fix: Add more useful error for non-ignored symlinks

Author: s0

src/git.ts

@@ -7,6 +7,16 @@ import {
   CommitFilesResult,
 } from "./interface";
 
+/**
+ * @see https://isomorphic-git.org/docs/en/walk#walkerentry-mode
+ */
+const FILE_MODES = {
+  directory: 0o40000,
+  file: 0o100644,
+  executableFile: 0o100755,
+  symlink: 0o120000,
+} as const;
+
 export const commitChangesFromRepo = async ({
   base,
   repoDirectory = process.cwd(),
@@ -50,6 +60,14 @@ export const commitChangesFromRepo = async ({
       ) {
         return null;
       }
+      if (
+        (await commit?.mode()) === FILE_MODES.symlink ||
+        (await workdir?.mode()) === FILE_MODES.symlink
+      ) {
+        throw new Error(
+          `Unexpected symlink at ${filepath}, GitHub API only supports files and directories. You may need to add this file to .gitignore`,
+        );
+      }
       const prevOid = await commit?.oid();
       const currentOid = await workdir?.oid();
       // Don't include files that haven't changed, and exist in both trees