build: allow overriding electron version (#39974)

script/get-git-version.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+
+import subprocess
+import os
+
+# Find the nearest tag to the current HEAD.
+# This is equivalent to our old logic of "use a value in package.json" for the
+# following reasons:
+#
+# 1. Whenever we updated the package.json we ALSO pushed a tag with the same
+#    version.
+# 2. Whenever we _reverted_ a bump all we actually did was push a commit that
+#    deleted the tag and changed the version number back.
+#
+# The only difference in the "git describe" technique is that technically a
+# commit can "change" its version number if a tag is created / removed
+# retroactively.  i.e. the first time a commit is pushed it will be 1.2.3
+# and after the tag is made rebuilding the same commit will result in it being
+# 1.2.4.
+
+try:
+  output = subprocess.check_output(
+      ['git', 'describe', '--tags', '--abbrev=0'],
+      cwd=os.path.abspath(os.path.join(os.path.dirname(__file__), '..')),
+      stderr=subprocess.PIPE,
+      universal_newlines=True)
+  version = output.strip().replace('v', '')
+  print(version)
+except Exception:
+  # When there is error we print a null version string instead of throwing an
+  # exception, this is because for linux/bsd packages and some vendor builds
+  # electron is built from a source code tarball and there is no git information
+  # there.
+  print('0.0.0-no-git-tag-found')