From 02bb3aecf37203886251233b843c70ddee628df6 Mon Sep 17 00:00:00 2001
From: Martin von Zweigbergk <martinvonz@google.com>
Date: Mon, 12 Jun 2023 13:31:44 -0700
Subject: [PATCH] tree: don't read file contents on contents/executable
 "conflict"

If one side changes the contents and one side changes the executable
bit, we get a non-trivial conflict in the `TreeValue`s, but once we've
split them up into `FileId`s and bools, we can trivially resolve them
separately, without having to read file contents.
---
 lib/src/tree.rs | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/lib/src/tree.rs b/lib/src/tree.rs
index 5de239178..0329fd4ee 100644
--- a/lib/src/tree.rs
+++ b/lib/src/tree.rs
@@ -680,11 +680,19 @@ fn try_resolve_file_conflict(
     }
     let executable = if let Some(executable) = trivial_merge(&executable_removes, &executable_adds)
     {
-        executable
+        *executable
     } else {
         // We're unable to determine whether the result should be executable
         return Ok(None);
     };
+    if let Some(resolved_file_id) = trivial_merge(&removed_file_ids, &added_file_ids) {
+        // Don't bother reading the file contents if the conflict can be trivially
+        // resolved.
+        return Ok(Some(TreeValue::File {
+            id: resolved_file_id.clone(),
+            executable,
+        }));
+    }
     let mut removed_contents = vec![];
     let mut added_contents = vec![];
     for file_id in removed_file_ids {
@@ -716,10 +724,7 @@ fn try_resolve_file_conflict(
     match merge_result {
         MergeResult::Resolved(merged_content) => {
             let id = store.write_file(filename, &mut merged_content.as_slice())?;
-            Ok(Some(TreeValue::File {
-                id,
-                executable: *executable,
-            }))
+            Ok(Some(TreeValue::File { id, executable }))
         }
         MergeResult::Conflict(_) => Ok(None),
     }