From f9bc8b0c9b9a9a56687c5086e372d0be689ebd01 Mon Sep 17 00:00:00 2001
From: Brian McGee <brian@bmcgee.ie>
Date: Thu, 8 Aug 2024 09:52:29 +0100
Subject: [PATCH] fix(git): gracefully handle a file in the index but not in
 the filesystem

This can happen if a user removes a file from the filesystem and that change hasn't been staged yet.

We log a warning when this happens and continue.

Signed-off-by: Brian McGee <brian@bmcgee.ie>
---
 cli/format_test.go | 8 ++++++--
 walk/git.go        | 8 +++++++-
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/cli/format_test.go b/cli/format_test.go
index 1d6d75dd..b8532c38 100644
--- a/cli/format_test.go
+++ b/cli/format_test.go
@@ -530,14 +530,18 @@ func TestGitWorktree(t *testing.T) {
 	as.NoError(err)
 	run(32, 32, 32, 0)
 
-	// remove python directory
+	// remove python directory from the worktree
 	as.NoError(wt.RemoveGlob("python/*"))
 	run(28, 28, 28, 0)
 
+	// remove nixpkgs.toml from the filesystem but leave it in the index
+	as.NoError(os.Remove(filepath.Join(tempDir, "nixpkgs.toml")))
+	run(27, 27, 27, 0)
+
 	// walk with filesystem instead of git
 	_, err = cmd(t, "-c", "--config-file", configPath, "--tree-root", tempDir, "--walk", "filesystem")
 	as.NoError(err)
-	assertStats(t, as, 61, 61, 61, 0)
+	assertStats(t, as, 60, 60, 60, 0)
 }
 
 func TestPathsArg(t *testing.T) {
diff --git a/walk/git.go b/walk/git.go
index 4dc91967..f0c5b52e 100644
--- a/walk/git.go
+++ b/walk/git.go
@@ -13,6 +13,7 @@ import (
 )
 
 type gitWalker struct {
+	log           *log.Logger
 	root          string
 	paths         chan string
 	repo          *git.Repository
@@ -59,7 +60,11 @@ func (g gitWalker) Walk(ctx context.Context, fn WalkFunc) error {
 					path := filepath.Join(g.root, entry.Name)
 
 					info, err := os.Lstat(path)
-					if err != nil {
+					if os.IsNotExist(err) {
+						// the underlying file might have been removed without the change being staged yet
+						g.log.Warnf("Path %s is in the index but appears to have been removed from the filesystem", path)
+						continue
+					} else if err != nil {
 						return fmt.Errorf("failed to stat %s: %w", path, err)
 					}
 
@@ -136,6 +141,7 @@ func NewGit(root string, paths chan string) (Walker, error) {
 		return nil, fmt.Errorf("failed to open git repo: %w", err)
 	}
 	return &gitWalker{
+		log:           log.WithPrefix("walker[git]"),
 		root:          root,
 		paths:         paths,
 		repo:          repo,