[ios] Fix interaction of build/clobber.py & ios/build/tools/setup-gn.py

The script build/clobber.py tried to parse the build.ninja when
clobbering a directory and use it as a template, however if the
parsing failed, it generated a broken build.ninja file.

The script ios/build/tools/setup-gn.py would create multiple
empty build directory with just args.gn and a build.ninja file
that would result in invoking `gn gen` as a first step.

However, the build.ninja created by setup-gn.py could not be
parsed by clobber.py since it did not include minimum required
version of ninja command. Also, setup-gn.py did not recreate
the file if they existed, even if they were incorrect.

All this caused build/clobber.py to sometimes leave a build
directory in an unbuildable state requiring the developer to
run `gn gen` manually.

To fix this, change setup-gn.py to always overwrite build.ninja
file, to use a format that can be parsed by clobber.py and fix
clobber.py to write a build.ninja file that is valid if parsing
fails.

Always overwrite the build.ninja file to ensure that `--check`
is added to `gn gen` invocation (as locally running `gn gen`
without `--check` even once would disable the local check of the
deps and later be reported by Chrome iOS developers as a bug).

Bug: 1102331
Change-Id: Iabe906ac5f676f1b837c6ebb03ee32d73c7b6cf9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2283143
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786208}

build/clobber.py

@@ -89,13 +89,15 @@ def delete_build_dir(build_dir):
       f.write(build_commands)
     else:
       # Couldn't parse the build.ninja file, write a default thing.
-      f.write('''rule gn
-command = gn -q gen //out/%s/
-description = Regenerating ninja files
+      f.write('''ninja_required_version = 1.7.2
+
+rule gn
+  command = gn -q gen //out/%s/
+  description = Regenerating ninja files
 
 build build.ninja: gn
-generator = 1
-depfile = build.ninja.d
+  generator = 1
+  depfile = build.ninja.d
 ''' % (os.path.split(build_dir)[1]))
 
   # Write a .d file for the build which references a nonexistant file. This

ios/build/tools/setup-gn.py

@@ -126,83 +126,65 @@ class GnGenerator(object):
     return args
 
 
-  def Generate(self, gn_path, root_path, out_path):
-    buf = io.StringIO()
-    self.WriteArgsGn(buf)
-    WriteToFileIfChanged(
-        os.path.join(out_path, 'args.gn'),
-        buf.getvalue(),
-        overwrite=True)
-
+  def Generate(self, gn_path, root_path, build_dir):
+    self.WriteArgsGn(build_dir)
     subprocess.check_call(
-        self.GetGnCommand(gn_path, root_path, out_path, True))
-
-  def CreateGnRules(self, gn_path, root_path, out_path):
-    buf = io.StringIO()
-    self.WriteArgsGn(buf)
-    WriteToFileIfChanged(
-        os.path.join(out_path, 'args.gn'),
-        buf.getvalue(),
-        overwrite=True)
-
-    buf = io.StringIO()
-    gn_command = self.GetGnCommand(gn_path, root_path, out_path, False)
-    self.WriteBuildNinja(buf, gn_command)
-    WriteToFileIfChanged(
-        os.path.join(out_path, 'build.ninja'),
-        buf.getvalue(),
-        overwrite=False)
-
-    buf = io.StringIO()
-    self.WriteBuildNinjaDeps(buf)
-    WriteToFileIfChanged(
-        os.path.join(out_path, 'build.ninja.d'),
-        buf.getvalue(),
-        overwrite=False)
-
-  def WriteArgsGn(self, stream):
-    stream.write('# This file was generated by setup-gn.py. Do not edit\n')
-    stream.write('# but instead use ~/.setup-gn or $repo/.setup-gn files\n')
-    stream.write('# to configure settings.\n')
-    stream.write('\n')
-
-    if self._settings.has_section('$imports$'):
-      for import_rule in self._settings.values('$imports$'):
-        stream.write('import("%s")\n' % import_rule)
+        self.GetGnCommand(gn_path, root_path, build_dir, True))
+
+  def CreateGnRules(self, gn_path, root_path, build_dir):
+    gn_command = self.GetGnCommand('gn', root_path, build_dir, False)
+    self.WriteArgsGn(build_dir)
+    self.WriteBuildNinja(gn_command, build_dir)
+    self.WriteBuildNinjaDeps(build_dir)
+
+  def WriteArgsGn(self, build_dir):
+    with open(os.path.join(build_dir, 'args.gn'), 'w') as stream:
+      stream.write('# This file was generated by setup-gn.py. Do not edit\n')
+      stream.write('# but instead use ~/.setup-gn or $repo/.setup-gn files\n')
+      stream.write('# to configure settings.\n')
       stream.write('\n')
 
-    gn_args = self._GetGnArgs()
-    for name, value in gn_args:
-      if isinstance(value, bool):
-        stream.write('%s = %s\n' % (name, str(value).lower()))
-      elif isinstance(value, list):
-        stream.write('%s = [%s' % (name, '\n' if len(value) > 1 else ''))
-        if len(value) == 1:
-          prefix = ' '
-          suffix = ' '
-        else:
-          prefix = '  '
-          suffix = ',\n'
-        for item in value:
-          if isinstance(item, bool):
-            stream.write('%s%s%s' % (prefix, str(item).lower(), suffix))
+      if self._settings.has_section('$imports$'):
+        for import_rule in self._settings.values('$imports$'):
+          stream.write('import("%s")\n' % import_rule)
+        stream.write('\n')
+
+      gn_args = self._GetGnArgs()
+      for name, value in gn_args:
+        if isinstance(value, bool):
+          stream.write('%s = %s\n' % (name, str(value).lower()))
+        elif isinstance(value, list):
+          stream.write('%s = [%s' % (name, '\n' if len(value) > 1 else ''))
+          if len(value) == 1:
+            prefix = ' '
+            suffix = ' '
           else:
-            stream.write('%s%s%s' % (prefix, item, suffix))
-        stream.write(']\n')
-      else:
-        stream.write('%s = %s\n' % (name, value))
-
-  def WriteBuildNinja(self, stream, gn_command):
-    stream.write('rule gn\n')
-    stream.write('  command = %s\n' % NinjaEscapeCommand(gn_command))
-    stream.write('  description = Regenerating ninja files\n')
-    stream.write('\n')
-    stream.write('build build.ninja: gn\n')
-    stream.write('  generator = 1\n')
-    stream.write('  depfile = build.ninja.d\n')
-
-  def WriteBuildNinjaDeps(self, stream):
-    stream.write('build.ninja: nonexistant_file.gn\n')
+            prefix = '  '
+            suffix = ',\n'
+          for item in value:
+            if isinstance(item, bool):
+              stream.write('%s%s%s' % (prefix, str(item).lower(), suffix))
+            else:
+              stream.write('%s%s%s' % (prefix, item, suffix))
+          stream.write(']\n')
+        else:
+          stream.write('%s = %s\n' % (name, value))
+
+  def WriteBuildNinja(self, gn_command, build_dir):
+    with open(os.path.join(build_dir, 'build.ninja'), 'w') as stream:
+      stream.write('ninja_required_version = 1.7.2\n')
+      stream.write('\n')
+      stream.write('rule gn\n')
+      stream.write('  command = %s\n' % NinjaEscapeCommand(gn_command))
+      stream.write('  description = Regenerating ninja files\n')
+      stream.write('\n')
+      stream.write('build build.ninja: gn\n')
+      stream.write('  generator = 1\n')
+      stream.write('  depfile = build.ninja.d\n')
+
+  def WriteBuildNinjaDeps(self, build_dir):
+    with open(os.path.join(build_dir, 'build.ninja.d'), 'w') as stream:
+      stream.write('build.ninja: nonexistant_file.gn\n')
 
   def GetGnCommand(self, gn_path, src_path, out_path, generate_xcode_project):
     gn_command = [ gn_path, '--root=%s' % os.path.realpath(src_path), '-q' ]
@@ -223,21 +205,6 @@ class GnGenerator(object):
     return gn_command
 
 
-def WriteToFileIfChanged(filename, content, overwrite):
-  '''Write |content| to |filename| if different. If |overwrite| is False
-  and the file already exists it is left untouched.'''
-  if os.path.exists(filename):
-    if not overwrite:
-      return
-    with open(filename) as file:
-      if file.read() == content:
-        return
-  if not os.path.isdir(os.path.dirname(filename)):
-    os.makedirs(os.path.dirname(filename))
-  with open(filename, 'w') as file:
-    file.write(content)
-
-
 def NinjaNeedEscape(arg):
   '''Returns True if |arg| needs to be escaped when written to .ninja file.'''
   return ':' in arg or '*' in arg or ';' in arg
@@ -289,6 +256,9 @@ def GenerateGnBuildRules(gn_path, root_dir, out_dir, settings):
   for config in SUPPORTED_CONFIGS:
     for target in SUPPORTED_TARGETS:
       build_dir = os.path.join(out_dir, '%s-%s' % (config, target))
+      if not os.path.isdir(build_dir):
+        os.makedirs(build_dir)
+
       generator = GnGenerator(settings, config, target)
       generator.CreateGnRules(gn_path, root_dir, build_dir)