mach: Do not use unstable rust for rustfmt (#31441)

We can use stable rust if we pass the unstable configuration as
command-line arguments to rustfmt itself. This prevents needing to
install an unstable rust toolchain.

The one downside here is that it doesn't seem that "ignore" is
supported so we have to start formatting the files in "third_party."
This shouldn't be a huge issue because we don't plan to check much more
rust code into those directories.

components/constellation/constellation.rs

@@ -4951,7 +4951,9 @@ where
         // If there is no focus browsing context yet, the initial page has
         // not loaded, so there is nothing to save yet.
         let Some(top_level_browsing_context_id) = self.webviews.focused_webview().map(|(id, _)| id)
-            else { return ReadyToSave::NoTopLevelBrowsingContext };
+        else {
+            return ReadyToSave::NoTopLevelBrowsingContext;
+        };
 
         // If there are pending loads, wait for those to complete.
         if !self.pending_changes.is_empty() {

components/gfx/text/shaping/harfbuzz.rs

@@ -11,9 +11,8 @@ use app_units::Au;
 use euclid::default::Point2D;
 // Eventually we would like the shaper to be pluggable, as many operating systems have their own
 // shapers. For now, however, HarfBuzz is a hard dependency.
-use harfbuzz_sys::hb_blob_t;
 use harfbuzz_sys::{
-    hb_blob_create, hb_bool_t, hb_buffer_add_utf8, hb_buffer_create, hb_buffer_destroy,
+    hb_blob_create, hb_blob_t, hb_bool_t, hb_buffer_add_utf8, hb_buffer_create, hb_buffer_destroy,
     hb_buffer_get_glyph_infos, hb_buffer_get_glyph_positions, hb_buffer_get_length,
     hb_buffer_set_direction, hb_buffer_set_script, hb_buffer_t, hb_codepoint_t,
     hb_face_create_for_tables, hb_face_destroy, hb_face_t, hb_feature_t, hb_font_create,

components/script/dom/bindings/buffer_source.rs

@@ -269,8 +269,10 @@ where
                 buffer.get()
             },
         });
-        let Ok(array) = array as Result<CustomAutoRooterGuard<'_, TypedArray<T, *mut JSObject>>, &mut ()> else{
-             return Err(())
+        let Ok(array) =
+            array as Result<CustomAutoRooterGuard<'_, TypedArray<T, *mut JSObject>>, &mut ()>
+        else {
+            return Err(());
         };
         unsafe {
             let slice = (*array).as_slice();
@@ -305,9 +307,10 @@ where
                 buffer.get()
             },
         });
-        let Ok(mut array) =  array as Result<CustomAutoRooterGuard<'_, TypedArray<T, *mut JSObject>>, &mut ()> else
-        {
-            return Err(())
+        let Ok(mut array) =
+            array as Result<CustomAutoRooterGuard<'_, TypedArray<T, *mut JSObject>>, &mut ()>
+        else {
+            return Err(());
         };
         unsafe {
             let slice = (*array).as_mut_slice();

ports/servoshell/minibrowser.rs

@@ -198,7 +198,9 @@ impl Minibrowser {
                     let rect = egui::Rect::from_min_size(min, size);
                     ui.allocate_space(size);
 
-                    let Some(servo_fbo) = servo_framebuffer_id else { return };
+                    let Some(servo_fbo) = servo_framebuffer_id else {
+                        return;
+                    };
                     ui.painter().add(PaintCallback {
                         rect,
                         callback: Arc::new(CallbackFn::new(move |info, painter| {

python/servo/testing_commands.py

@@ -39,6 +39,15 @@ PROJECT_TOPLEVEL_PATH = os.path.abspath(os.path.join(SCRIPT_PATH, "..", ".."))
 WEB_PLATFORM_TESTS_PATH = os.path.join("tests", "wpt", "tests")
 SERVO_TESTS_PATH = os.path.join("tests", "wpt", "mozilla", "tests")
 
+# Servo depends on several `rustfmt` options that are unstable. These are still
+# supported by stable `rustfmt` if they are passed as these command-line arguments.
+UNSTABLE_RUSTFMT_ARGUMENTS = [
+    "--config", "unstable_features=true",
+    "--config", "binop_separator=Back",
+    "--config", "imports_granularity=Module",
+    "--config", "group_imports=StdExternalCrate",
+]
+
 
 def format_toml_files_with_taplo(check_only: bool = True) -> int:
     taplo = shutil.which("taplo")
@@ -206,12 +215,12 @@ class MachCommands(CommandBase):
     def test_tidy(self, all_files, no_progress):
         tidy_failed = tidy.scan(not all_files, not no_progress)
 
-        call(["rustup", "install", "nightly-2023-03-18"])
-        call(["rustup", "component", "add", "rustfmt", "--toolchain", "nightly-2023-03-18"])
-        rustfmt_failed = call(["cargo", "+nightly-2023-03-18", "fmt", "--", "--check"])
+        print("\r ➤  Checking formatting of rust files...")
+        rustfmt_failed = call(["cargo", "fmt", "--", *UNSTABLE_RUSTFMT_ARGUMENTS, "--check"])
         if rustfmt_failed:
             print("Run `./mach fmt` to fix the formatting")
 
+        print("\r ➤  Checking formatting of toml files...")
         taplo_failed = format_toml_files_with_taplo()
 
         tidy_failed = tidy_failed or rustfmt_failed or taplo_failed
@@ -323,9 +332,7 @@ class MachCommands(CommandBase):
         if result != 0:
             return result
 
-        call(["rustup", "install", "nightly-2023-03-18"])
-        call(["rustup", "component", "add", "rustfmt", "--toolchain", "nightly-2023-03-18"])
-        return call(["cargo", "+nightly-2023-03-18", "fmt"])
+        return call(["cargo", "fmt", "--", *UNSTABLE_RUSTFMT_ARGUMENTS])
 
     @Command('update-wpt',
              description='Update the web platform tests',

rustfmt.toml

@@ -1,6 +1,2 @@
 match_block_trailing_comma = true
-binop_separator = "Back"
 reorder_imports = true
-group_imports = "StdExternalCrate"
-imports_granularity = "Module"
-ignore = ["third_party"]

third_party/blurmac/src/framework.rs

@@ -485,6 +485,8 @@ pub mod cb {
     // CBCentralManagerScanOption...Key
 
     // CBAdvertisementData...Key
-    pub use self::link::CBAdvertisementDataServiceUUIDsKey as ADVERTISEMENTDATASERVICEUUIDSKEY;
-    pub use self::link::CBCentralManagerScanOptionAllowDuplicatesKey as CENTRALMANAGERSCANOPTIONALLOWDUPLICATESKEY;
+    pub use self::link::{
+        CBAdvertisementDataServiceUUIDsKey as ADVERTISEMENTDATASERVICEUUIDSKEY,
+        CBCentralManagerScanOptionAllowDuplicatesKey as CENTRALMANAGERSCANOPTIONALLOWDUPLICATESKEY,
+    };
 }