feat(ng-dev): introduce an option to disable fixup commits in commit validation (#2541)

Some repositories do not allow fixup commits. This feature adds a configuration option to disallow such commits during the validation process.

Author: alan-agius4

ng-dev/commit-message/validate.spec.ts

@@ -266,6 +266,33 @@ describe('validate-commit-message.js', () => {
           );
         });
       });
+
+      describe('with `disallowFixup`', () => {
+        it('when true should fail', async () => {
+          const msg = 'fixup! foo';
+
+          expectValidationResult(
+            await validateCommitMessage(msg, {
+              disallowFixup: true,
+              nonFixupCommitHeaders: ['foo', 'bar', 'baz'],
+            }),
+            INVALID,
+            ['The commit must be manually fixed-up into the target commit as fixup commits are disallowed'],
+          );
+        });
+
+        it('when false should pass', async () => {
+          const msg = 'fixup! foo';
+
+          expectValidationResult(
+            await validateCommitMessage(msg, {
+              disallowFixup: false,
+              nonFixupCommitHeaders: ['foo', 'bar', 'baz'],
+            }),
+            VALID,
+          );
+        });
+      });
     });
 
     describe('minBodyLength', () => {

ng-dev/commit-message/validate.ts

@@ -15,6 +15,7 @@ import {Commit, parseCommitMessage} from './parse.js';
 /** Options for commit message validation. */
 export interface ValidateCommitMessageOptions {
   disallowSquash?: boolean;
+  disallowFixup?: boolean;
   nonFixupCommitHeaders?: string[];
 }
 
@@ -90,6 +91,14 @@ export async function validateCommitMessage(
     // stripping the `fixup! ` prefix), otherwise we assume this verification will happen in another
     // check.
     if (commit.isFixup) {
+      if (options.disallowFixup) {
+        errors.push(
+          'The commit must be manually fixed-up into the target commit as fixup commits are disallowed',
+        );
+
+        return false;
+      }
+
       if (options.nonFixupCommitHeaders && !options.nonFixupCommitHeaders.includes(commit.header)) {
         errors.push(
           'Unable to find match for fixup commit among prior commits: ' +