ci: Fix changed files detection for forks

.buildkite/ci.mjs

@@ -14,6 +14,7 @@ import {
   getCommitMessage,
   getLastSuccessfulBuild,
   getMainBranch,
+  getRepositoryOwner,
   getTargetBranch,
   isBuildkite,
   isFork,
@@ -370,7 +371,7 @@ async function main() {
   }
 
   console.log("Checking changed files...");
-  const baseRef = getCommit();
+  const baseRef = isFork() ? `${getRepositoryOwner()}:${getCommit()}` : getCommit();
   console.log(" - Base Ref:", baseRef);
   const headRef = lastBuild?.commit_id || getTargetBranch() || getMainBranch();
   console.log(" - Head Ref:", headRef);

scripts/utils.mjs

@@ -376,6 +376,20 @@ export function getRepository(cwd) {
   }
 }
 
+/**
+ * @param {string} [cwd]
+ * @returns {string | undefined}
+ */
+export function getRepositoryOwner(cwd) {
+  const repository = getRepository(cwd);
+  if (repository) {
+    const [owner] = repository.split("/");
+    if (owner) {
+      return owner;
+    }
+  }
+}
+
 /**
  * @param {string} [cwd]
  * @returns {string | undefined}