Add support for folder-specific settings (#2537)

This PR allows you to customize Zed's settings within a particular
folder by creating a `.zed/settings.json` file within that folder.

Todo

* [x] respect folder-specific settings for local projects
* [x] respect folder-specific settings in remote projects
* [x] pass a path when retrieving editor/language settings
* [x] pass a path when retrieving copilot settings
* [ ] update the `Setting` trait to make it clear which types of
settings are locally overridable

Release Notes:

* Added support for folder-specific settings. You can customize Zed's
settings within a particular folder by creating a `.zed` directory and a
`.zed/settings.json` file within that folder.

crates/project/src/project_tests.rs

@@ -63,6 +63,66 @@ async fn test_symlinks(cx: &mut gpui::TestAppContext) {
     });
 }
 
+#[gpui::test]
+async fn test_managing_project_specific_settings(
+    deterministic: Arc<Deterministic>,
+    cx: &mut gpui::TestAppContext,
+) {
+    init_test(cx);
+
+    let fs = FakeFs::new(cx.background());
+    fs.insert_tree(
+        "/the-root",
+        json!({
+            ".zed": {
+                "settings.json": r#"{ "tab_size": 8 }"#
+            },
+            "a": {
+                "a.rs": "fn a() {\n    A\n}"
+            },
+            "b": {
+                ".zed": {
+                    "settings.json": r#"{ "tab_size": 2 }"#
+                },
+                "b.rs": "fn b() {\n  B\n}"
+            }
+        }),
+    )
+    .await;
+
+    let project = Project::test(fs.clone(), ["/the-root".as_ref()], cx).await;
+    let worktree = project.read_with(cx, |project, cx| project.worktrees(cx).next().unwrap());
+
+    deterministic.run_until_parked();
+    cx.read(|cx| {
+        let tree = worktree.read(cx);
+
+        let settings_a = language_settings(
+            None,
+            Some(
+                &(File::for_entry(
+                    tree.entry_for_path("a/a.rs").unwrap().clone(),
+                    worktree.clone(),
+                ) as _),
+            ),
+            cx,
+        );
+        let settings_b = language_settings(
+            None,
+            Some(
+                &(File::for_entry(
+                    tree.entry_for_path("b/b.rs").unwrap().clone(),
+                    worktree.clone(),
+                ) as _),
+            ),
+            cx,
+        );
+
+        assert_eq!(settings_a.tab_size.get(), 8);
+        assert_eq!(settings_b.tab_size.get(), 2);
+    });
+}
+
 #[gpui::test]
 async fn test_managing_language_servers(
     deterministic: Arc<Deterministic>,