File.Exists(Path.Combine(projectRootPath, Project.FileName)))
+            {
+                return null;
+            }
+
+            var projectContext = ProjectContext.Create(
+                projectRootPath, 
+                framework, 
+                PlatformServices.Default.Runtime.GetAllCandidateRuntimeIdentifiers());
+
+            if (projectContext.RuntimeIdentifier == null)
+            {
+                return null;
+            }
+
+            return projectContext;
+        }
+
+        private IEnumerable<string> GetAllowedCommandExtensionsFromEnvironment(IEnvironmentProvider environment)
+        {
+            var allowedCommandExtensions = new List<string>();
+            allowedCommandExtensions.AddRange(environment.ExecutableExtensions);
+            allowedCommandExtensions.Add(FileNameSuffixes.DotNet.DynamicLib);
+
+            return allowedCommandExtensions;
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/ProjectPathCommandResolver.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class ProjectPathCommandResolver : AbstractPathBasedCommandResolver
+    {
+        public ProjectPathCommandResolver(IEnvironmentProvider environment, 
+            IPlatformCommandSpecFactory commandSpecFactory) : base(environment, commandSpecFactory) { }
+
+        internal override string ResolveCommandPath(CommandResolverArguments commandResolverArguments)
+        {
+            if (commandResolverArguments.ProjectDirectory == null)
+            {
+                return null;
+            }
+
+            return _environment.GetCommandPathFromRootPath(
+                commandResolverArguments.ProjectDirectory, 
+                commandResolverArguments.CommandName,
+                commandResolverArguments.InferredExtensions.EmptyIfNull());
+        }
+
+        internal override CommandResolutionStrategy GetCommandResolutionStrategy()
+        {
+            return CommandResolutionStrategy.ProjectLocal;
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/ProjectToolsCommandResolver.cs

@@ -0,0 +1,141 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class ProjectToolsCommandResolver : ICommandResolver
+    {
+        private static readonly NuGetFramework s_toolPackageFramework = FrameworkConstants.CommonFrameworks.NetStandardApp15;
+        private static readonly CommandResolutionStrategy s_commandResolutionStrategy = 
+            CommandResolutionStrategy.ProjectToolsPackage;
+
+        private List<string> _allowedCommandExtensions;
+        private IPackagedCommandSpecFactory _packagedCommandSpecFactory;
+
+        public ProjectToolsCommandResolver(IPackagedCommandSpecFactory packagedCommandSpecFactory)
+        {
+            _packagedCommandSpecFactory = packagedCommandSpecFactory;
+
+            _allowedCommandExtensions = new List<string>() 
+            {
+                FileNameSuffixes.DotNet.DynamicLib
+            };
+        }
+
+        public CommandSpec Resolve(CommandResolverArguments commandResolverArguments)
+        {
+            return ResolveFromProjectTools(
+                commandResolverArguments.CommandName, 
+                commandResolverArguments.CommandArguments,
+                commandResolverArguments.ProjectDirectory);
+        }
+
+        private CommandSpec ResolveFromProjectTools(
+            string commandName, 
+            IEnumerable<string> args,
+            string projectDirectory)
+        {
+            var projectContext = GetProjectContextFromDirectory(projectDirectory, s_toolPackageFramework);
+
+            if (projectContext == null)
+            {
+                return null;
+            }
+
+            var toolsLibraries = projectContext.ProjectFile.Tools.EmptyIfNull();
+
+            return ResolveCommandSpecFromAllToolLibraries(
+                toolsLibraries,
+                commandName, 
+                args,
+                projectContext);
+        }
+
+        private CommandSpec ResolveCommandSpecFromAllToolLibraries(
+            IEnumerable<LibraryRange> toolsLibraries,
+            string commandName,
+            IEnumerable<string> args,
+            ProjectContext projectContext)
+        {
+            foreach (var toolLibrary in toolsLibraries)
+            {
+                var commandSpec = ResolveCommandSpecFromToolLibrary(toolLibrary, commandName, args, projectContext);
+
+                if (commandSpec != null)
+                {
+                    return commandSpec;
+                }
+            }
+
+            return null;
+        }
+
+        private CommandSpec ResolveCommandSpecFromToolLibrary(
+            LibraryRange toolLibrary,
+            string commandName,
+            IEnumerable<string> args,
+            ProjectContext projectContext)
+        {
+            //todo: change this for new resolution strategy
+            var lockFilePath = Path.Combine(
+                projectContext.ProjectDirectory, 
+                "artifacts", "Tools", toolLibrary.Name,
+                "project.lock.json"); 
+
+            if (!File.Exists(lockFilePath))
+            {
+                return null;
+            }
+
+            var lockFile = LockFileReader.Read(lockFilePath);
+
+            var lockFilePackageLibrary = lockFile.PackageLibraries.FirstOrDefault(l => l.Name == toolLibrary.Name);
+            
+            var nugetPackagesRoot = projectContext.PackagesDirectory;
+
+            return _packagedCommandSpecFactory.CreateCommandSpecFromLibrary(
+                    lockFilePackageLibrary,
+                    commandName,
+                    args,
+                    _allowedCommandExtensions,
+                    projectContext.PackagesDirectory,
+                    s_commandResolutionStrategy,
+                    null);
+        }
+
+        private ProjectContext GetProjectContextFromDirectory(string directory, NuGetFramework framework)
+        {
+            if (directory == null || framework == null)
+            {
+                return null;
+            }
+
+            var projectRootPath = directory;
+
+            if (!File.Exists(Path.Combine(projectRootPath, Project.FileName)))
+            {
+                return null;
+            }
+
+            var projectContext = ProjectContext.Create(
+                projectRootPath, 
+                framework, 
+                PlatformServices.Default.Runtime.GetAllCandidateRuntimeIdentifiers());
+
+            if (projectContext.RuntimeIdentifier == null)
+            {
+                return null;
+            }
+
+            return projectContext;
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/ProjectToolsPackageCommandResolver.cs

@@ -0,0 +1,141 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class ProjectToolsCommandResolver : ICommandResolver
+    {
+        private static readonly NuGetFramework s_toolPackageFramework = FrameworkConstants.CommonFrameworks.DnxCore50;
+        private static readonly CommandResolutionStrategy s_commandResolutionStrategy = 
+            CommandResolutionStrategy.ProjectToolsPackage;
+
+        private List<string> _allowedCommandExtensions;
+        private IPackagedCommandSpecFactory _packagedCommandSpecFactory;
+
+        public ProjectToolsCommandResolver(IPackagedCommandSpecFactory packagedCommandSpecFactory)
+        {
+            _packagedCommandSpecFactory = packagedCommandSpecFactory;
+
+            _allowedCommandExtensions = new List<string>() 
+            {
+                FileNameSuffixes.DotNet.DynamicLib
+            };
+        }
+
+        public CommandSpec Resolve(CommandResolverArguments commandResolverArguments)
+        {
+            return ResolveFromProjectTools(
+                commandResolverArguments.CommandName, 
+                commandResolverArguments.CommandArguments,
+                commandResolverArguments.ProjectDirectory);
+        }
+
+        private CommandSpec ResolveFromProjectTools(
+            string commandName, 
+            IEnumerable<string> args,
+            string projectDirectory)
+        {
+            var projectContext = GetProjectContextFromDirectory(projectDirectory, s_toolPackageFramework);
+
+            if (projectContext == null)
+            {
+                return null;
+            }
+
+            var toolsLibraries = projectContext.ProjectFile.Tools.EmptyIfNull();
+
+            return ResolveCommandSpecFromAllToolLibraries(
+                toolsLibraries,
+                commandName, 
+                args,
+                projectContext);
+        }
+
+        private CommandSpec ResolveCommandSpecFromAllToolLibraries(
+            IEnumerable<LibraryRange> toolsLibraries,
+            string commandName,
+            IEnumerable<string> args,
+            ProjectContext projectContext)
+        {
+            foreach (var toolLibrary in toolsLibraries)
+            {
+                var commandSpec = ResolveCommandSpecFromToolLibrary(toolLibrary, commandName, args, projectContext);
+
+                if (commandSpec != null)
+                {
+                    return commandSpec;
+                }
+            }
+
+            return null;
+        }
+
+        private CommandSpec ResolveCommandSpecFromToolLibrary(
+            LibraryRange toolLibrary,
+            string commandName,
+            IEnumerable<string> args,
+            ProjectContext projectContext)
+        {
+            //todo: change this for new resolution strategy
+            var lockFilePath = Path.Combine(
+                projectContext.ProjectDirectory, 
+                "artifacts", "Tools", toolLibrary.Name,
+                "project.lock.json"); 
+
+            if (!File.Exists(lockFilePath))
+            {
+                return null;
+            }
+
+            var lockFile = LockFileReader.Read(lockFilePath);
+
+            var lockFilePackageLibrary = lockFile.PackageLibraries.FirstOrDefault(l => l.Name == toolLibrary.Name);
+            
+            var nugetPackagesRoot = projectContext.PackagesDirectory;
+
+            return _packagedCommandSpecFactory.CreateCommandSpecFromLibrary(
+                    lockFilePackageLibrary,
+                    commandName,
+                    args,
+                    _allowedCommandExtensions,
+                    projectContext.PackagesDirectory,
+                    s_commandResolutionStrategy,
+                    null);
+        }
+
+        private ProjectContext GetProjectContextFromDirectory(string directory, NuGetFramework framework)
+        {
+            if (directory == null || framework == null)
+            {
+                return null;
+            }
+
+            var projectRootPath = directory;
+
+            if (!File.Exists(Path.Combine(projectRootPath, Project.FileName)))
+            {
+                return null;
+            }
+
+            var projectContext = ProjectContext.Create(
+                projectRootPath, 
+                framework, 
+                PlatformServices.Default.Runtime.GetAllCandidateRuntimeIdentifiers());
+
+            if (projectContext.RuntimeIdentifier == null)
+            {
+                return null;
+            }
+
+            return projectContext;
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/RootedCommandResolver.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class RootedCommandResolver : ICommandResolver
+    {
+        public CommandSpec Resolve(CommandResolverArguments commandResolverArguments)
+        {
+            if (commandResolverArguments.CommandName == null)
+            {
+                return null;
+            }
+
+            if (Path.IsPathRooted(commandResolverArguments.CommandName))
+            {
+                var escapedArgs = ArgumentEscaper.EscapeAndConcatenateArgArrayForProcessStart(
+                    commandResolverArguments.CommandArguments.EmptyIfNull());
+
+                return new CommandSpec(commandResolverArguments.CommandName, escapedArgs, CommandResolutionStrategy.RootedPath);
+            }
+
+            return null;
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/ScriptCommandResolver.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class ScriptCommandResolver : CompositeCommandResolver
+    {
+        public static ScriptCommandResolver Create()
+        {
+            var environment = new EnvironmentProvider();
+
+            var platformCommandSpecFactory = default(IPlatformCommandSpecFactory);
+            if (PlatformServices.Default.Runtime.OperatingSystemPlatform == Platform.Windows)
+            {
+                platformCommandSpecFactory = new WindowsExePreferredCommandSpecFactory();
+            }
+            else
+            {
+                platformCommandSpecFactory = new GenericPlatformCommandSpecFactory();
+            }
+
+            return new ScriptCommandResolver(environment, platformCommandSpecFactory);
+        }
+
+        public ScriptCommandResolver(
+            IEnvironmentProvider environment,
+            IPlatformCommandSpecFactory platformCommandSpecFactory)
+        {
+            AddCommandResolver(new RootedCommandResolver());
+            AddCommandResolver(new ProjectPathCommandResolver(environment, platformCommandSpecFactory));
+            AddCommandResolver(new AppBaseCommandResolver(environment, platformCommandSpecFactory));
+            AddCommandResolver(new PathCommandResolver(environment, platformCommandSpecFactory));
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolution/WindowsExePreferredCommandSpecFactory.cs

@@ -0,0 +1,79 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.ProjectModel.Graph;
+using Microsoft.Extensions.PlatformAbstractions;
+using NuGet.Frameworks;
+using NuGet.Packaging;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class WindowsExePreferredCommandSpecFactory : IPlatformCommandSpecFactory
+    {
+        public CommandSpec CreateCommandSpec(
+           string commandName,
+           IEnumerable<string> args,
+           string commandPath,
+           CommandResolutionStrategy resolutionStrategy,
+           IEnvironmentProvider environment)
+        {
+            var useCmdWrapper = false;
+
+            if (Path.GetExtension(commandPath).Equals(".cmd", StringComparison.OrdinalIgnoreCase))
+            {
+                var preferredCommandPath = environment.GetCommandPath(commandName, ".exe");
+
+                if (preferredCommandPath == null)
+                {
+                    useCmdWrapper = true;
+                }
+                else
+                {
+                    commandPath = preferredCommandPath;
+                }
+            }
+
+            return useCmdWrapper 
+                ? CreateCommandSpecWrappedWithCmd(commandPath, args, resolutionStrategy)
+                : CreateCommandSpecFromExecutable(commandPath, args, resolutionStrategy);
+        }
+
+        private CommandSpec CreateCommandSpecFromExecutable(
+            string command,
+            IEnumerable<string> args,
+            CommandResolutionStrategy resolutionStrategy)
+        {
+            var escapedArgs = ArgumentEscaper.EscapeAndConcatenateArgArrayForProcessStart(args);
+            return new CommandSpec(command, escapedArgs, resolutionStrategy);
+        }
+
+        private CommandSpec CreateCommandSpecWrappedWithCmd(
+            string command,
+            IEnumerable<string> args,
+            CommandResolutionStrategy resolutionStrategy)
+        {
+            var comSpec = Environment.GetEnvironmentVariable("ComSpec") ?? "cmd.exe";
+
+            // Handle the case where ComSpec is already the command
+            if (command.Equals(comSpec, StringComparison.OrdinalIgnoreCase))
+            {
+                command = args.FirstOrDefault();
+                args = args.Skip(1);
+            }
+
+            var cmdEscapedArgs = ArgumentEscaper.EscapeAndConcatenateArgArrayForCmdProcessStart(args);
+
+            if (ArgumentEscaper.ShouldSurroundWithQuotes(command))
+            {
+                command = $"\"{command}\"";
+            }
+
+            var escapedArgString = $"/s /c \"{command} {cmdEscapedArgs}\"";
+
+            return new CommandSpec(comSpec, escapedArgString, resolutionStrategy);
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/CommandResolutionStrategy.cs

@@ -1,20 +0,0 @@
-namespace Microsoft.DotNet.Cli.Utils
-{
-    public enum CommandResolutionStrategy
-    {
-        //command loaded from a nuget package
-        NugetPackage,
-
-        //command loaded from the same directory as the executing assembly
-        BaseDirectory,
-
-        //command loaded from the same directory as a project.json file
-        ProjectLocal,
-
-        //command loaded from path
-        Path,
-
-        //command not found
-        None
-    }
-}

src/Microsoft.DotNet.Cli.Utils/CommandResolver.cs

@@ -13,6 +13,7 @@ namespace Microsoft.DotNet.Cli.Utils
 {
     internal static class CommandResolver
     {
+<<<<<<< HEAD
         public static CommandSpec TryResolveCommandSpec(
             string commandName,
             IEnumerable<string> args,
@@ -130,148 +131,55 @@ namespace Microsoft.DotNet.Cli.Utils
 
             var commandLibrary = context.ProjectFile.Tools
                 .FirstOrDefault(l => l.Name == commandName);
+=======
+        private static DefaultCommandResolver _defaultCommandResolver;
+        private static ScriptCommandResolver _scriptCommandResolver;
+>>>>>>> 9c4329a... Refactor CommandResolver into individual CommandResolver Implementation
 
-            if (commandLibrary == default(LibraryRange))
-            {
-                return null;
-            }
-
-            var lockPath = Path.Combine(context.ProjectDirectory, "artifacts", "Tools", commandName,
-                "project.lock.json");
-
-            if (!File.Exists(lockPath))
-            {
-                return null;
-            }
-
-            var lockFile = LockFileReader.Read(lockPath);
-
-            var lib = lockFile.PackageLibraries.FirstOrDefault(l => l.Name == commandName);
-            var packageDir = new VersionFolderPathResolver(context.PackagesDirectory)
-                .GetInstallPath(lib.Name, lib.Version);
-
-            return Directory.Exists(packageDir)
-                ? ConfigureCommandFromPackage(commandName, args, lib.Files, packageDir)
-                : null;
-        }
-
-        private static CommandSpec ConfigureCommandFromPackage(string commandName, IEnumerable<string> args, string packageDir)
+        public static CommandSpec TryResolveCommandSpec(
+            string commandName, 
+            IEnumerable<string> args, 
+            NuGetFramework framework = null, 
+            string configuration=Constants.DefaultConfiguration, 
+            string outputPath=null)
         {
-            var commandPackage = new PackageFolderReader(packageDir);
+            var commandResolverArgs = new CommandResolverArguments
+            {
+                CommandName = commandName,
+                CommandArguments = args,
+                Framework = framework,
+                ProjectDirectory = Directory.GetCurrentDirectory(),
+                Configuration = configuration
+            };
 
-            var files = commandPackage.GetFiles();
+            if (_defaultCommandResolver == null)
+            {
+                _defaultCommandResolver = DefaultCommandResolver.Create();
+            }
 
-            return ConfigureCommandFromPackage(commandName, args, files, packageDir);
+            return _defaultCommandResolver.Resolve(commandResolverArgs);
         }
-
-        private static CommandSpec ConfigureCommandFromPackage(string commandName, IEnumerable<string> args,
-            PackageDescription commandPackage, ProjectContext projectContext, string depsPath = null)
+        
+        public static CommandSpec TryResolveScriptCommandSpec(
+            string commandName, 
+            IEnumerable<string> args, 
+            Project project, 
+            string[] inferredExtensionList)
         {
-            var files = commandPackage.Library.Files;
-
-            var packageRoot = projectContext.PackagesDirectory;
-
-            var packagePath = commandPackage.Path;
-
-            var packageDir = Path.Combine(packageRoot, packagePath);
-
-            return ConfigureCommandFromPackage(commandName, args, files, packageDir, depsPath);
-        }
-
-        private static CommandSpec ConfigureCommandFromPackage(string commandName, IEnumerable<string> args,
-            IEnumerable<string> files, string packageDir, string depsPath = null)
-        {
-            var fileName = string.Empty;
-
-            var commandPath = files
-                .FirstOrDefault(f => Env.ExecutableExtensions.Contains(Path.GetExtension(f)));
-
-            if (commandPath == null)
+            var commandResolverArgs = new CommandResolverArguments
             {
-                var dllPath = files
-                    .Where(f => Path.GetFileName(f) == commandName + FileNameSuffixes.DotNet.DynamicLib)
-                    .Select(f => Path.Combine(packageDir, f))
-                    .FirstOrDefault();
+                CommandName = commandName,
+                CommandArguments = args,
+                ProjectDirectory = project.ProjectDirectory,
+                InferredExtensions = inferredExtensionList
+            };
 
-                fileName = CoreHost.HostExePath;
-
-                var additionalArgs = new List<string>();
-                additionalArgs.Add(dllPath);
-
-                if (depsPath != null)
-                {
-                    additionalArgs.Add($"--depsfile:{depsPath}");
-                }
-
-                args = additionalArgs.Concat(args);
-            }
-            else
+            if (_scriptCommandResolver == null)
             {
-                fileName = Path.Combine(packageDir, commandPath);
+                _scriptCommandResolver = ScriptCommandResolver.Create();
             }
 
-            var escapedArgs = ArgumentEscaper.EscapeAndConcatenateArgArrayForProcessStart(args);
-            return new CommandSpec(fileName, escapedArgs, CommandResolutionStrategy.NugetPackage);
-        }
-
-        private static CommandSpec CreateCommandSpecPreferringExe(
-            string commandName,
-            IEnumerable<string> args,
-            string commandPath,
-            CommandResolutionStrategy resolutionStrategy)
-        {
-            var useComSpec = false;
-            
-            if (PlatformServices.Default.Runtime.OperatingSystemPlatform == Platform.Windows &&
-                Path.GetExtension(commandPath).Equals(".cmd", StringComparison.OrdinalIgnoreCase))
-            {
-                var preferredCommandPath = Env.GetCommandPath(commandName, ".exe");
-
-                // Use cmd if we can't find an exe
-                if (preferredCommandPath == null)
-                {
-                    useComSpec = true;
-                }
-                else
-                {
-                    commandPath = preferredCommandPath;
-                }
-            }
-
-            if (useComSpec)
-            {
-                return CreateCmdCommandSpec(commandPath, args, resolutionStrategy);
-            }
-            else
-            {
-                var escapedArgs = ArgumentEscaper.EscapeAndConcatenateArgArrayForProcessStart(args);
-                return new CommandSpec(commandPath, escapedArgs, resolutionStrategy);
-            }
-        }
-
-        private static CommandSpec CreateCmdCommandSpec(
-            string command,
-            IEnumerable<string> args,
-            CommandResolutionStrategy resolutionStrategy)
-        {
-            var comSpec = Environment.GetEnvironmentVariable("ComSpec");
-            
-            // Handle the case where ComSpec is already the command
-            if (command.Equals(comSpec, StringComparison.OrdinalIgnoreCase))
-            {
-                command = args.FirstOrDefault();
-                args = args.Skip(1);
-            }
-            var cmdEscapedArgs = ArgumentEscaper.EscapeAndConcatenateArgArrayForCmdProcessStart(args);
-
-            if (ArgumentEscaper.ShouldSurroundWithQuotes(command))
-            {
-                command = $"\"{command}\"";
-            }
-
-            var escapedArgString = $"/s /c \"{command} {cmdEscapedArgs}\"";
-
-            return new CommandSpec(comSpec, escapedArgString, resolutionStrategy);
+            return _scriptCommandResolver.Resolve(commandResolverArgs);
         }
     }
 }

src/Microsoft.DotNet.Cli.Utils/CommandSpec.cs

@@ -1,6 +1,6 @@
 namespace Microsoft.DotNet.Cli.Utils
 {
-    internal class CommandSpec
+    public class CommandSpec
     {
         public CommandSpec(string path, string args, CommandResolutionStrategy resolutionStrategy)
         {

src/Microsoft.DotNet.Cli.Utils/Env.cs

@@ -9,74 +9,29 @@ namespace Microsoft.DotNet.Cli.Utils
 {
     public static class Env
     {
-        private static IEnumerable<string> _searchPaths;
-        private static IEnumerable<string> _executableExtensions;
+        private static IEnvironmentProvider _environment = new EnvironmentProvider();
 
         public static IEnumerable<string> ExecutableExtensions
         {
             get
             {
-                if (_executableExtensions == null)
-                {
-
-                    _executableExtensions = PlatformServices.Default.Runtime.OperatingSystemPlatform == Platform.Windows
-                        ? Environment.GetEnvironmentVariable("PATHEXT")
-                            .Split(';')
-                            .Select(e => e.ToLower().Trim('"'))
-                        : new [] { string.Empty };
-                }
-
-                return _executableExtensions;
-            }
-        } 
-
-        private static IEnumerable<string> SearchPaths 
-        {
-            get
-            {
-                if (_searchPaths == null)
-                {
-                    var searchPaths = new List<string> { PlatformServices.Default.Application.ApplicationBasePath };
-
-                    searchPaths.AddRange(Environment
-                        .GetEnvironmentVariable("PATH")
-                        .Split(Path.PathSeparator)
-                        .Select(p => p.Trim('"')));
-
-                    _searchPaths = searchPaths;
-                }
-
-                return _searchPaths;
+                return _environment.ExecutableExtensions;
             }
         }
 
         public static string GetCommandPath(string commandName, params string[] extensions)
         {
-            if (!extensions.Any())
-            {
-                extensions = Env.ExecutableExtensions.ToArray();
-            }
-
-            var commandPath = Env.SearchPaths.Join(
-                extensions,
-                    p => true, s => true,
-                    (p, s) => Path.Combine(p, commandName + s))
-                .FirstOrDefault(File.Exists);
-
-            return commandPath;
+            return _environment.GetCommandPath(commandName, extensions);
         }
 
         public static string GetCommandPathFromRootPath(string rootPath, string commandName, params string[] extensions)
         {
-            if (!extensions.Any())
-            {
-                extensions = Env.ExecutableExtensions.ToArray();
-            }
+            return _environment.GetCommandPathFromRootPath(rootPath, commandName, extensions);
+        }
 
-            var commandPath = extensions.Select(e => Path.Combine(rootPath, commandName + e))
-                .FirstOrDefault(File.Exists);
-
-            return commandPath;
+        public static string GetCommandPathFromRootPath(string rootPath, string commandName, IEnumerable<string> extensions)
+        {
+            return _environment.GetCommandPathFromRootPath(rootPath, commandName, extensions);
         }
     }
 }

src/Microsoft.DotNet.Cli.Utils/EnvironmentProvider.cs

@@ -0,0 +1,97 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.Extensions.PlatformAbstractions;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public class EnvironmentProvider : IEnvironmentProvider
+    {
+        private IEnumerable<string> _searchPaths;
+        private IEnumerable<string> _executableExtensions;
+
+        public IEnumerable<string> ExecutableExtensions
+        {
+            get
+            {
+                if (_executableExtensions == null)
+                {
+
+                    _executableExtensions = PlatformServices.Default.Runtime.OperatingSystemPlatform == Platform.Windows
+                        ? Environment.GetEnvironmentVariable("PATHEXT")
+                            .Split(';')
+                            .Select(e => e.ToLower().Trim('"'))
+                        : new [] { string.Empty };
+                }
+
+                return _executableExtensions;
+            }
+        } 
+
+        private IEnumerable<string> SearchPaths 
+        {
+            get
+            {
+                if (_searchPaths == null)
+                {
+                    var searchPaths = new List<string> { PlatformServices.Default.Application.ApplicationBasePath };
+
+                    searchPaths.AddRange(Environment
+                        .GetEnvironmentVariable("PATH")
+                        .Split(Path.PathSeparator)
+                        .Select(p => p.Trim('"')));
+
+                    _searchPaths = searchPaths;
+                }
+
+                return _searchPaths;
+            }
+        }
+
+        public EnvironmentProvider(IEnumerable<string> extensionsOverride = null)
+        {
+            if (extensionsOverride != null)
+            {
+                _executableExtensions = extensionsOverride;
+            }
+        }
+
+        public string GetCommandPath(string commandName, params string[] extensions)
+        {
+            if (!extensions.Any())
+            {
+                extensions = ExecutableExtensions.ToArray();
+            }
+
+            var commandPath = SearchPaths.Join(
+                extensions,
+                    p => true, s => true,
+                    (p, s) => Path.Combine(p, commandName + s))
+                .FirstOrDefault(File.Exists);
+
+            return commandPath;
+        }
+
+        public string GetCommandPathFromRootPath(string rootPath, string commandName, params string[] extensions)
+        {
+            if (!extensions.Any())
+            {
+                extensions = ExecutableExtensions.ToArray();
+            }
+
+            var commandPath = extensions.Select(e => Path.Combine(rootPath, commandName + e))
+                .FirstOrDefault(File.Exists);
+
+            return commandPath;
+        }
+
+        public string GetCommandPathFromRootPath(string rootPath, string commandName, IEnumerable<string> extensions)
+        {
+            var extensionsArr = extensions.EmptyIfNull().ToArray();
+
+            return GetCommandPathFromRootPath(rootPath, commandName, extensionsArr);
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/Extensions/CollectionsExtensions.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public static class CollectionsExtensions
+    {
+        public static IEnumerable<T> EmptyIfNull<T>(this IEnumerable<T> enumerable)
+        {
+            return enumerable == null 
+                ? Enumerable.Empty<T>()
+                : enumerable;
+        }
+    }
+}

src/Microsoft.DotNet.Cli.Utils/IEnvironmentProvider.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Microsoft.Extensions.PlatformAbstractions;
+
+namespace Microsoft.DotNet.Cli.Utils
+{
+    public interface IEnvironmentProvider
+    {
+        IEnumerable<string> ExecutableExtensions { get; }
+
+        string GetCommandPath(string commandName, params string[] extensions);
+
+        string GetCommandPathFromRootPath(string rootPath, string commandName, params string[] extensions);
+
+        string GetCommandPathFromRootPath(string rootPath, string commandName, IEnumerable<string> extensions);
+    }
+}

test/Microsoft.DotNet.Cli.Utils.Tests/CommandResolverTestUtils.cs

@@ -0,0 +1,25 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.IO;
+
+namespace Microsoft.DotNet.Cli.Utils.Tests
+{
+    public static class CommandResolverTestUtils
+    {
+        public static void CreateNonRunnableTestCommand(string directory, string filename, string extension=".dll")
+        {
+            Directory.CreateDirectory(directory);
+            
+            var filePath = Path.Combine(directory, filename + extension);
+
+            File.WriteAllText(filePath, "test command that does nothing.");
+        }
+
+        public static IEnvironmentProvider SetupEnvironmentProviderWhichFindsExtensions(params string[] extensions)
+        {
+            return new EnvironmentProvider(extensions);
+        }
+    }
+}

test/Microsoft.DotNet.Cli.Utils.Tests/GivenACompositeCommandResolver.cs

@@ -0,0 +1,86 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Linq;
+using Xunit;
+using Moq;
+using Microsoft.DotNet.Cli.Utils;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.Tools.Test.Utilities;
+using Microsoft.Extensions.PlatformAbstractions;
+using System.Threading;
+using FluentAssertions;
+using NuGet.Frameworks;
+
+namespace Microsoft.DotNet.Cli.Utils.Tests
+{
+    public class GivenACompositeCommandResolver
+    {
+        [Fact]
+        public void It_iterates_through_all_added_resolvers_in_order_when_they_return_null()
+        {
+            var compositeCommandResolver = new CompositeCommandResolver();
+
+            var resolverCalls = new List<int>();
+
+            var mockResolver1 = new Mock<ICommandResolver>();
+            mockResolver1.Setup(r => r
+                .Resolve(It.IsAny<CommandResolverArguments>()))
+                .Returns(default(CommandSpec))
+                .Callback(() => resolverCalls.Add(1));
+
+            var mockResolver2 = new Mock<ICommandResolver>();
+            mockResolver2.Setup(r => r
+                .Resolve(It.IsAny<CommandResolverArguments>()))
+                .Returns(default(CommandSpec))
+                .Callback(() => resolverCalls.Add(2));
+
+            compositeCommandResolver.AddCommandResolver(mockResolver1.Object);
+            compositeCommandResolver.AddCommandResolver(mockResolver2.Object);
+
+            compositeCommandResolver.Resolve(default(CommandResolverArguments));
+
+            resolverCalls.Should()
+                .HaveCount(2)
+                .And
+                .ContainInOrder(new [] {1, 2});
+
+        }
+
+        [Fact]
+        public void It_stops_iterating_through_added_resolvers_when_one_returns_nonnull()
+        {
+            var compositeCommandResolver = new CompositeCommandResolver();
+
+            var resolverCalls = new List<int>();
+
+            var mockResolver1 = new Mock<ICommandResolver>();
+            mockResolver1.Setup(r => r
+                .Resolve(It.IsAny<CommandResolverArguments>()))
+                .Returns(new CommandSpec(null, null, default(CommandResolutionStrategy)))
+                .Callback(() => resolverCalls.Add(1));
+
+            var mockResolver2 = new Mock<ICommandResolver>();
+            mockResolver2.Setup(r => r
+                .Resolve(It.IsAny<CommandResolverArguments>()))
+                .Returns(default(CommandSpec))
+                .Callback(() => resolverCalls.Add(2));
+
+            compositeCommandResolver.AddCommandResolver(mockResolver1.Object);
+            compositeCommandResolver.AddCommandResolver(mockResolver2.Object);
+
+            compositeCommandResolver.Resolve(default(CommandResolverArguments));
+
+            resolverCalls.Should()
+                .HaveCount(1)
+                .And
+                .ContainInOrder(new [] {1});
+
+        }
+    }
+}

test/Microsoft.DotNet.Cli.Utils.Tests/GivenADefaultCommandResolver.cs

@@ -0,0 +1,206 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Linq;
+using Xunit;
+using Moq;
+using Microsoft.DotNet.Cli.Utils;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.Tools.Test.Utilities;
+using Microsoft.Extensions.PlatformAbstractions;
+using System.Threading;
+using FluentAssertions;
+using NuGet.Frameworks;
+
+namespace Microsoft.DotNet.Cli.Utils.Tests
+{
+    public class GivenADefaultCommandResolver
+    {
+        [Fact]
+        public void It_contains_resolvers_in_the_right_order()
+        {
+            var defaultCommandResolver = DefaultCommandResolver.Create();
+
+            var resolvers = defaultCommandResolver.OrderedCommandResolvers;
+
+            resolvers.Should().HaveCount(5);
+
+            resolvers.Select(r => r.GetType())
+                .Should()
+                .ContainInOrder(
+                    new []{
+                        typeof(RootedCommandResolver),
+                        typeof(ProjectDependenciesCommandResolver),
+                        typeof(ProjectToolsCommandResolver),
+                        typeof(AppBaseCommandResolver),
+                        typeof(PathCommandResolver)
+                    });
+        }
+
+
+        // [Fact]
+        // public void It_Resolves_Rooted_Commands_Correctly()
+        // {
+        //     var path = Path.Combine(AppContext.BaseDirectory, "rooteddir");
+        //     Directory.CreateDirectory(path);
+
+        //     var testCommandPath = CreateTestCommandFile(path, ".dll", "rootedcommand");
+
+        //     var defaultCommandResolver = new DefaultCommandResolver();
+
+        //     var commandResolverArgs = new CommandResolverArguments
+        //     {
+        //         CommandName = testCommandPath,
+        //         CommandArguments = new string[] {}
+        //     };
+
+        //     var commandSpec = defaultCommandResolver.Resolve(commandResolverArgs);
+        //     commandSpec.Should().NotBeNull();
+
+        //     commandSpec.Path.Should().Be(testCommandPath);
+        //     commandSpec.ResolutionStrategy.Should().Be(CommandResolutionStrategy.RootedPath);
+        // }
+
+        // [Fact]
+        // public void It_Resolves_AppBase_Commands_Correctly()
+        // {
+        //     var testCommandPath = CreateTestCommandFile(AppContext.BaseDirectory, ".exe", "appbasecommand");
+        //     var testCommandName = Path.GetFileNameWithoutExtension(testCommandPath);
+
+        //     var defaultCommandResolver = new DefaultCommandResolver();
+
+        //     var commandResolverArgs = new CommandResolverArguments
+        //     {
+        //         CommandName = testCommandName,
+        //         CommandArguments = new string[] {}, 
+        //         Environment = new EnvironmentProvider()
+        //     };
+
+        //     var commandSpec = defaultCommandResolver.Resolve(commandResolverArgs);
+        //     commandSpec.Should().NotBeNull();
+
+        //     commandSpec.Path.Should().Be(testCommandPath);
+        //     commandSpec.ResolutionStrategy.Should().Be(CommandResolutionStrategy.BaseDirectory);
+        // }
+
+        // [Fact]
+        // public void It_Resolves_PATH_Commands_Correctly()
+        // {
+        //     var path = Path.Combine(AppContext.BaseDirectory, "pathdir");
+        //     var testCommandPath = CreateTestCommandFile(path, ".dll", "pathcommmand");
+        //     var testCommandName = Path.GetFileNameWithoutExtension(testCommandPath);
+
+        //     Mock<IEnvironmentProvider> mockEnvironment = new Mock<IEnvironmentProvider>();
+        //     mockEnvironment.Setup(c => c
+        //         .GetCommandPath(It.IsAny<string>(), It.IsAny<string[]>()))
+        //         .Returns(testCommandPath);
+
+        //     var defaultCommandResolver = new DefaultCommandResolver();
+
+        //     var commandResolverArgs = new CommandResolverArguments
+        //     {
+        //         CommandName = testCommandName,
+        //         CommandArguments = new string[] {}, 
+        //         Environment = mockEnvironment.Object
+        //     };
+
+        //     var commandSpec = defaultCommandResolver.Resolve(commandResolverArgs);
+        //     commandSpec.Should().NotBeNull();
+
+        //     commandSpec.Path.Should().Be(testCommandPath);
+        //     commandSpec.ResolutionStrategy.Should().Be(CommandResolutionStrategy.Path);
+        // }
+
+        // [Fact]
+        // public void It_Resolves_Project_Tools_Commands_Correctly()
+        // {
+        //     var testAppPath = Path.Combine(AppContext.BaseDirectory, 
+        //         "TestAssets/TestProjects/AppWithToolDependency");
+
+        //     var defaultCommandResolver = new DefaultCommandResolver();
+
+        //     var commandResolverArgs = new CommandResolverArguments
+        //     {
+        //         CommandName = "dotnet-hello",
+        //         CommandArguments = new string[] {}, 
+        //         ProjectDirectory = testAppPath,
+        //         Environment = new EnvironmentProvider()
+        //     };
+
+        //     var commandSpec = defaultCommandResolver.Resolve(commandResolverArgs);
+        //     commandSpec.Should().NotBeNull();
+
+        //     commandSpec.Path.Should().NotBeNull();
+        //     commandSpec.Args.Should().NotContain("--depsfile");
+        //     commandSpec.ResolutionStrategy.Should().Be(CommandResolutionStrategy.NugetPackage);
+        // }
+
+        // [Fact]
+        // public void It_Resolves_Project_Dependencies_Commands_Correctly()
+        // {
+        //     var testAppPath = Path.Combine(AppContext.BaseDirectory, 
+        //         "TestAssets/TestProjects/AppWithDirectDependency");
+
+        //     var defaultCommandResolver = new DefaultCommandResolver();
+
+        //     var commandResolverArgs = new CommandResolverArguments
+        //     {
+        //         CommandName = "dotnet-hello",
+        //         CommandArguments = new string[] {}, 
+        //         ProjectDirectory = testAppPath,
+        //         Environment = new EnvironmentProvider(),
+        //         Framework = FrameworkConstants.CommonFrameworks.DnxCore50,
+        //         Configuration = "Debug"
+        //     };
+
+
+        //     var commandSpec = defaultCommandResolver.Resolve(commandResolverArgs);
+        //     commandSpec.Should().NotBeNull();
+
+        //     commandSpec.Path.Should().NotBeNull();
+        //     commandSpec.Args.Should().Contain("--depsfile");
+        //     commandSpec.ResolutionStrategy.Should().Be(CommandResolutionStrategy.NugetPackage);
+        // }
+
+        // [Fact]
+        // public void It_does_not_resolve_ProjectLocal_commands()
+        // {
+        //     var path = Path.Combine(AppContext.BaseDirectory, 
+        //         "testdir");
+
+        //     var testCommandPath = CreateTestCommandFile(path, ".exe", "projectlocalcommand");
+        //     var testCommandName = Path.GetFileNameWithoutExtension(testCommandPath);
+
+        //     var defaultCommandResolver = new DefaultCommandResolver();
+
+        //     var commandResolverArgs = new CommandResolverArguments
+        //     {
+        //         CommandName = testCommandName,
+        //         CommandArguments = new string[] {}, 
+        //         ProjectDirectory = path,
+        //         Environment = new EnvironmentProvider()
+        //     };
+
+        //     var commandSpec = defaultCommandResolver.Resolve(commandResolverArgs);
+
+        //     commandSpec.Should().Be(null);
+        // }
+
+        // public string CreateTestCommandFile(string path, string extension, string name = "testcommand")
+        // {
+        //     Directory.CreateDirectory(path);
+
+        //     var filename = name + extension;
+        //     var filepath = Path.Combine(path, filename);
+
+        //     File.WriteAllText(filepath, "hello world");
+
+        //     return filepath;
+        // }
+    }
+}

test/Microsoft.DotNet.Cli.Utils.Tests/GivenAProjectPathCommandResolver.cs

@@ -0,0 +1,239 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Linq;
+using Xunit;
+using Moq;
+using Microsoft.DotNet.Cli.Utils;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.Tools.Test.Utilities;
+using Microsoft.Extensions.PlatformAbstractions;
+using System.Threading;
+using FluentAssertions;
+using NuGet.Frameworks;
+
+namespace Microsoft.DotNet.Cli.Utils.Tests
+{
+    public class GivenAProjectPathCommandResolver
+    {
+        private static readonly string s_testProjectDirectory = Path.Combine(AppContext.BaseDirectory, "testprojectdirectory");
+
+        [Fact]
+        public void It_returns_null_when_CommandName_is_null()
+        {
+            var projectPathCommandResolver = SetupPlatformProjectPathCommandResolver();
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = null,
+                CommandArguments = new string[] {""},
+                ProjectDirectory = "/some/directory"
+            };
+
+            var result = projectPathCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().BeNull();
+        }
+
+        [Fact]
+        public void It_returns_null_when_ProjectDirectory_is_null()
+        {
+            var projectPathCommandResolver = SetupPlatformProjectPathCommandResolver();
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "command",
+                CommandArguments = new string[] {""},
+                ProjectDirectory = null
+            };
+
+            var result = projectPathCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().BeNull();
+        }
+
+        [Fact]
+        public void It_returns_null_when_CommandName_does_not_exist_in_ProjectDirectory()
+        {
+            var projectPathCommandResolver = SetupPlatformProjectPathCommandResolver();
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "nonexistent-command",
+                CommandArguments = null,
+                ProjectDirectory = s_testProjectDirectory
+            };
+
+            var result = projectPathCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().BeNull();
+        }
+
+        [Fact]
+        public void It_returns_null_when_CommandName_exists_in_a_subdirectory_of_ProjectDirectory()
+        {
+            var environment = CommandResolverTestUtils.SetupEnvironmentProviderWhichFindsExtensions(".exe");
+            var projectPathCommandResolver = SetupPlatformProjectPathCommandResolver(environment);
+
+            var testDir = Path.Combine(s_testProjectDirectory, "projectpathtestsubdir");
+            CommandResolverTestUtils.CreateNonRunnableTestCommand(testDir, "projectpathtestsubdircommand", ".exe");
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "projectpathtestsubdircommand",
+                CommandArguments = null,
+                ProjectDirectory = s_testProjectDirectory
+            };
+
+            var result = projectPathCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().BeNull();
+        }
+
+        [Fact]
+        public void It_returns_a_CommandSpec_with_CommandName_as_FileName_when_CommandName_exists_in_ProjectDirectory()
+        {
+            var environment = CommandResolverTestUtils.SetupEnvironmentProviderWhichFindsExtensions(".exe");
+            var projectPathCommandResolver = SetupPlatformProjectPathCommandResolver(environment);
+
+            CommandResolverTestUtils.CreateNonRunnableTestCommand(s_testProjectDirectory, "projectpathtestcommand1", ".exe");
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "projectpathtestcommand1",
+                CommandArguments = null,
+                ProjectDirectory = s_testProjectDirectory
+            };
+
+            var result = projectPathCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().NotBeNull();
+
+            var commandFile = Path.GetFileNameWithoutExtension(result.Path);
+
+            commandFile.Should().Be("projectpathtestcommand1");
+        }
+
+        [Fact]
+        public void It_escapes_CommandArguments_when_returning_a_CommandSpec()
+        {
+            var environment = CommandResolverTestUtils.SetupEnvironmentProviderWhichFindsExtensions(".exe");
+            var projectPathCommandResolver = SetupPlatformProjectPathCommandResolver(environment);
+
+            CommandResolverTestUtils.CreateNonRunnableTestCommand(s_testProjectDirectory, "projectpathtestcommand1", ".exe");
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "projectpathtestcommand1",
+                CommandArguments = new [] { "arg with space"},
+                ProjectDirectory = s_testProjectDirectory
+            };
+
+            var result = projectPathCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().NotBeNull();
+            result.Args.Should().Be("\"arg with space\"");
+        }
+
+        [Fact]
+        public void It_resolves_commands_with_extensions_defined_in_InferredExtensions()
+        {
+            var extensions = new string[] {".sh", ".cmd", ".foo", ".exe"};
+            var projectPathCommandResolver = SetupPlatformProjectPathCommandResolver();
+
+            foreach (var extension in extensions)
+            {
+                var extensionTestDir = Path.Combine(s_testProjectDirectory, "testext" + extension);
+
+                CommandResolverTestUtils.CreateNonRunnableTestCommand(extensionTestDir, "projectpathexttest", extension);
+
+                var commandResolverArguments = new CommandResolverArguments()
+                {
+                    CommandName = "projectpathexttest",
+                    CommandArguments = null,
+                    ProjectDirectory = extensionTestDir,
+                    InferredExtensions = extensions
+                };
+
+                var result = projectPathCommandResolver.Resolve(commandResolverArguments);
+
+                result.Should().NotBeNull();
+
+                var commandFileName = Path.GetFileName(result.Path);
+                commandFileName.Should().Be("projectpathexttest" + extension);
+            }            
+        }
+
+        [Fact]
+        public void It_returns_a_CommandSpec_with_Args_as_stringEmpty_when_returning_a_CommandSpec_and_CommandArguments_are_null()
+        {
+            var environment = CommandResolverTestUtils.SetupEnvironmentProviderWhichFindsExtensions(".exe");
+            var projectPathCommandResolver = SetupPlatformProjectPathCommandResolver(environment);
+
+            CommandResolverTestUtils.CreateNonRunnableTestCommand(s_testProjectDirectory, "projectpathtestcommand1", ".exe");
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "projectpathtestcommand1",
+                CommandArguments = null,
+                ProjectDirectory = s_testProjectDirectory
+            };
+
+            var result = projectPathCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().NotBeNull();
+            result.Args.Should().Be(string.Empty);
+        }
+
+        [Fact]
+        public void It_prefers_EXE_over_CMD_when_two_command_candidates_exist_and_using_WindowsExePreferredCommandSpecFactory()
+        {
+            var environment = CommandResolverTestUtils.SetupEnvironmentProviderWhichFindsExtensions(".exe");
+            var platformCommandSpecFactory = new WindowsExePreferredCommandSpecFactory();
+
+            var projectPathCommandResolver = new ProjectPathCommandResolver(environment, platformCommandSpecFactory);
+
+            CommandResolverTestUtils.CreateNonRunnableTestCommand(s_testProjectDirectory, "projectpathtestcommand1", ".exe");
+            CommandResolverTestUtils.CreateNonRunnableTestCommand(s_testProjectDirectory, "projectpathtestcommand1", ".cmd");
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "projectpathtestcommand1",
+                CommandArguments = null,
+                ProjectDirectory = s_testProjectDirectory
+            };
+
+            var result = projectPathCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().NotBeNull();
+
+            var commandFile = Path.GetFileName(result.Path);
+            commandFile.Should().Be("projectpathtestcommand1.exe");
+        }
+
+        private ProjectPathCommandResolver SetupPlatformProjectPathCommandResolver(IEnvironmentProvider environment = null)
+        {
+            environment = environment ?? new EnvironmentProvider();
+
+            var platformCommandSpecFactory = default(IPlatformCommandSpecFactory);
+
+            if (PlatformServices.Default.Runtime.OperatingSystemPlatform == Platform.Windows)
+            {
+                platformCommandSpecFactory = new WindowsExePreferredCommandSpecFactory();
+            }
+            else
+            {
+                platformCommandSpecFactory = new GenericPlatformCommandSpecFactory();
+            }
+
+            var projectPathCommandResolver = new ProjectPathCommandResolver(environment, platformCommandSpecFactory);
+
+            return projectPathCommandResolver;
+        }
+    }
+}

test/Microsoft.DotNet.Cli.Utils.Tests/GivenARootedCommandResolver.cs

@@ -0,0 +1,111 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Linq;
+using Xunit;
+using Moq;
+using Microsoft.DotNet.Cli.Utils;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.Tools.Test.Utilities;
+using Microsoft.Extensions.PlatformAbstractions;
+using System.Threading;
+using FluentAssertions;
+using NuGet.Frameworks;
+
+namespace Microsoft.DotNet.Cli.Utils.Tests
+{
+    public class GivenARootedCommandResolver
+    {
+        [Fact]
+        public void It_returns_null_when_CommandName_is_null()
+        {
+            var rootedCommandResolver = new RootedCommandResolver();
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = null,
+                CommandArguments = null
+            };
+
+            var result = rootedCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().BeNull();
+        }
+
+        [Fact]
+        public void It_returns_null_when_CommandName_is_not_rooted()
+        {
+            var rootedCommandResolver = new RootedCommandResolver();
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "some/relative/path",
+                CommandArguments = null
+            };
+
+            var result = rootedCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().BeNull();
+        }
+
+        [Fact]
+        public void It_returns_a_CommandSpec_with_CommandName_as_Path_when_CommandName_is_rooted()
+        {
+            var rootedCommandResolver = new RootedCommandResolver();
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "/some/rooted/path",
+                CommandArguments = null
+            };
+
+            var result = rootedCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().NotBeNull();
+            result.Path.Should().Be(commandResolverArguments.CommandName);
+        }
+
+        [Fact]
+        public void It_escapes_CommandArguments_when_returning_a_CommandSpec()
+        {
+            var rootedCommandResolver = new RootedCommandResolver();
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "/some/rooted/path",
+                CommandArguments = new [] { "arg with space"}
+            };
+
+            var result = rootedCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().NotBeNull();
+            result.Path.Should().Be(commandResolverArguments.CommandName);
+
+            result.Args.Should().Be("\"arg with space\"");
+        }
+
+        [Fact]
+        public void It_returns_a_CommandSpec_with_Args_as_stringEmpty_when_returning_a_CommandSpec_and_CommandArguments_are_null()
+        {
+            var rootedCommandResolver = new RootedCommandResolver();
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "/some/rooted/path",
+                CommandArguments = null
+            };
+
+            var result = rootedCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().NotBeNull();
+            result.Path.Should().Be(commandResolverArguments.CommandName);
+
+            result.Args.Should().Be(string.Empty);
+        }
+    }
+}

test/Microsoft.DotNet.Cli.Utils.Tests/GivenAScriptCommandResolver.cs

@@ -0,0 +1,199 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+using Xunit;
+using Moq;
+using Microsoft.DotNet.Cli.Utils;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.Tools.Test.Utilities;
+using Microsoft.Extensions.PlatformAbstractions;
+using System.Threading;
+using FluentAssertions;
+using NuGet.Frameworks;
+
+namespace Microsoft.DotNet.Cli.Utils.Tests
+{
+    public class GivenAScriptCommandResolver
+    {
+        [Fact]
+        public void It_contains_resolvers_in_the_right_order()
+        {
+            var scriptCommandResolver = ScriptCommandResolver.Create();
+
+            var resolvers = scriptCommandResolver.OrderedCommandResolvers;
+
+            resolvers.Should().HaveCount(4);
+
+            resolvers.Select(r => r.GetType())
+                .Should()
+                .ContainInOrder(
+                    new []{
+                        typeof(RootedCommandResolver),
+                        typeof(ProjectPathCommandResolver),
+                        typeof(AppBaseCommandResolver),
+                        typeof(PathCommandResolver)
+                    });
+        }
+
+        // [Fact]
+        // public void It_Resolves_Rooted_Commands_Correctly()
+        // {
+        //     var path = Path.Combine(AppContext.BaseDirectory, "rooteddir");
+        //     Directory.CreateDirectory(path);
+
+        //     var testCommandPath = CreateTestCommandFile(path, ".dll", "scriptrootedcommand");
+
+        //     var scriptCommandResolver = new ScriptCommandResolver();
+
+        //     var commandResolverArgs = new CommandResolverArguments
+        //     {
+        //         CommandName = testCommandPath,
+        //         CommandArguments = new string[] {}
+        //     };
+
+        //     var commandSpec = scriptCommandResolver.Resolve(commandResolverArgs);
+        //     commandSpec.Should().NotBeNull();
+
+        //     commandSpec.Path.Should().Be(testCommandPath);
+        //     commandSpec.ResolutionStrategy.Should().Be(CommandResolutionStrategy.RootedPath);
+        // }
+
+        // [Fact]
+        // public void It_Resolves_AppBase_Commands_Correctly()
+        // {
+        //     var testCommandPath = CreateTestCommandFile(AppContext.BaseDirectory, ".exe", "scriptappbasecommand");
+        //     var testCommandName = Path.GetFileNameWithoutExtension(testCommandPath);
+
+        //     var scriptCommandResolver = new ScriptCommandResolver();
+
+        //     var commandResolverArgs = new CommandResolverArguments
+        //     {
+        //         CommandName = testCommandName,
+        //         CommandArguments = new string[] {}, 
+        //         Environment = new EnvironmentProvider()
+        //     };
+
+        //     var commandSpec = scriptCommandResolver.Resolve(commandResolverArgs);
+        //     commandSpec.Should().NotBeNull();
+
+        //     commandSpec.Path.Should().Be(testCommandPath);
+        //     commandSpec.ResolutionStrategy.Should().Be(CommandResolutionStrategy.BaseDirectory);
+        // }
+
+        // [Fact]
+        // public void It_Resolves_PATH_Commands_Correctly()
+        // {
+        //     var path = Path.Combine(AppContext.BaseDirectory, "pathdir");
+        //     var testCommandPath = CreateTestCommandFile(path, ".dll", "scriptpathcommmand");
+        //     var testCommandName = Path.GetFileNameWithoutExtension(testCommandPath);
+
+        //     Mock<IEnvironmentProvider> mockEnvironment = new Mock<IEnvironmentProvider>();
+        //     mockEnvironment.Setup(c => c
+        //         .GetCommandPath(It.IsAny<string>(), It.IsAny<string[]>()))
+        //         .Returns(testCommandPath);
+
+        //     var scriptCommandResolver = new ScriptCommandResolver();
+
+        //     var commandResolverArgs = new CommandResolverArguments
+        //     {
+        //         CommandName = testCommandName,
+        //         CommandArguments = new string[] {}, 
+        //         Environment = mockEnvironment.Object
+        //     };
+
+        //     var commandSpec = scriptCommandResolver.Resolve(commandResolverArgs);
+        //     commandSpec.Should().NotBeNull();
+
+        //     commandSpec.Path.Should().Be(testCommandPath);
+        //     commandSpec.ResolutionStrategy.Should().Be(CommandResolutionStrategy.Path);
+        // }
+
+        // [Fact]
+        // public void It_does_NOT_Resolve_Project_Tools_Commands()
+        // {
+        //     var testAppPath = Path.Combine(AppContext.BaseDirectory, 
+        //         "TestAssets/TestProjects/AppWithToolDependency");
+
+        //     var scriptCommandResolver = new ScriptCommandResolver();
+
+        //     var commandResolverArgs = new CommandResolverArguments
+        //     {
+        //         CommandName = "dotnet-hello",
+        //         CommandArguments = new string[] {}, 
+        //         ProjectDirectory = testAppPath,
+        //         Environment = new EnvironmentProvider()
+        //     };
+
+        //     var commandSpec = scriptCommandResolver.Resolve(commandResolverArgs);
+        //     commandSpec.Should().BeNull();
+        // }
+
+        // [Fact]
+        // public void It_does_NOT_Resolve_Project_Dependencies_Commands()
+        // {
+        //     var testAppPath = Path.Combine(AppContext.BaseDirectory, 
+        //         "TestAssets/TestProjects/AppWithDirectDependency");
+
+        //     var scriptCommandResolver = new ScriptCommandResolver();
+
+        //     var commandResolverArgs = new CommandResolverArguments
+        //     {
+        //         CommandName = "dotnet-hello",
+        //         CommandArguments = new string[] {}, 
+        //         ProjectDirectory = testAppPath,
+        //         Environment = new EnvironmentProvider(),
+        //         Framework = FrameworkConstants.CommonFrameworks.DnxCore50,
+        //         Configuration = "Debug"
+        //     };
+
+
+        //     var commandSpec = scriptCommandResolver.Resolve(commandResolverArgs);
+        //     commandSpec.Should().BeNull();
+        // }
+
+        // [Fact]
+        // public void It_resolves_ProjectLocal_commands_correctly()
+        // {
+        //     var path = Path.Combine(AppContext.BaseDirectory, 
+        //         "testdir");
+
+        //     var testCommandPath = CreateTestCommandFile(path, ".exe", "scriptprojectlocalcommand");
+        //     var testCommandName = Path.GetFileNameWithoutExtension(testCommandPath);
+
+        //     var scriptCommandResolver = new ScriptCommandResolver();
+
+        //     var commandResolverArgs = new CommandResolverArguments
+        //     {
+        //         CommandName = testCommandName,
+        //         CommandArguments = new string[] {}, 
+        //         ProjectDirectory = path,
+        //         Environment = new EnvironmentProvider()
+        //     };
+
+        //     var commandSpec = scriptCommandResolver.Resolve(commandResolverArgs);
+
+        //     commandSpec.Should().NotBeNull();
+        //     commandSpec.Path.Should().Be(testCommandPath);
+        //     commandSpec.ResolutionStrategy.Should().Be(CommandResolutionStrategy.ProjectLocal);
+
+        // }
+
+        // public string CreateTestCommandFile(string path, string extension, string name = "testcommand")
+        // {
+        //     Directory.CreateDirectory(path);
+
+        //     var filename = name + extension;
+        //     var filepath = Path.Combine(path, filename);
+
+        //     File.WriteAllText(filepath, "hello world");
+
+        //     return filepath;
+        // }
+    }
+}

test/Microsoft.DotNet.Cli.Utils.Tests/GivenAnAppBaseCommandResolver.cs

@@ -0,0 +1,184 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Linq;
+using Xunit;
+using Moq;
+using Microsoft.DotNet.Cli.Utils;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.Tools.Test.Utilities;
+using Microsoft.Extensions.PlatformAbstractions;
+using System.Threading;
+using FluentAssertions;
+using NuGet.Frameworks;
+
+namespace Microsoft.DotNet.Cli.Utils.Tests
+{
+    public class GivenAnAppBaseCommandResolver
+    {
+        [Fact]
+        public void It_returns_null_when_CommandName_is_null()
+        {
+            var appBaseCommandResolver = SetupPlatformAppBaseCommandResolver();
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = null,
+                CommandArguments = null
+            };
+
+            var result = appBaseCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().BeNull();
+        }
+
+        [Fact]
+        public void It_returns_null_when_CommandName_does_not_exist_applocal()
+        {
+            var appBaseCommandResolver = SetupPlatformAppBaseCommandResolver();
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "nonexistent-command",
+                CommandArguments = null
+            };
+
+            var result = appBaseCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().BeNull();
+        }
+
+        [Fact]
+        public void It_returns_a_CommandSpec_with_CommandName_as_FileName_when_CommandName_exists_applocal()
+        {
+            var environment = CommandResolverTestUtils.SetupEnvironmentProviderWhichFindsExtensions(".exe");
+            var appBaseCommandResolver = SetupPlatformAppBaseCommandResolver(environment);
+
+            CommandResolverTestUtils.CreateNonRunnableTestCommand(AppContext.BaseDirectory, "appbasetestcommand1", ".exe");
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "appbasetestcommand1",
+                CommandArguments = null
+            };
+
+            var result = appBaseCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().NotBeNull();
+
+            var commandFile = Path.GetFileNameWithoutExtension(result.Path);
+
+            commandFile.Should().Be("appbasetestcommand1");
+        }
+
+        [Fact]
+        public void It_returns_null_when_CommandName_exists_applocal_in_a_subdirectory()
+        {
+            var environment = CommandResolverTestUtils.SetupEnvironmentProviderWhichFindsExtensions(".exe");
+            var appBaseCommandResolver = SetupPlatformAppBaseCommandResolver(environment);
+
+            var testDir = Path.Combine(AppContext.BaseDirectory, "appbasetestsubdir");
+            CommandResolverTestUtils.CreateNonRunnableTestCommand(testDir, "appbasetestsubdircommand", ".exe");
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "appbasetestsubdircommand",
+                CommandArguments = null
+            };
+
+            var result = appBaseCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().BeNull();
+        }
+
+        [Fact]
+        public void It_escapes_CommandArguments_when_returning_a_CommandSpec()
+        {
+            var environment = CommandResolverTestUtils.SetupEnvironmentProviderWhichFindsExtensions(".exe");
+            var appBaseCommandResolver = SetupPlatformAppBaseCommandResolver(environment);
+
+            CommandResolverTestUtils.CreateNonRunnableTestCommand(AppContext.BaseDirectory, "appbasetestcommand1", ".exe");
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "appbasetestcommand1",
+                CommandArguments = new [] { "arg with space"}
+            };
+
+            var result = appBaseCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().NotBeNull();
+            result.Args.Should().Be("\"arg with space\"");
+        }
+
+        [Fact]
+        public void It_returns_a_CommandSpec_with_Args_as_stringEmpty_when_returning_a_CommandSpec_and_CommandArguments_are_null()
+        {
+            var environment = CommandResolverTestUtils.SetupEnvironmentProviderWhichFindsExtensions(".exe");
+            var appBaseCommandResolver = SetupPlatformAppBaseCommandResolver(environment);
+
+            CommandResolverTestUtils.CreateNonRunnableTestCommand(AppContext.BaseDirectory, "appbasetestcommand1", ".exe");
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "appbasetestcommand1",
+                CommandArguments = null
+            };
+
+            var result = appBaseCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().NotBeNull();
+            result.Args.Should().Be(string.Empty);
+        }
+
+        [Fact]
+        public void It_prefers_EXE_over_CMD_when_two_command_candidates_exist_and_using_WindowsExePreferredCommandSpecFactory()
+        {
+            var environment = CommandResolverTestUtils.SetupEnvironmentProviderWhichFindsExtensions(".exe");
+            var platformCommandSpecFactory = new WindowsExePreferredCommandSpecFactory();
+
+            var appBaseCommandResolver = new AppBaseCommandResolver(environment, platformCommandSpecFactory);
+
+            CommandResolverTestUtils.CreateNonRunnableTestCommand(AppContext.BaseDirectory, "appbasetestcommand1", ".exe");
+            CommandResolverTestUtils.CreateNonRunnableTestCommand(AppContext.BaseDirectory, "appbasetestcommand1", ".cmd");
+
+            var commandResolverArguments = new CommandResolverArguments()
+            {
+                CommandName = "appbasetestcommand1",
+                CommandArguments = null
+            };
+
+            var result = appBaseCommandResolver.Resolve(commandResolverArguments);
+
+            result.Should().NotBeNull();
+
+            var commandFile = Path.GetFileName(result.Path);
+            commandFile.Should().Be("appbasetestcommand1.exe");
+        }
+
+        private AppBaseCommandResolver SetupPlatformAppBaseCommandResolver(IEnvironmentProvider environment = null)
+        {
+            environment = environment ?? new EnvironmentProvider();
+
+            var platformCommandSpecFactory = default(IPlatformCommandSpecFactory);
+
+            if (PlatformServices.Default.Runtime.OperatingSystemPlatform == Platform.Windows)
+            {
+                platformCommandSpecFactory = new WindowsExePreferredCommandSpecFactory();
+            }
+            else
+            {
+                platformCommandSpecFactory = new GenericPlatformCommandSpecFactory();
+            }
+
+            var appBaseCommandResolver = new AppBaseCommandResolver(environment, platformCommandSpecFactory);
+
+            return appBaseCommandResolver;
+        }
+    }
+}

test/Microsoft.DotNet.Cli.Utils.Tests/project.json

@@ -13,6 +13,7 @@
 
         "Microsoft.DotNet.Tools.Tests.Utilities": { "target": "project" },
         
+        "moq.netcore": "4.4.0-beta8",
         "xunit": "2.1.0",
         "dotnet-test-xunit": "1.0.0-dev-79755-47"
     },
@@ -27,7 +28,11 @@
     },
 
     "content": [
-        "../../TestAssets/TestProjects/OutputStandardOutputAndError/*"
+        "../../TestAssets/TestProjects/OutputStandardOutputAndError/*",
+        "../../TestAssets/TestProjects/TestAppWithArgs/*",
+        "../../TestAssets/TestProjects/AppWithDirectAndToolDependency/**/*",
+        "../../TestAssets/TestProjects/AppWithDirectDependency/**/*",
+        "../../TestAssets/TestProjects/AppWithToolDependency/**/*"
     ],
 
     "testRunner": "xunit"