Add global expression "date"

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

README.md

@@ -612,6 +612,7 @@ attributes are available:
 | `{{branch}}`             | `master`             |
 | `{{tag}}`                | `v1.2.3`             |
 | `{{sha}}`                | `90dd603`            |
+| `{{date 'YYYYMMDD'}}`    | `20210326`           |
 
 ```yaml
 tags: |

__tests__/meta.test.ts

@@ -585,16 +585,18 @@ describe('push', () => {
         images: ['user/app'],
         tags: [
           `type=raw,value=mytag-{{branch}}`,
+          `type=raw,value=mytag-{{date 'YYYYMMDD'}}`,
           `type=raw,value=mytag-{{tag}}`
         ],
       } as Inputs,
       {
         main: 'mytag-master',
-        partial: ['mytag-'],
+        partial: ['mytag-20200110', 'mytag-'],
         latest: false
       } as Version,
       [
         'user/app:mytag-master',
+        'user/app:mytag-20200110',
         'user/app:mytag-'
       ],
       [

dist/index.js

@@ -682,6 +682,7 @@ class Meta {
     }
     setGlobalExp(val) {
         const ctx = this.context;
+        const currentDate = this.date;
         return handlebars.compile(val)({
             branch: function () {
                 if (!/^refs\/heads\//.test(ctx.ref)) {
@@ -697,6 +698,9 @@ class Meta {
             },
             sha: function () {
                 return ctx.sha.substr(0, 7);
+            },
+            date: function (format) {
+                return moment_1.default(currentDate).utc().format(format);
             }
         });
     }

src/meta.ts

@@ -323,6 +323,7 @@ export class Meta {
 
   private setGlobalExp(val): string {
     const ctx = this.context;
+    const currentDate = this.date;
     return handlebars.compile(val)({
       branch: function () {
         if (!/^refs\/heads\//.test(ctx.ref)) {
@@ -338,6 +339,9 @@ export class Meta {
       },
       sha: function () {
         return ctx.sha.substr(0, 7);
+      },
+      date: function (format) {
+        return moment(currentDate).utc().format(format);
       }
     });
   }