support fuzzy matching of addon commands

Note this does find things in PATH that are not executable.
Like searchPath use, the executable bit is not checked. Thing is,
there does not seem to be a binding for access(), which would be the
right way to check that the right execute bit is set. Anyway, if it's in
PATH and it's a file, it's probably fine to treat it as something that
was intended to be executable.

This commit was sponsored by Brock Spratlen on Patreon.

CmdLine.hs

@@ -33,8 +33,8 @@ dispatch :: Bool -> Bool -> CmdParams -> [Command] -> [(String, String)] -> IO G
 dispatch addonok fuzzyok allargs allcmds fields getgitrepo progname progdesc =
 	go addonok allcmds $
 		findAddonCommand subcommandname >>= \case
-			Nothing -> go False allcmds noop
-			Just c -> go addonok (c:allcmds) $
+			Just c -> go addonok (c:allcmds) noop
+			Nothing -> go addonok allcmds $
 				findAllAddonCommands >>= \cs ->
 					go False (cs++allcmds) noop
   where
@@ -158,7 +158,20 @@ findAddonCommand (Just subcommandname) =
 	c = "git-annex-" ++ subcommandname
 
 findAllAddonCommands :: IO [Command]
-findAllAddonCommands = return [] -- TODO
+findAllAddonCommands = 
+	filter isaddoncommand
+		. map (\p -> mkAddonCommand p (deprefix p))
+		<$> searchPathContents ("git-annex-" `isPrefixOf`)
+  where
+	deprefix = replace "git-annex-" "" . takeFileName
+	isaddoncommand c
+		-- git-annex-shell
+		| cmdname c == "shell" = False
+		-- external special remotes
+		| "remote-" `isPrefixOf` cmdname c = False
+		-- external backends
+		| "backend-" `isPrefixOf` cmdname c = False
+		| otherwise = True
 
 mkAddonCommand :: FilePath -> String -> Command
 mkAddonCommand p subcommandname = Command

Utility/Path.hs

@@ -31,6 +31,7 @@ import qualified System.FilePath as P
 import qualified Data.ByteString as B
 import Data.List
 import Data.Maybe
+import Control.Monad
 import Control.Applicative
 import Prelude
 
@@ -218,9 +219,14 @@ searchPath command
 
 {- Finds commands in PATH that match a predicate. Note that the predicate
  - matches on the basename of the command, but the full path to it is
- - returned. -}
+ - returned.
+ -
+ - Note that this will find commands in PATH that are not executable.
+ -}
 searchPathContents :: (FilePath -> Bool) -> IO [FilePath]
-searchPathContents p = concat <$> (P.getSearchPath >>= mapM go)
+searchPathContents p =
+	filterM doesFileExist 
+		=<< (concat <$> (P.getSearchPath >>= mapM go))
   where
 	go d = map (d P.</>) . filter p
 		<$> catchDefaultIO [] (getDirectoryContents d)