Add a more useful error message in cases when a merge base for ush change cannot be determined.

iclanton · iclanton · commit 122c15c4cf7d · 2022-10-03T12:56:47.000-07:00
diff --git a/common/changes/@microsoft/rush/shallow-clone-error-message_2022-10-03-19-56.json b/common/changes/@microsoft/rush/shallow-clone-error-message_2022-10-03-19-56.json
@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@microsoft/rush",
+      "comment": "Add a more useful error message in cases when a merge base for `rush change` cannot be determined.",
+      "type": "none"
+    }
+  ],
+  "packageName": "@microsoft/rush"
+}
diff --git a/libraries/rush-lib/src/logic/Git.ts b/libraries/rush-lib/src/logic/Git.ts
@@ -230,16 +230,26 @@ export class Git {
     }
 
     const gitPath: string = this.getGitPathOrThrow();
-    const output: string = this._executeGitCommandAndCaptureOutput(gitPath, [
-      '--no-optional-locks',
-      'merge-base',
-      '--',
-      'HEAD',
-      targetBranch
-    ]);
-    const result: string = output.trim();
-
-    return result;
+    try {
+      const output: string = this._executeGitCommandAndCaptureOutput(gitPath, [
+        '--no-optional-locks',
+        'merge-base',
+        '--',
+        'HEAD',
+        targetBranch
+      ]);
+      const result: string = output.trim();
+
+      return result;
+    } catch (e) {
+      terminal.writeErrorLine(
+        `Unable to determine merge base for branch "${targetBranch}". ` +
+          'This can occur if the current clone is a shallow clone. If this clone is running in a CI ' +
+          'pipeline, check your pipeline settings to ensure that the clone depth includes ' +
+          'the expected merge base. If this clone is running locally, consider running "git fetch --deepen".'
+      );
+      throw new AlreadyReportedError();
+    }
   }
 
   public getBlobContent({ blobSpec, repositoryRoot }: IGetBlobOptions): string {
