refactor: auto generate electron_version.h from the version file (#18866)

* refactor: auto generate electron_version.h from the version file

* Update BUILD.gn

Co-Authored-By: Jeremy Apthorp <nornagon@nornagon.net>

build/generate-template.py

@@ -0,0 +1,16 @@
+import json
+import sys
+from string import Template
+
+inpath = sys.argv[1]
+outpath = sys.argv[2]
+argpaths = sys.argv[3:]
+
+with open(inpath, 'r') as infile, open(outpath, 'w') as outfile:
+  data = {}
+  for argpath in argpaths:
+    with open(argpath, 'r') as argfile:
+      data.update(json.load(argfile))
+
+  s =  Template(infile.read()).substitute(data)
+  outfile.write(s)

build/templated_file.gni

@@ -0,0 +1,39 @@
+template("templated_file") {
+  assert(defined(invoker.template), "Need template file to run")
+  assert(defined(invoker.output), "Need output file to run")
+
+  if (defined(invoker.values)) {
+    args_path = "$target_gen_dir/$target_name.args"
+    write_file(args_path, invoker.values, "json")
+  }
+
+  action(target_name) {
+    forward_variables_from(invoker,
+                           [
+                             "deps",
+                             "public_deps",
+                             "inputs",
+                             "outputs",
+                           ])
+    inputs = [
+      invoker.template,
+    ]
+    outputs = [
+      invoker.output,
+    ]
+    script = "//electron/build/generate-template.py"
+    args = [
+      rebase_path(invoker.template),
+      rebase_path(invoker.output),
+    ]
+
+    if (defined(invoker.values)) {
+      args += rebase_path(args_path)
+    }
+
+    if (defined(invoker.args_files)) {
+      args += rebase_path(invoker.args_files)
+      inputs += invoker.args_files
+    }
+  }
+}

build/templates/electron_version.tmpl

@@ -0,0 +1,23 @@
+// Copyright (c) 2019 Slack Technologies, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#ifndef ELECTRON_ELECTRON_VERSION_H
+#define ELECTRON_ELECTRON_VERSION_H
+
+#define ELECTRON_MAJOR_VERSION $major
+#define ELECTRON_MINOR_VERSION $minor
+#define ELECTRON_PATCH_VERSION $patch
+#if $has_prerelease
+#define ELECTRON_PRE_RELEASE_VERSION -$prerelease
+#endif
+
+#ifndef ELECTRON_PRE_RELEASE_VERSION
+#define ELECTRON_VERSION_STRING "$major.$minor.$patch"
+#else
+#define ELECTRON_VERSION_STRING "$major.$minor.$patch-$prerelease"
+#endif
+
+#define ELECTRON_VERSION "v" ELECTRON_VERSION_STRING
+
+#endif  // ELECTRON_ELECTRON_VERSION_H