git: Handle buffer file path changes

crates/project/src/git_store.rs

@@ -1335,7 +1335,44 @@ impl GitStore {
                     diffs.remove(buffer_id);
                 }
             }
+            BufferStoreEvent::BufferChangedFilePath { buffer, .. } => {
+                // Whenever a buffer's file path changes, it's possible that the
+                // new path is actually a path that is being tracked by a git
+                // repository. In that case, we'll want to update the buffer's
+                // `BufferDiffState`, in case it already has one.
+                let buffer_id = buffer.read(cx).remote_id();
+                let diff_state = self.diffs.get(&buffer_id);
+                let repo = self.repository_and_path_for_buffer_id(buffer_id, cx);
+
+                if let Some(diff_state) = diff_state
+                    && let Some((repo, repo_path)) = repo
+                {
+                    let buffer = buffer.clone();
+                    let diff_state = diff_state.clone();
+
+                    cx.spawn(async move |_git_store, cx| {
+                        async {
+                            let diff_bases_change = repo
+                                .update(cx, |repo, cx| {
+                                    repo.load_committed_text(buffer_id, repo_path, cx)
+                                })?
+                                .await?;
 
+                            diff_state.update(cx, |diff_state, cx| {
+                                let buffer_snapshot = buffer.read(cx).text_snapshot();
+                                diff_state.diff_bases_changed(
+                                    buffer_snapshot,
+                                    Some(diff_bases_change),
+                                    cx,
+                                );
+                            })
+                        }
+                        .await
+                        .log_err();
+                    })
+                    .detach();
+                }
+            }
             _ => {}
         }
     }

crates/project/src/project_tests.rs

@@ -9611,6 +9611,120 @@ async fn test_repository_deduplication(cx: &mut gpui::TestAppContext) {
     pretty_assertions::assert_eq!(repos, [Path::new(path!("/root/project")).into()]);
 }
 
+#[gpui::test]
+async fn test_buffer_changed_file_path_updates_git_diff(cx: &mut gpui::TestAppContext) {
+    init_test(cx);
+
+    let file_1_committed = String::from(r#"file_1_committed"#);
+    let file_1_staged = String::from(r#"file_1_staged"#);
+    let file_2_committed = String::from(r#"file_2_committed"#);
+    let file_2_staged = String::from(r#"file_2_staged"#);
+    let buffer_contents = String::from(r#"buffer"#);
+
+    let fs = FakeFs::new(cx.background_executor.clone());
+    fs.insert_tree(
+        path!("/dir"),
+        json!({
+            ".git": {},
+           "src": {
+               "file_1.rs": file_1_committed.clone(),
+               "file_2.rs": file_2_committed.clone(),
+           }
+        }),
+    )
+    .await;
+
+    fs.set_head_for_repo(
+        path!("/dir/.git").as_ref(),
+        &[
+            ("src/file_1.rs", file_1_committed.clone()),
+            ("src/file_2.rs", file_2_committed.clone()),
+        ],
+        "deadbeef",
+    );
+    fs.set_index_for_repo(
+        path!("/dir/.git").as_ref(),
+        &[
+            ("src/file_1.rs", file_1_staged.clone()),
+            ("src/file_2.rs", file_2_staged.clone()),
+        ],
+    );
+
+    let project = Project::test(fs.clone(), [path!("/dir").as_ref()], cx).await;
+
+    let buffer = project
+        .update(cx, |project, cx| {
+            project.open_local_buffer(path!("/dir/src/file_1.rs"), cx)
+        })
+        .await
+        .unwrap();
+
+    buffer.update(cx, |buffer, cx| {
+        buffer.edit([(0..buffer.len(), buffer_contents.as_str())], None, cx);
+    });
+
+    let unstaged_diff = project
+        .update(cx, |project, cx| {
+            project.open_unstaged_diff(buffer.clone(), cx)
+        })
+        .await
+        .unwrap();
+
+    cx.run_until_parked();
+
+    unstaged_diff.update(cx, |unstaged_diff, _cx| {
+        let base_text = unstaged_diff.base_text_string().unwrap();
+        assert_eq!(base_text, file_1_staged, "Should start with file_1 staged");
+    });
+
+    // Save the buffer as `file_2.rs`, which should trigger the
+    // `BufferChangedFilePath` event.
+    project
+        .update(cx, |project, cx| {
+            let worktree_id = project.worktrees(cx).next().unwrap().read(cx).id();
+            let path = ProjectPath {
+                worktree_id,
+                path: rel_path("src/file_2.rs").into(),
+            };
+            project.save_buffer_as(buffer.clone(), path, cx)
+        })
+        .await
+        .unwrap();
+
+    cx.run_until_parked();
+
+    // Verify that the diff bases have been updated to file_2's contents due to
+    // the `BufferChangedFilePath` event being handled.
+    unstaged_diff.update(cx, |unstaged_diff, cx| {
+        let snapshot = buffer.read(cx).snapshot();
+        let base_text = unstaged_diff.base_text_string().unwrap();
+        assert_eq!(
+            base_text, file_2_staged,
+            "Diff bases should be automatically updated to file_2 staged content"
+        );
+
+        let hunks: Vec<_> = unstaged_diff.hunks(&snapshot, cx).collect();
+        assert!(!hunks.is_empty(), "Should have diff hunks for file_2");
+    });
+
+    let uncommitted_diff = project
+        .update(cx, |project, cx| {
+            project.open_uncommitted_diff(buffer.clone(), cx)
+        })
+        .await
+        .unwrap();
+
+    cx.run_until_parked();
+
+    uncommitted_diff.update(cx, |uncommitted_diff, _cx| {
+        let base_text = uncommitted_diff.base_text_string().unwrap();
+        assert_eq!(
+            base_text, file_2_committed,
+            "Uncommitted diff should compare against file_2 committed content"
+        );
+    });
+}
+
 async fn search(
     project: &Entity<Project>,
     query: SearchQuery,