Add image output

It is sometimes useful to easily refer to the image built. This adds an
output image which is the full image including a SHA tag.

action.yml

@@ -45,6 +45,11 @@ inputs:
       This flag can be used in case only authentication against docker 
       repo is needed
     default: false
+outputs:
+  builder:
+    description: buildx builder name
+  image:
+    description: full image name including git SHA tag
 runs:
   using: 'node12'
   main: 'dist/index.js'

src/docker.ts

@@ -2,11 +2,14 @@ import {info, debug, warning, startGroup, endGroup} from '@actions/core';
 import {exec} from './exec';
 import {Inputs} from './inputs';
 import * as state from './state';
+import * as outputs from './outputs';
 
 export async function build(inputs: Inputs): Promise<void> {
   startGroup('🏃 Starting build');
 
-  const args = await getBuildArgs(inputs);
+  const shaTag = await getSHATag(inputs.repository);
+  outputs.setImage(shaTag);
+  const args = await getBuildArgs(inputs, shaTag);
   const res = await exec('docker', args, false);
   if (res.stderr !== '' && !res.success) {
     throw new Error(`buildx call failed: ${res.stderr.trim()}`);
@@ -15,7 +18,7 @@ export async function build(inputs: Inputs): Promise<void> {
   endGroup();
 }
 
-async function getBuildArgs(inputs: Inputs): Promise<string[]> {
+async function getBuildArgs(inputs: Inputs, shaTag: string): Promise<string[]> {
   const args = ['buildx', 'build'];
   if (inputs.file) {
     args.push('--file', inputs.file);
@@ -26,7 +29,7 @@ async function getBuildArgs(inputs: Inputs): Promise<string[]> {
   await asyncForEach(inputs.tags, async tag => {
     args.push('--tag', tag);
   });
-  args.push('--tag', await shaTag(inputs.repository));
+  args.push('--tag', shaTag);
   if (inputs.push) {
     args.push('--push');
   }
@@ -52,7 +55,7 @@ export function isDockerhubRepository(repository: string): boolean {
   return registry === '';
 }
 
-async function shaTag(repository: string): Promise<string> {
+async function getSHATag(repository: string): Promise<string> {
   const res = await exec('git', ['rev-parse', 'HEAD'], true);
   if (res.stderr !== '' && !res.success) {
     throw new Error(`git rev-parse HEAD failed: ${res.stderr.trim()}`);

src/outputs.ts

@@ -3,3 +3,7 @@ import {setOutput} from '@actions/core';
 export function setBuilder(name: string): void {
   setOutput('builder', name);
 }
+
+export function setImage(name: string): void {
+  setOutput('image', name);
+}