Partially reland Auto-generate v8 version based on tags.

build/generate_version.py

Index: build/generate_version.py
diff --git a/build/generate_version.py b/build/generate_version.py
new file mode 100755
index 0000000000000000000000000000000000000000..2d4c40dba3e8de5dc22bee7032515648d2ddfd09
--- /dev/null
+++ b/build/generate_version.py
@@ -0,0 +1,118 @@
+#!/usr/bin/env python
+# Copyright 2014 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""
+Script to set v8's version file to the version given by the latest tag.
+
+The script is intended to be run as a gclient hook. The script will write a
+generated version file into the checkout.
+
+On build systems where no git is available and where the version information
+is not necessary, the version generation can be bypassed with the option
+--skip.
+"""
+
+
+import optparse
+import os
+import re
+import subprocess
+import sys
+
+
+CWD = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
+VERSION_CC = os.path.join(CWD, "src", "version.cc")
+VERSION_GEN_CC = os.path.join(CWD, "src", "version_gen.cc")
+
+
+def generate_version_file():
+  tag = subprocess.check_output(
+      "git describe --tags",
+      shell=True,
+      cwd=CWD,
+  ).strip()
+  assert tag
+
+  # Check for commits not exactly matching a tag. Those are candidate builds
+  # for the next version. The output has the form
+  # <tag name>-<n commits>-<hash>.
+  if "-" in tag:
+    version = tag.split("-")[0]
+    candidate = "1"
+  else:
+    version = tag
+    candidate = "0"
+  version_levels = version.split(".")
+
+  # Set default patch level if none is given.
+  if len(version_levels) == 3:
+    version_levels.append("0")
+  assert len(version_levels) == 4
+
+  major, minor, build, patch = version_levels
+
+  # Increment build level for candidate builds.
+  if candidate == "1":
+    build = str(int(build) + 1)
+    patch = "0"
+
+  # Modify version_gen.cc with the new values.
+  output = []
+  with open(VERSION_CC, "r") as f:
+    for line in f:
+      for definition, substitute in (
+          ("MAJOR_VERSION", major),
+          ("MINOR_VERSION", minor),
+          ("BUILD_NUMBER", build),
+          ("PATCH_LEVEL", patch),
+          ("IS_CANDIDATE_VERSION", candidate)):
+        if line.startswith("#define %s" % definition):
+          line =  re.sub("\d+$", substitute, line)
+      output.append(line)
+
+  # Prepare log message.
+  candidate_txt = " (candidate)" if candidate == "1" else ""
+  patch_txt = ".%s" % patch if patch != "0" else ""
+  version_txt = ("%s.%s.%s%s%s" %
+                 (major, minor, build, patch_txt, candidate_txt))
+  log_message = "Modifying version_gen.cc. Set V8 version to %s" %  version_txt
+  return "".join(output), log_message
+
+
+def bypass_version_file():
+  with open(VERSION_CC, "r") as f:
+    return f.read(), "Bypassing V8 version creation."
+
+
+def main():
+  parser = optparse.OptionParser()
+  parser.add_option("--skip",
+                    help="Use raw version.cc file (disables version "
+                         "generation and uses a dummy version).",
+                    default=False, action="store_true")
+  (options, args) = parser.parse_args()
+
+  if options.skip:
+    version_file_content, log_message = bypass_version_file()
+  else:
+    version_file_content, log_message = generate_version_file()
+
+  old_content = ""
+  if os.path.exists(VERSION_GEN_CC):
+    with open(VERSION_GEN_CC, "r") as f:
+      old_content = f.read()
+
+  # Only generate version file if content has changed.
+  if old_content != version_file_content:
+    with open(VERSION_GEN_CC, "w") as f:
+      f.write(version_file_content)
+    # Log what was calculated.
+    print log_message
+
+  return 0
+
+
+if __name__ == "__main__":
+  sys.exit(main())