Fixes #142.

Adds `date: "git Last Modified"` support to use last git commit as `page.date` variable.

package.json

@@ -98,6 +98,7 @@
     "@sindresorhus/slugify": "^1.1.2",
     "browser-sync": "^2.27.7",
     "chokidar": "^3.5.3",
+    "cross-spawn": "^7.0.3",
     "debug": "^4.3.3",
     "dependency-graph": "^0.11.0",
     "ejs": "^3.1.6",

src/Template.js

@@ -6,11 +6,14 @@ const mkdir = util.promisify(fs.mkdir);
 const os = require("os");
 const path = require("path");
 const normalize = require("normalize-path");
-const isPlainObject = require("./Util/IsPlainObject");
 const lodashGet = require("lodash/get");
 const lodashSet = require("lodash/set");
 const { DateTime } = require("luxon");
 
+const isPlainObject = require("./Util/IsPlainObject");
+const ConsoleLogger = require("./Util/ConsoleLogger");
+const getDateFromGitLastUpdated = require("./Util/DateGitLastUpdated");
+
 const TemplateData = require("./TemplateData");
 const TemplateContent = require("./TemplateContent");
 const TemplatePath = require("./TemplatePath");
@@ -19,7 +22,6 @@ const TemplateLayout = require("./TemplateLayout");
 const TemplateFileSlug = require("./TemplateFileSlug");
 const ComputedData = require("./ComputedData");
 const Pagination = require("./Plugins/Pagination");
-const ConsoleLogger = require("./Util/ConsoleLogger");
 const TemplateBehavior = require("./TemplateBehavior");
 
 const TemplateContentPrematureUseError = require("./Errors/TemplateContentPrematureUseError");
@@ -1016,30 +1018,40 @@ class Template extends TemplateContent {
         // YAML does its own date parsing
         debug("getMappedDate: YAML parsed it: %o", data.date);
         return data.date;
-      } else {
-        // string
-        if (data.date.toLowerCase() === "last modified") {
-          return this._getDateInstance("ctimeMs");
-        } else if (data.date.toLowerCase() === "created") {
-          return this._getDateInstance("birthtimeMs");
-        } else {
-          // try to parse with Luxon
-          let date = DateTime.fromISO(data.date, { zone: "utc" });
-          if (!date.isValid) {
-            throw new Error(
-              `date front matter value (${data.date}) is invalid for ${this.inputPath}`
-            );
-          }
-          debug(
-            "getMappedDate: Luxon parsed %o: %o and %o",
-            data.date,
-            date,
-            date.toJSDate()
-          );
+      }
 
-          return date.toJSDate();
+      // special strings
+      if (data.date.toLowerCase() === "git last modified") {
+        let d = getDateFromGitLastUpdated(this.inputPath);
+        if (d) {
+          return d;
         }
+
+        // return now if this file is not yet available in `git`
+        return Date.now();
+      }
+      if (data.date.toLowerCase() === "last modified") {
+        return this._getDateInstance("ctimeMs");
+      }
+      if (data.date.toLowerCase() === "created") {
+        return this._getDateInstance("birthtimeMs");
+      }
+
+      // try to parse with Luxon
+      let date = DateTime.fromISO(data.date, { zone: "utc" });
+      if (!date.isValid) {
+        throw new Error(
+          `date front matter value (${data.date}) is invalid for ${this.inputPath}`
+        );
       }
+      debug(
+        "getMappedDate: Luxon parsed %o: %o and %o",
+        data.date,
+        date,
+        date.toJSDate()
+      );
+
+      return date.toJSDate();
     } else {
       let filepathRegex = this.inputPath.match(/(\d{4}-\d{2}-\d{2})/);
       if (filepathRegex !== null) {

src/Util/DateGitLastUpdated.js

@@ -0,0 +1,28 @@
+const spawn = require("cross-spawn");
+
+/* Thank you to Vuepress!
+ * https://github.com/vuejs/vuepress/blob/89440ce552675859189ed4ab254ce19c4bba5447/packages/%40vuepress/plugin-last-updated/index.js
+ * MIT licensed: https://github.com/vuejs/vuepress/blob/89440ce552675859189ed4ab254ce19c4bba5447/LICENSE
+ */
+function getGitLastUpdatedTimeStamp(filePath) {
+  return (
+    parseInt(
+      spawn
+        .sync(
+          "git",
+          // Formats https://www.git-scm.com/docs/git-log#_pretty_formats
+          // %at author date, UNIX timestamp
+          ["log", "-1", "--format=%at", filePath]
+        )
+        .stdout.toString("utf-8")
+    ) * 1000
+  );
+}
+
+// return a Date
+module.exports = function (inputPath) {
+  let timestamp = getGitLastUpdatedTimeStamp(inputPath);
+  if (timestamp) {
+    return new Date(timestamp);
+  }
+};

test/EleventyTest.js

@@ -2,6 +2,7 @@ const test = require("ava");
 const Eleventy = require("../src/Eleventy");
 const EleventyWatchTargets = require("../src/EleventyWatchTargets");
 const TemplateConfig = require("../src/TemplateConfig");
+const DateGitLastUpdated = require("../src/Util/DateGitLastUpdated");
 
 test("Eleventy, defaults inherit from config", async (t) => {
   let elev = new Eleventy();
@@ -412,3 +413,14 @@ test("Unicode in front matter `tags`, issue #670", async (t) => {
 
   t.is(results[0].content.trim(), "2,all,Cañon City,");
 });
+
+test("#142: date 'git Last Modified' populates page.date", async (t) => {
+  let elev = new Eleventy("./test/stubs-142/", "./test/stubs-142/_site");
+
+  let results = await elev.toJSON();
+  let [result] = results;
+
+  // This doesn’t test the validity of the function, only that it populates page.date.
+  let comparisonDate = DateGitLastUpdated("./test/stubs-142/index.njk");
+  t.is(result.content.trim(), "" + comparisonDate.getTime());
+});

test/stubs-142/index.njk

@@ -1,4 +1,4 @@
 ---
 date: git Last Modified
 ---
-{{ page.date }}
+{{ page.date.getTime() }}