Reland "Add comment at the top of auto generated files"

This is a reland of 2c5431c5

Additionally Modified Logic by prepending comment with contents
in order to avoid Deterministic Linux Build Infra fail

Original change's description:
> Add comment at the top of auto generated files
>
> Add comment like "// this file is autogenerated, do not edit"
> at the top of the files generated from .mojom files
>
>
> Bug: 609794
> Change-Id: I1b39afc0d7c054510f7446af8795e606f07fdfdb
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1757406
> Reviewed-by: Ken Rockot <rockot@google.com>
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Commit-Queue: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#689608}

Bug: 609794
Change-Id: I579fa81f36385e02e939742cefbf39289ca1ef50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1775653Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#691679}

mojo/public/tools/bindings/generators/mojom_cpp_generator.py

@@ -438,30 +438,31 @@ class Generator(generator.Generator):
 
     if self.generate_non_variant_code:
       if self.generate_message_ids:
-        self.Write(self._GenerateModuleSharedMessageIdsHeader(),
+        self.WriteWithComment(self._GenerateModuleSharedMessageIdsHeader(),
                               "%s-shared-message-ids.h" % self.module.path)
       else:
-        self.Write(self._GenerateModuleSharedHeader(),
+        self.WriteWithComment(self._GenerateModuleSharedHeader(),
                               "%s-shared.h" % self.module.path)
-        self.Write(self._GenerateModuleSharedInternalHeader(),
+        self.WriteWithComment(self._GenerateModuleSharedInternalHeader(),
                               "%s-shared-internal.h" % self.module.path)
-        self.Write(self._GenerateModuleSharedSource(),
+        self.WriteWithComment(self._GenerateModuleSharedSource(),
                               "%s-shared.cc" % self.module.path)
-        self.Write(self._GenerateModuleParamsDataHeader(),
+        self.WriteWithComment(self._GenerateModuleParamsDataHeader(),
                               "%s-params-data.h" % self.module.path)
     else:
       suffix = "-%s" % self.variant if self.variant else ""
-      self.Write(self._GenerateModuleHeader(),
+      self.WriteWithComment(self._GenerateModuleHeader(),
                             "%s%s.h" % (self.module.path, suffix))
-      self.Write(self._GenerateModuleForwardHeader(),
+      self.WriteWithComment(self._GenerateModuleForwardHeader(),
                             "%s%s-forward.h" % (self.module.path, suffix))
-      self.Write(self._GenerateModuleSource(),
+      self.WriteWithComment(self._GenerateModuleSource(),
                             "%s%s.cc" % (self.module.path, suffix))
-      self.Write(self._GenerateModuleImportHeadersHeader(),
-                 "%s%s-import-headers.h" % (self.module.path, suffix))
-      self.Write(self._GenerateModuleTestUtilsHeader(),
+      self.WriteWithComment(self._GenerateModuleImportHeadersHeader(),
+                            "%s%s-import-headers.h" % (self.module.path,
+                                                       suffix))
+      self.WriteWithComment(self._GenerateModuleTestUtilsHeader(),
                             "%s%s-test-utils.h" % (self.module.path, suffix))
-      self.Write(self._GenerateModuleTestUtilsSource(),
+      self.WriteWithComment(self._GenerateModuleTestUtilsSource(),
                             "%s%s-test-utils.cc" % (self.module.path, suffix))
 
   def _ConstantValue(self, constant):

mojo/public/tools/bindings/generators/mojom_java_generator.py

@@ -521,25 +521,25 @@ class Generator(generator.Generator):
     fileutil.EnsureDirectoryExists(self.output_dir)
 
     for struct in self.module.structs:
-      self.Write(self._GenerateStructSource(struct),
+      self.WriteWithComment(self._GenerateStructSource(struct),
                             '%s.java' % GetNameForElement(struct))
 
     for union in self.module.unions:
-      self.Write(self._GenerateUnionSource(union),
+      self.WriteWithComment(self._GenerateUnionSource(union),
                             '%s.java' % GetNameForElement(union))
 
     for enum in self.module.enums:
-      self.Write(self._GenerateEnumSource(enum),
+      self.WriteWithComment(self._GenerateEnumSource(enum),
                             '%s.java' % GetNameForElement(enum))
 
     for interface in self.module.interfaces:
-      self.Write(self._GenerateInterfaceSource(interface),
+      self.WriteWithComment(self._GenerateInterfaceSource(interface),
                             '%s.java' % GetNameForElement(interface))
-      self.Write(self._GenerateInterfaceInternalSource(interface),
+      self.WriteWithComment(self._GenerateInterfaceInternalSource(interface),
                             '%s_Internal.java' % GetNameForElement(interface))
 
     if self.module.constants:
-      self.Write(self._GenerateConstantsSource(self.module),
+      self.WriteWithComment(self._GenerateConstantsSource(self.module),
                             '%s.java' % GetConstantsMainEntityName(self.module))
 
   def GenerateFiles(self, unparsed_args):

mojo/public/tools/bindings/generators/mojom_js_generator.py

@@ -364,12 +364,15 @@ class Generator(generator.Generator):
     # affected and we can remove this method.
     self._SetUniqueNameForImports()
 
-    self.Write(self._GenerateAMDModule(), "%s.js" % self.module.path)
-    self.Write(self._GenerateExterns(), "%s.externs.js" % self.module.path)
+    self.WriteWithComment(self._GenerateAMDModule(), "%s.js" % self.module.path)
+    self.WriteWithComment(self._GenerateExterns(),
+                          "%s.externs.js" % self.module.path)
     if self.js_bindings_mode == "new":
-      self.Write(self._GenerateLiteHtml(), "%s.html" % self.module.path)
-      self.Write(self._GenerateLiteBindings(), "%s-lite.js" % self.module.path)
-      self.Write(self._GenerateLiteBindingsForCompile(),
+      self.WriteWithComment(self._GenerateLiteHtml(),
+                            "%s.html" % self.module.path)
+      self.WriteWithComment(self._GenerateLiteBindings(),
+                            "%s-lite.js" % self.module.path)
+      self.WriteWithComment(self._GenerateLiteBindingsForCompile(),
                             "%s-lite-for-compile.js" % self.module.path)
 
   def _SetUniqueNameForImports(self):

mojo/public/tools/bindings/pylib/mojom/generate/generator.py

@@ -197,6 +197,14 @@ class Generator(object):
     full_path = os.path.join(self.output_dir, filename)
     WriteFile(contents, full_path)
 
+  def WriteWithComment(self, contents, filename):
+    generator_name = "mojom_bindings_generator.py"
+    comment = r"// %s is auto generated by %s, do not edit" % (filename,
+                                                               generator_name)
+
+    contents = comment + '\n' + '\n' + contents;
+    self.Write(contents, filename)
+
   def GenerateFiles(self, args):
     raise NotImplementedError("Subclasses must override/implement this method")