feat(ng-dev/pr): add dry-run flag to pr merge tooling (#733)

Add a --dry-run flag to allow for checking if a PR is currently mergable into its target branches
in the current state.

PR Close #733

ng-dev/pr/merge/cli.ts

@@ -7,6 +7,7 @@
  */
 
 import {Argv, Arguments, CommandModule} from 'yargs';
+import {addDryRunFlag} from '../../utils/dry-run.js';
 
 import {addGithubTokenOption} from '../../utils/git/github-yargs.js';
 
@@ -18,11 +19,12 @@ export interface MergeCommandOptions {
   pr: number;
   branchPrompt: boolean;
   forceManualBranches: boolean;
+  dryRun: boolean;
 }
 
 /** Builds the command. */
 function builder(argv: Argv) {
-  return addGithubTokenOption(argv)
+  return addDryRunFlag(addGithubTokenOption(argv))
     .help()
     .strict()
     .positional('pr', {
@@ -43,8 +45,13 @@ function builder(argv: Argv) {
 }
 
 /** Handles the command. */
-async function handler({pr, branchPrompt, forceManualBranches}: Arguments<MergeCommandOptions>) {
-  await mergePullRequest(pr, {branchPrompt, forceManualBranches});
+async function handler({
+  pr,
+  branchPrompt,
+  forceManualBranches,
+  dryRun,
+}: Arguments<MergeCommandOptions>) {
+  await mergePullRequest(pr, {branchPrompt, forceManualBranches, dryRun});
 }
 
 /** yargs command module describing the command. */

ng-dev/pr/merge/failures.ts

@@ -13,7 +13,7 @@ export class FatalMergeToolError extends Error {
   }
 }
 
-/** Error class that can be thrown the user aborted the merge manually. */
+/** Error class that can be thrown when the user aborted the merge manually. */
 export class UserAbortedMergeToolError extends Error {}
 
 export class MismatchedTargetBranchFatalError extends FatalMergeToolError {

ng-dev/pr/merge/merge-pull-request.ts

@@ -48,7 +48,6 @@ export async function mergePullRequest(prNumber: number, flags: PullRequestMerge
   ): Promise<boolean> {
     try {
       await tool.merge(prNumber, validationConfig);
-      Log.info(green(`Successfully merged the pull request: #${prNumber}`));
       return true;
     } catch (e) {
       // Catch errors to the Github API for invalid requests. We want to
@@ -63,6 +62,7 @@ export async function mergePullRequest(prNumber: number, flags: PullRequestMerge
         Log.warn('Manually aborted merging..');
         return false;
       }
+
       if (e instanceof FatalMergeToolError) {
         Log.error(`Could not merge the specified pull request. Error:`);
         Log.error(` -> ${bold(e.message)}`);

ng-dev/pr/merge/merge-tool.ts

@@ -7,15 +7,15 @@
  */
 
 import {AuthenticatedGitClient} from '../../utils/git/authenticated-git-client.js';
-import {GitCommandError} from '../../utils/git/git-client.js';
 import semver from 'semver';
 import {prompt} from 'inquirer';
-import {Log, red, yellow} from '../../utils/logging.js';
+import {green, Log, red, yellow} from '../../utils/logging.js';
 
 import {PullRequestConfig} from '../config/index.js';
 import {
   getCaretakerNotePromptMessage,
   getTargetedBranchesConfirmationPromptMessage,
+  getTargetedBranchesMessage,
 } from './messages.js';
 import {loadAndValidatePullRequest, PullRequest} from './pull-request.js';
 import {GithubApiMergeStrategy} from './strategies/api-merge.js';
@@ -34,11 +34,13 @@ import {PullRequestValidationConfig} from '../common/validation/validation-confi
 export interface PullRequestMergeFlags {
   branchPrompt: boolean;
   forceManualBranches: boolean;
+  dryRun: boolean;
 }
 
 const defaultPullRequestMergeFlags: PullRequestMergeFlags = {
   branchPrompt: true,
   forceManualBranches: false,
+  dryRun: false,
 };
 
 /**
@@ -64,7 +66,6 @@ export class MergeTool {
    * @param validationConfig Pull request validation config. Can be modified to skip
    *   certain non-fatal validations.
    */
-
   async merge(prNumber: number, validationConfig: PullRequestValidationConfig): Promise<void> {
     if (this.git.hasUncommittedChanges()) {
       throw new FatalMergeToolError(
@@ -139,6 +140,12 @@ export class MergeTool {
       // Check for conflicts between the pull request and target branches.
       await strategy.check(pullRequest);
 
+      if (this.flags.dryRun) {
+        Log.info(getTargetedBranchesMessage(pullRequest));
+        Log.info(green(`  ✓  Mergeablility of pull request confirmed, exiting dry run.`));
+        return;
+      }
+
       if (
         // In cases where manual branch targeting is used, the user already confirmed.
         !this.flags.forceManualBranches &&
@@ -150,6 +157,7 @@ export class MergeTool {
 
       // Perform the merge and pass-through potential failures.
       await strategy.merge(pullRequest);
+      Log.info(green(`  ✓  Successfully merged the pull request: #${prNumber}`));
     } finally {
       // Switch back to the previous branch. We need to do this before deleting the temporary
       // branches because we cannot delete branches which are currently checked out.

ng-dev/pr/merge/messages.ts

@@ -17,6 +17,10 @@ export function getCaretakerNotePromptMessage(pullRequest: PullRequest): string
 }
 
 export function getTargetedBranchesConfirmationPromptMessage(pullRequest: PullRequest): string {
-  const targetBranchListAsString = pullRequest.targetBranches.map((b) => ` - ${b}\n`).join('');
-  return `Pull request #${pullRequest.prNumber} will merge into:\n${targetBranchListAsString}\nDo you want to proceed merging?`;
+  return `${getTargetedBranchesMessage(pullRequest)}}\nDo you want to proceed merging?`;
+}
+
+export function getTargetedBranchesMessage(pullRequest: PullRequest): string {
+  const targetBranchListAsString = pullRequest.targetBranches.map((b) => ` - ${b}`).join('\n');
+  return `Pull request #${pullRequest.prNumber} will merge into:\n${targetBranchListAsString}`;
 }

ng-dev/pr/merge/pull-request.ts

@@ -18,6 +18,7 @@ import {ActiveReleaseTrains} from '../../release/versioning/active-release-train
 import {PullRequestValidationConfig} from '../common/validation/validation-config.js';
 import {assertValidPullRequest} from '../common/validation/validate-pull-request.js';
 import {TEMP_PR_HEAD_BRANCH} from './strategies/strategy.js';
+import {getRepositoryGitUrl} from '../../utils/git/github-urls.js';
 
 /** Interface that describes a pull request. */
 export interface PullRequest {
@@ -33,8 +34,6 @@ export interface PullRequest {
   targetBranches: string[];
   /** Branch that the PR targets in the Github UI. */
   githubTargetBranch: string;
-  /** List of branches this PR must be cherry picked into. */
-  cherryPickTargetBranches: string[];
   /** Count of commits in this pull request. */
   commitCount: number;
   /** Optional SHA that this pull request needs to be based on. */
@@ -112,6 +111,8 @@ export async function loadAndValidatePullRequest(
     !!config.pullRequest.caretakerNoteLabel &&
     labels.includes(config.pullRequest.caretakerNoteLabel);
 
+  git.runGraceful(['fetch', getRepositoryGitUrl(config.github), `pull/${prNumber}/head`]);
+
   /** Number of commits in the pull request. */
   const commitCount = prData.commits.totalCount;
   /**
@@ -123,7 +124,7 @@ export async function loadAndValidatePullRequest(
    * change. We avoid this issue around this by parsing the base revision so that we are able
    * to reference a specific SHA before a autosquash rebase could be performed.
    */
-  const baseSha = git.run(['rev-parse', `${TEMP_PR_HEAD_BRANCH}~${commitCount}`]).stdout.trim();
+  const baseSha = git.run(['rev-parse', `${prData.headRefOid}~${commitCount}`]).stdout.trim();
   /* Git revision range that matches the pull request commits. */
   const revisionRange = `${baseSha}..${TEMP_PR_HEAD_BRANCH}`;
 
@@ -139,7 +140,6 @@ export async function loadAndValidatePullRequest(
     revisionRange,
     hasCaretakerNote,
     targetBranches: target.branches,
-    cherryPickTargetBranches: target.branches.filter((b) => b !== githubTargetBranch),
     title: prData.title,
   };
 }

ng-dev/pr/merge/strategies/api-merge.ts

@@ -45,9 +45,9 @@ export class GithubApiMergeStrategy extends MergeStrategy {
    * @throws {FatalMergeToolError} A fatal error if the merge could not be performed.
    */
   override async merge(pullRequest: PullRequest): Promise<void> {
-    const {githubTargetBranch, prNumber, needsCommitMessageFixup, cherryPickTargetBranches} =
-      pullRequest;
+    const {githubTargetBranch, prNumber, needsCommitMessageFixup, targetBranches} = pullRequest;
     const method = this._getMergeActionFromPullRequest(pullRequest);
+    const cherryPickTargetBranches = targetBranches.filter((b) => b !== githubTargetBranch);
 
     const mergeOptions: OctokitMergeParams = {
       pull_number: prNumber,