Remove setup-git-user in favor of setting fallback only when identity is missing (#688)

* Experiment with skipping setup-git-user more often

* drop setup-git-user

* fix tests

src/github.ts

@@ -93,10 +93,35 @@ export class GitHub {
     };
   }
 
-  async setupUser() {
-    if (this.commitMode === "github-api") {
+  async ensureGitUser() {
+    // Check the exact identities that Git would use for commits without
+    // allowing Git to fall back to auto-detected values like user@hostname.
+    // This covers explicit GIT_AUTHOR_* / GIT_COMMITTER_* env vars, local
+    // config, and global config. A partial identity, with only a name or only
+    // an email, does not pass this check. If either identity is missing,
+    // configure our default bot user as a fallback.
+    const authorIdentity = await getExecOutput(
+      "git",
+      ["-c", "user.useConfigOnly=true", "var", "GIT_AUTHOR_IDENT"],
+      {
+        cwd: this.cwd,
+        ignoreReturnCode: true,
+        silent: true,
+      },
+    );
+    const committerIdentity = await getExecOutput(
+      "git",
+      ["-c", "user.useConfigOnly=true", "var", "GIT_COMMITTER_IDENT"],
+      {
+        cwd: this.cwd,
+        ignoreReturnCode: true,
+        silent: true,
+      },
+    );
+    if (authorIdentity.exitCode === 0 && committerIdentity.exitCode === 0) {
       return;
     }
+    core.info("Setting Git user to github-actions[bot]");
     await exec("git", ["config", "user.name", `"github-actions[bot]"`], {
       cwd: this.cwd,
     });
@@ -159,6 +184,7 @@ export class GitHub {
       return;
     }
     if (!(await checkIfClean({ cwd: this.cwd }))) {
+      await this.ensureGitUser();
       await commitAll(message, { cwd: this.cwd });
     }
     await push(branch, {