Improve closure support

bevy_lint/src/lints/borrowed_reborrowable.rs

@@ -12,7 +12,13 @@
 //!
 //! # Known Issues
 //!
-//! This lint does not currently support closures.
+//! This lint does not currently support the `Fn` traits or function pointers.
+//! 
+//! This means the following types will not be caught by the lint:
+//! 
+//! - `impl FnOnce(&mut Commands)`
+//! - `Box<dyn FnMut(&mut Commands)>`
+//! - `fn(&mut Commands)`
 //!
 //! # Example
 //!
@@ -75,14 +81,12 @@ impl<'tcx> LateLintPass<'tcx> for BorrowedReborrowable {
         _: Span,
         def_id: LocalDefId,
     ) {
-        // Closures are not currently supported, as `tcx.fn_sig()` crashes for them.
-        if let FnKind::Closure = kind {
-            return;
-        }
-
         // We use `instantiate_identity` to discharge the binder since we don't
         // mind using placeholders for any bound arguments
-        let fn_sig = cx.tcx.fn_sig(def_id).instantiate_identity();
+        let fn_sig = match kind {
+            FnKind::Closure => cx.tcx.closure_user_provided_sig(def_id).value,
+            _ => cx.tcx.fn_sig(def_id).instantiate_identity(),
+        };
 
         let arg_names = cx.tcx.fn_arg_names(def_id);
 

bevy_lint/tests/ui/borrowed_reborrowable/bug_174.rs

@@ -0,0 +1,26 @@
+//! This test tracks the bug reported in [#174]. When this starts failing, the bug has been fixed.
+//!
+//! [#174]: https://github.com/TheBevyFlock/bevy_cli/issues/174
+
+//@check-pass
+
+#![feature(register_tool)]
+#![register_tool(bevy)]
+#![deny(bevy::borrowed_reborrowable)]
+
+use bevy::prelude::*;
+
+fn main() {
+    let mut world = World::new();
+
+    closure_wrapper(world.commands(), |commands| commands.spawn_empty().id());
+    closure_wrapper2(world.commands(), |commands| commands.spawn_empty().id());
+}
+
+fn closure_wrapper(mut commands: Commands, f: impl FnOnce(&mut Commands) -> Entity) {
+    f(&mut commands);
+}
+
+fn closure_wrapper2(mut commands: Commands, f: fn(&mut Commands) -> Entity) {
+    f(&mut commands);
+}

bevy_lint/tests/ui/borrowed_reborrowable/closures.rs

@@ -0,0 +1,20 @@
+//! This tests the `borrowed_reborrowable` lint, specifically when triggered on closure types.
+
+#![feature(register_tool)]
+#![register_tool(bevy)]
+#![deny(bevy::borrowed_reborrowable)]
+
+use bevy::prelude::*;
+
+fn main() {
+    let mut world = World::new();
+    let mut commands = world.commands();
+
+    //~| HELP: use `Commands` instead
+    //~v ERROR: parameter takes `&mut Commands` instead of a re-borrowed `Commands`
+    let closure = |commands: &mut Commands| {
+        commands.spawn_empty();
+    };
+
+    closure(&mut commands);
+}

bevy_lint/tests/ui/borrowed_reborrowable/closures.stderr

@@ -0,0 +1,14 @@
+error: parameter takes `&mut Commands` instead of a re-borrowed `Commands`
+  --> tests/ui/borrowed_reborrowable/closures.rs:15:20
+   |
+15 |     let closure = |commands: &mut Commands| {
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^ help: use `Commands` instead: `mut commands: bevy::prelude::Commands<'_, '_>`
+   |
+note: the lint level is defined here
+  --> tests/ui/borrowed_reborrowable/closures.rs:5:9
+   |
+5  | #![deny(bevy::borrowed_reborrowable)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+