From 70301370f932f37415a4e8acee862789a2c89b35 Mon Sep 17 00:00:00 2001
From: Daniel Rozenberg <rodaniel@ampproject.org>
Date: Mon, 9 Jul 2018 15:25:27 -0400
Subject: [PATCH] Generate a consistent version number when building/disting

---
 build-system/exec.js             |  1 -
 build-system/git.js              | 19 ++++++++++++++++++
 build-system/internal-version.js | 33 ++++++++++++++++++++++++++++----
 3 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/build-system/exec.js b/build-system/exec.js
index c900570b69c7..873218f538e9 100644
--- a/build-system/exec.js
+++ b/build-system/exec.js
@@ -73,7 +73,6 @@ exports.execOrDie = function(cmd, options) {
 
 /**
  * Executes the provided command, returning the process object.
- * This will throw an exception if something goes wrong.
  * @param {string} cmd
  * @return {!Object}
  */
diff --git a/build-system/git.js b/build-system/git.js
index bdb5e525b1a1..7aca74d1a173 100644
--- a/build-system/git.js
+++ b/build-system/git.js
@@ -83,3 +83,22 @@ exports.gitBranchName = function() {
 exports.gitCommitterEmail = function() {
   return getStdout('git log -1 --pretty=format:"%ae"').trim();
 };
+
+/**
+ * Returns the timestamp of the latest commit on the local branch.
+ * @return {int}
+ */
+exports.gitCommitFormattedTime = function() {
+  return getStdout(
+      'TZ=UTC git log -1 --pretty="%cd" --date=format-local:%y%m%d%H%M%S')
+      .trim();
+};
+
+/**
+ * Returns machine parsable list of uncommitted changed files, or an empty
+ * string if no files were changed.
+ * @return {string}
+ */
+exports.gitStatusPorcelain = function() {
+  return getStdout('git status --porcelain').trim();
+};
diff --git a/build-system/internal-version.js b/build-system/internal-version.js
index 518676ccb02d..789626fe26a0 100644
--- a/build-system/internal-version.js
+++ b/build-system/internal-version.js
@@ -16,8 +16,33 @@
 'use strict';
 
 const argv = require('minimist')(process.argv.slice(2));
+const {gitCommitFormattedTime, gitStatusPorcelain} = require('./git');
 
-// Used to e.g. references the ads binary from the runtime to get
-// version lock.
-exports.VERSION = argv.version ?
-  String(argv.version) : String(Date.now());
+function getVersion() {
+  if (argv.version) {
+    return String(argv.version);
+  } else {
+    // Generate a consistent version number by using the commit* time of the
+    // latest commit on the active branch as the twelve digits, and use the
+    // state of the working directory as the last digit: 0 for a "clean" tree, 1
+    // if there are uncommited changes in the working directory.
+    //
+    // e.g., the version number of a clean (no uncommited changes) tree that was
+    // commited on August 1, 2018 at 14:31:11 EDT would be `1808011831110`
+    // (notice that due to timezone shift, the hour value changes from EDT's 14
+    // to UTC's 18. The last digit denotes that this is a clean tree.)
+    //
+    // *Commit time is different from author time! Commit time is the time that
+    // the PR was merged into master; author time is when the author ran the
+    // "git commit" command.
+    const lastCommitFormattedTime = gitCommitFormattedTime();
+    if (gitStatusPorcelain()) {
+      return `${lastCommitFormattedTime}1`;
+    } else {
+      return `${lastCommitFormattedTime}0`;
+    }
+  }
+}
+
+// Used to e.g. references the ads binary from the runtime to get version lock.
+exports.VERSION = getVersion();