Warn when permissions not set for PR comment

src/job-summary.ts

@@ -1,6 +1,7 @@
 import * as core from '@actions/core'
 import * as github from '@actions/github'
 import {SUMMARY_ENV_VAR} from '@actions/core/lib/summary'
+import {RequestError} from '@octokit/request-error'
 
 import * as params from './input-params'
 import {BuildResult} from './build-results'
@@ -30,9 +31,6 @@ export async function generateJobSummary(buildResults: BuildResult[], cacheListe
 }
 
 async function addPRComment(jobSummary: string): Promise<void> {
-    try {
-        const github_token = params.getGithubToken()
-
     const context = github.context
     if (context.payload.pull_request == null) {
         core.info('No pull_request trigger: not adding PR comment')
@@ -47,16 +45,33 @@ async function addPRComment(jobSummary: string): Promise<void> {
 
 ${jobSummary}`
 
+    const github_token = params.getGithubToken()
     const octokit = github.getOctokit(github_token)
+    try {
         await octokit.rest.issues.createComment({
             ...context.repo,
             issue_number: pull_request_number,
             body: prComment
         })
     } catch (error) {
-        core.warning(`Failed to generate PR comment: ${String(error)}`)
+        if (error instanceof RequestError) {
+            core.warning(buildWarningMessage(error))
+        } else {
+            throw error
         }
     }
+}
+
+function buildWarningMessage(error: RequestError): string {
+    const mainWarning = `Failed to generate PR comment.\n${String(error)}`
+    if (error.message === 'Resource not accessible by integration') {
+        return `${mainWarning}
+Please ensure that the 'pull-requests: write' permission is available for the workflow job.
+Note that this permission is never available for a workflow triggered from a repository fork.
+        `
+    }
+    return mainWarning
+}
 
 function renderSummaryTable(results: BuildResult[]): string {
     if (results.length === 0) {