feat(ng-dev): support exceptional minor target labeling in the interim

Until we have implemented the actual exceptional minor mechanism in both
the release and merge tool, we want to be able to turn `target: minor`
into `target: rc` (internally) so that minor changes can go into the
RC/FF phase that we "misuse" as the exceptional minor release train.

ng-dev/pr/common/targeting/labels.ts

@@ -29,6 +29,7 @@ import {
 import {assertActiveLtsBranch} from './lts-branch.js';
 import {GithubClient} from '../../../utils/git/github.js';
 import {Log} from '../../../utils/logging.js';
+import {assertValidPullRequestConfig, PullRequestConfig} from '../../config/index.js';
 
 /**
  * Gets a list of target labels which should be considered by the merge
@@ -45,9 +46,14 @@ import {Log} from '../../../utils/logging.js';
 export async function getTargetLabelsForActiveReleaseTrains(
   {latest, releaseCandidate, next}: ActiveReleaseTrains,
   api: GithubClient,
-  config: NgDevConfig<{github?: GithubConfig; release?: ReleaseConfig}>,
+  config: NgDevConfig<{
+    github: GithubConfig;
+    pullRequest: PullRequestConfig;
+    release?: ReleaseConfig;
+  }>,
 ): Promise<TargetLabel[]> {
   assertValidGithubConfig(config);
+  assertValidPullRequestConfig(config);
 
   const nextBranchName = getNextBranchName(config.github);
   const repo: ReleaseRepoWithApi = {
@@ -80,7 +86,14 @@ export async function getTargetLabelsForActiveReleaseTrains(
       // TODO: Consider handling this automatically by checking if the NPM version matches
       // the last-minor. If not, then an exceptional minor might be in progress. See:
       // https://docs.google.com/document/d/197kVillDwx-RZtSVOBtPb4BBIAw0E9RT3q3v6DZkykU/edit#heading=h.h7o5pjq6yqd0
-      branches: () => [nextBranchName],
+      branches: () => {
+        // TODO(devversion): Remove this when we actually support exceptional minors.
+        if (config.pullRequest.__specialTreatRcAsExceptionalMinor && releaseCandidate !== null) {
+          return [releaseCandidate.branchName];
+        }
+
+        return [nextBranchName];
+      },
     },
     {
       name: TargetLabelName.PATCH,

ng-dev/pr/config/index.ts

@@ -51,6 +51,14 @@ export interface PullRequestConfig {
    * scopes in patch branches, no breaking changes in minor or patch changes.
    */
   targetLabelExemptScopes?: string[];
+
+  /**
+   * Special flag that should **NOT** be used without confirming with the dev-infra team.
+   * This flag turns the RC/FF release-train into an exceptional minor release-train by:
+   *
+   *    - changing `target: minor` to point to `target: rc` (without the RC merge restrictions)
+   */
+  __specialTreatRcAsExceptionalMinor?: boolean;
 }
 
 /** Loads and validates the merge configuration. */

ng-dev/pr/merge/integration.spec.ts

@@ -115,6 +115,11 @@ describe('default target labels', () => {
     const targetLabels = await getTargetLabelsForActiveReleaseTrains(releaseTrains, api, {
       github: githubConfig,
       release: releaseConfig,
+      pullRequest: {
+        commitMessageFixupLabel: 'commit message fixup',
+        githubApiMerge: false,
+        mergeReadyLabel: 'merge ready',
+      },
       __isNgDevConfigObject: true,
     });
     let label: TargetLabel;