fix(manager/docker): accept key-only arguments in COPY --from (#31344)

Co-authored-by: Michael Kriese <michael.kriese@visualon.de>

lib/modules/manager/dockerfile/extract.spec.ts

@@ -1,3 +1,4 @@
+import { codeBlock } from 'common-tags';
 import { Fixtures } from '../../../../test/fixtures';
 import type { PackageDependency } from '../types';
 import { extractVariables, getDep } from './extract';
@@ -395,6 +396,31 @@ describe('modules/manager/dockerfile/extract', () => {
       ]);
     });
 
+    it('handles COPY --link --from', () => {
+      const res = extractPackageFile(
+        codeBlock`
+          FROM scratch
+          COPY --link --from=gcr.io/k8s-skaffold/skaffold:v0.11.0 /usr/bin/skaffold /usr/bin/skaffold
+        `,
+        '',
+        {},
+      );
+      expect(res).toEqual({
+        deps: [
+          {
+            autoReplaceStringTemplate:
+              '{{depName}}{{#if newValue}}:{{newValue}}{{/if}}{{#if newDigest}}@{{newDigest}}{{/if}}',
+            currentDigest: undefined,
+            currentValue: 'v0.11.0',
+            datasource: 'docker',
+            depName: 'gcr.io/k8s-skaffold/skaffold',
+            depType: 'final',
+            replaceString: 'gcr.io/k8s-skaffold/skaffold:v0.11.0',
+          },
+        ],
+      });
+    });
+
     it('skips named multistage COPY --from tags', () => {
       const res = extractPackageFile(
         'FROM node:6.12.3 as frontend\n\n# comment\nENV foo=bar\nCOPY --from=frontend /usr/bin/node /usr/bin/node\n',

lib/modules/manager/dockerfile/extract.ts

@@ -385,7 +385,7 @@ export function extractPackageFile(
     const copyFromRegex = new RegExp(
       '^[ \\t]*COPY(?:' +
         escapeChar +
-        '[ \\t]*\\r?\\n| |\\t|#.*?\\r?\\n|--[a-z]+=[a-zA-Z0-9_.:-]+?)+--from=(?<image>\\S+)',
+        '[ \\t]*\\r?\\n| |\\t|#.*?\\r?\\n|--[a-z]+(?:=[a-zA-Z0-9_.:-]+?)?)+--from=(?<image>\\S+)',
       'im',
     ); // TODO #12875 complex for re2 has too many not supported groups
     const copyFromMatch = instruction.match(copyFromRegex);