From 0ef1648a3c1f9125290ca188c035e8e42cc485fe Mon Sep 17 00:00:00 2001
From: "Anaz S. Aji" <aji.anaz@gmail.com>
Date: Thu, 11 Jun 2026 15:49:43 +0700
Subject: [PATCH] fix: friendly error when not in a git repo

Detect common git errors (not a git repo, unknown option cached)
and return CoraError::NotInGitRepo instead of raw git stderr.

Before: 'git command diff --cached failed: error: unknown option cached'
After:  'not inside a git repository'

506 tests pass, clippy clean.
---
 src/git/diff.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/git/diff.rs b/src/git/diff.rs
index af90e61c..4678ec0b 100644
--- a/src/git/diff.rs
+++ b/src/git/diff.rs
@@ -58,6 +58,16 @@ fn git_cmd(args: &[&str]) -> std::result::Result<String, CoraError> {
 
     if !output.status.success() {
         let stderr = String::from_utf8_lossy(&output.stderr);
+        let stderr_str = stderr.trim();
+
+        // Detect common git errors and provide friendly messages
+        if stderr_str.contains("not a git repository")
+            || stderr_str.contains("unknown option `cached'")
+            || stderr_str.contains("Not a git repository")
+        {
+            return Err(CoraError::NotInGitRepo);
+        }
+
         return Err(CoraError::GitCommand {
             command: args.join(" "),
             stderr: stderr.to_string(),