Reapply "[build] Track glob dependencies via depfiles, instead of always re-executing scripts at GN time."

Use a relative path for the depfile's target to match Ninja's expectation; otherwise it thinks the target is always dirty.

TEST=build twice
Bug: https://github.com/flutter/flutter/issues/81074
Change-Id: I4cae7ab55f79b5206521c7090502c0769d2b5277
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/198443
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

tools/create_timestamp_file.py

@@ -1,19 +0,0 @@
-#!/usr/bin/env python3
-# Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
-# for details. All rights reserved. Use of this source code is governed by a
-# BSD-style license that can be found in the LICENSE file.
-
-import sys
-import os
-
-
-def main(args):
-    for file_name in args[1:]:
-        dir_name = os.path.dirname(file_name)
-        if not os.path.exists(dir_name):
-            os.mkdir(dir_name)
-        open(file_name, 'w').close()
-
-
-if __name__ == '__main__':
-    sys.exit(main(sys.argv))

tools/list_dart_files_as_depfile.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+# Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+"""Tool for listing Dart source files.
+
+If the first argument is 'relative', the script produces paths relative to the
+current working directory. If the first argument is 'absolute', the script
+produces absolute paths.
+
+Usage:
+  python3 tools/list_dart_files_as_depfile.py <depfile> <directory> <pattern>
+"""
+
+import os
+import re
+import sys
+
+
+def main(argv):
+    depfile = argv[1]
+    directory = argv[2]
+    if not os.path.isabs(directory):
+        directory = os.path.realpath(directory)
+
+    pattern = None
+    if len(argv) > 3:
+        pattern = re.compile(argv[3])
+
+    # Output a GN/Ninja depfile, whose format is a Makefile with one target.
+    out = open(depfile, 'w')
+    out.write(os.path.relpath(depfile))
+    out.write(":")
+
+    for root, directories, files in os.walk(directory):
+        # We only care about actual source files, not generated code or tests.
+        for skip_dir in ['.git', 'gen', 'test']:
+            if skip_dir in directories:
+                directories.remove(skip_dir)
+
+        # If we are looking at the root directory, filter the immediate
+        # subdirectories by the given pattern.
+        if pattern and root == directory:
+            directories[:] = filter(pattern.match, directories)
+
+        for filename in files:
+            if filename.endswith(
+                    '.dart') and not filename.endswith('_test.dart'):
+                fullname = os.path.join(directory, root, filename)
+                fullname = fullname.replace(os.sep, '/')
+                out.write(" \"")
+                out.write(fullname)
+                out.write("\"")
+
+    out.write("\n")
+    out.close()
+
+
+if __name__ == '__main__':
+    sys.exit(main(sys.argv))

utils/create_timestamp.gni

@@ -10,16 +10,15 @@ template("create_timestamp_file") {
   path = invoker.path
   output = invoker.output
   action(target_name) {
-    list_args = [ path ]
+    script = "$_dart_root/tools/list_dart_files_as_depfile.py"
+    args = [
+      rebase_path(output),
+      path,
+    ]
     if (defined(invoker.pattern)) {
-      list_args += [ invoker.pattern ]
+      args += [ invoker.pattern ]
     }
-    files = exec_script("$_dart_root/tools/list_dart_files.py",
-                        [ "absolute" ] + list_args,
-                        "list lines")
-    inputs = [ "$_dart_root/tools/list_dart_files.py" ] + files
+    depfile = output
     outputs = [ output ]
-    script = "$_dart_root/tools/create_timestamp_file.py"
-    args = [ rebase_path(output) ]
   }
 }