Update gn_helpers.py from upstream (flutter#493)

Updates our ToGNString implementation to match the Chromium version at
version 4e21091c52ffc65be4df7839cc2e86575237e968 of the upstream repo
https://chromium.googlesource.com/chromium/src/+/refs/heads/main/build/gn_helpers.py

Also switches to absolute (buildroot relative) paths for invocations of
vs_toolchain.py.

build/config/win/visual_studio_version.gni

@@ -24,7 +24,7 @@ declare_args() {
 
 if (visual_studio_path == "") {
   _toolchain_data =
-      exec_script("../../vs_toolchain.py", [ "get_toolchain_dir" ], "scope")
+      exec_script("//build/vs_toolchain.py", [ "get_toolchain_dir" ], "scope")
   visual_studio_path = _toolchain_data.vs_path
   windows_sdk_path = _toolchain_data.sdk_path
   visual_studio_version = _toolchain_data.vs_version

build/gn_helpers.py

@@ -2,38 +2,132 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import sys
+
 """Helper functions useful when writing scripts that are run from GN's
 exec_script function."""
 
-class GNException(Exception):
+class GNError(Exception):
   pass
 
 
-def ToGNString(value, allow_dicts = True):
-  """Prints the given value to stdout.
+# Computes ASCII code of an element of encoded Python 2 str / Python 3 bytes.
+_Ord = ord if sys.version_info.major < 3 else lambda c: c
+
+
+def _TranslateToGnChars(s):
+  for decoded_ch in s.encode('utf-8'):  # str in Python 2, bytes in Python 3.
+    code = _Ord(decoded_ch)  # int
+    if code in (34, 36, 92):  # For '"', '$', or '\\'.
+      yield '\\' + chr(code)
+    elif 32 <= code < 127:
+      yield chr(code)
+    else:
+      yield '$0x%02X' % code
+
+
+def ToGNString(value, pretty=False):
+  """Returns a stringified GN equivalent of a Python value.
+
+  Args:
+    value: The Python value to convert.
+    pretty: Whether to pretty print. If true, then non-empty lists are rendered
+        recursively with one item per line, with indents. Otherwise lists are
+        rendered without new line.
+  Returns:
+    The stringified GN equivalent to |value|.
+
+  Raises:
+    GNError: |value| cannot be printed to GN.
+  """
+
+  if sys.version_info.major < 3:
+    basestring_compat = basestring
+  else:
+    basestring_compat = str
+
+  # Emits all output tokens without intervening whitespaces.
+  def GenerateTokens(v, level):
+    if isinstance(v, basestring_compat):
+      yield '"' + ''.join(_TranslateToGnChars(v)) + '"'
+
+    elif isinstance(v, bool):
+      yield 'true' if v else 'false'
+
+    elif isinstance(v, int):
+      yield str(v)
+
+    elif isinstance(v, list):
+      yield '['
+      for i, item in enumerate(v):
+        if i > 0:
+          yield ','
+        for tok in GenerateTokens(item, level + 1):
+          yield tok
+      yield ']'
+
+    elif isinstance(v, dict):
+      if level > 0:
+        yield '{'
+      for key in sorted(v):
+        if not isinstance(key, basestring_compat):
+          raise GNError('Dictionary key is not a string.')
+        if not key or key[0].isdigit() or not key.replace('_', '').isalnum():
+          raise GNError('Dictionary key is not a valid GN identifier.')
+        yield key  # No quotations.
+        yield '='
+        for tok in GenerateTokens(v[key], level + 1):
+          yield tok
+      if level > 0:
+        yield '}'
+
+    else:  # Not supporting float: Add only when needed.
+      raise GNError('Unsupported type when printing to GN.')
 
-  allow_dicts indicates if this function will allow converting dictionaries
-  to GN scopes. This is only possible at the top level, you can't nest a
-  GN scope in a list, so this should be set to False for recursive calls."""
-  if isinstance(value, str) or isinstance(value, str):
-    if value.find('\n') >= 0:
-      raise GNException("Trying to print a string with a newline in it.")
-    return '"' + value.replace('"', '\\"') + '"'
+  can_start = lambda tok: tok and tok not in ',}]='
+  can_end = lambda tok: tok and tok not in ',{[='
 
-  if isinstance(value, list):
-    return '[ %s ]' % ', '.join(ToGNString(v) for v in value)
+  # Adds whitespaces, trying to keep everything (except dicts) in 1 line.
+  def PlainGlue(gen):
+    prev_tok = None
+    for i, tok in enumerate(gen):
+      if i > 0:
+        if can_end(prev_tok) and can_start(tok):
+          yield '\n'  # New dict item.
+        elif prev_tok == '[' and tok == ']':
+          yield '  '  # Special case for [].
+        elif tok != ',':
+          yield ' '
+      yield tok
+      prev_tok = tok
 
-  if isinstance(value, dict):
-    if not allow_dicts:
-      raise GNException("Attempting to recursively print a dictionary.")
-    result = ""
-    for key in value:
-      if not isinstance(key, str):
-        raise GNException("Dictionary key is not a string.")
-      result += "%s = %s\n" % (key, ToGNString(value[key], False))
-    return result
+  # Adds whitespaces so non-empty lists can span multiple lines, with indent.
+  def PrettyGlue(gen):
+    prev_tok = None
+    level = 0
+    for i, tok in enumerate(gen):
+      if i > 0:
+        if can_end(prev_tok) and can_start(tok):
+          yield '\n' + '  ' * level  # New dict item.
+        elif tok == '=' or prev_tok in '=':
+          yield ' '  # Separator before and after '=', on same line.
+      if tok in ']}':
+        level -= 1
+      # Exclude '[]' and '{}' cases.
+      if int(prev_tok == '[') + int(tok == ']') == 1 or \
+         int(prev_tok == '{') + int(tok == '}') == 1:
+        yield '\n' + '  ' * level
+      yield tok
+      if tok in '[{':
+        level += 1
+      if tok == ',':
+        yield '\n' + '  ' * level
+      prev_tok = tok
 
-  if isinstance(value, int):
-    return str(value)
+  token_gen = GenerateTokens(value, 0)
+  ret = ''.join((PrettyGlue if pretty else PlainGlue)(token_gen))
+  # Add terminating '\n' for dict |value| or multi-line output.
+  if isinstance(value, dict) or '\n' in ret:
+    return ret + '\n'
+  return ret
 
-  raise GNException("Unsupported type %s (value %s) when printing to GN." % (type(value), value))

build/toolchain/win/BUILD.gn

@@ -56,7 +56,7 @@ if (current_toolchain == default_toolchain) {
   } else {
     configuration = "Release"
   }
-  exec_script("../../vs_toolchain.py",
+  exec_script("//build/vs_toolchain.py",
               [
                 "copy_dlls",
                 rebase_path(root_build_dir),