feat: improve warning message

src/commitSha.ts

@@ -469,9 +469,28 @@ export const getSHAForPullRequestEvent = async (
     core.error(
       `Similar commit hashes detected: previous sha: ${previousSha} is equivalent to the current sha: ${currentSha}.`
     )
-    core.error(
-      `Please verify that both commits are valid, and increase the fetch_depth to a number higher than ${inputs.fetchDepth}.`
-    )
+    // This occurs if a PR is created from a forked repository and the event is pull_request_target.
+    //  - name: Checkout to branch
+    //    uses: actions/checkout@v3
+    // Without setting the repository to use the same repository as the pull request will cause the previousSha
+    // to be the same as the currentSha since the currentSha cannot be found in the local history.
+    // The solution is to use:
+    //   - name: Checkout to branch
+    //     uses: actions/checkout@v3
+    //     with:
+    //       repository: ${{ github.event.pull_request.head.repo.full_name }}
+    if (env.GITHUB_EVENT_NAME === 'pull_request_target') {
+      core.warning(
+        'If this pull request is from a forked repository, please set the checkout action `repository` input to the same repository as the pull request.'
+      )
+      core.warning(
+        'This can be done by setting actions/checkout `repository` to ${{ github.event.pull_request.head.repo.full_name }}'
+      )
+    } else {
+      core.error(
+        `Please verify that both commits are valid, and increase the fetch_depth to a number higher than ${inputs.fetchDepth}.`
+      )
+    }
     throw new Error('Similar commit hashes detected.')
   }
 

src/env.ts

@@ -15,6 +15,7 @@ export type Env = {
   GITHUB_EVENT_PULL_REQUEST_NUMBER: string
   GITHUB_EVENT_PULL_REQUEST_BASE_SHA: string
   GITHUB_EVENT_PULL_REQUEST_HEAD_SHA: string
+  GITHUB_EVENT_NAME: string
 }
 
 type GithubEvent = {
@@ -66,6 +67,7 @@ export const getEnv = async (): Promise<Env> => {
     GITHUB_EVENT_FORCED: eventJson.forced || '',
     GITHUB_REF_NAME: process.env.GITHUB_REF_NAME || '',
     GITHUB_REF: process.env.GITHUB_REF || '',
-    GITHUB_WORKSPACE: process.env.GITHUB_WORKSPACE || ''
+    GITHUB_WORKSPACE: process.env.GITHUB_WORKSPACE || '',
+    GITHUB_EVENT_NAME: process.env.GITHUB_EVENT_NAME || ''
   }
 }