Merge pull request #19127 from ChayimFriedman2/different-generic-args

feat: Refactor path lowering and serve a new path diagnostic

crates/ide-diagnostics/src/handlers/parenthesized_generic_args_without_fn_trait.rs

@@ -0,0 +1,59 @@
+use crate::{Diagnostic, DiagnosticCode, DiagnosticsContext};
+
+// Diagnostic: parenthesized-generic-args-without-fn-trait
+//
+// This diagnostic is shown when a `Fn`-trait-style generic parameters (`Trait(A, B) -> C`)
+// was used on non-`Fn` trait/type.
+pub(crate) fn parenthesized_generic_args_without_fn_trait(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::ParenthesizedGenericArgsWithoutFnTrait,
+) -> Diagnostic {
+    Diagnostic::new_with_syntax_node_ptr(
+        ctx,
+        DiagnosticCode::RustcHardError("E0214"),
+        "parenthesized type parameters may only be used with a `Fn` trait",
+        d.args.map(Into::into),
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn fn_traits_work() {
+        check_diagnostics(
+            r#"
+//- minicore: async_fn, fn
+fn foo<
+    A: Fn(),
+    B: FnMut() -> i32,
+    C: FnOnce(&str, bool),
+    D: AsyncFn::(u32) -> u32,
+    E: AsyncFnMut(),
+    F: AsyncFnOnce() -> bool,
+>() {}
+        "#,
+        );
+    }
+
+    #[test]
+    fn non_fn_trait() {
+        check_diagnostics(
+            r#"
+struct Struct<T>(T);
+enum Enum<T> { EnumVariant(T) }
+type TypeAlias<T> = bool;
+
+type Foo = TypeAlias() -> bool;
+                 // ^^ error: parenthesized type parameters may only be used with a `Fn` trait
+
+fn foo(_a: Struct(i32)) {
+              // ^^^^^ error: parenthesized type parameters may only be used with a `Fn` trait
+    let _ = <Enum::(u32)>::EnumVariant(0);
+              // ^^^^^^^ error: parenthesized type parameters may only be used with a `Fn` trait
+}
+        "#,
+        );
+    }
+}

crates/ide-diagnostics/src/lib.rs

@@ -43,6 +43,7 @@ mod handlers {
     pub(crate) mod mutability_errors;
     pub(crate) mod no_such_field;
     pub(crate) mod non_exhaustive_let;
+    pub(crate) mod parenthesized_generic_args_without_fn_trait;
     pub(crate) mod private_assoc_item;
     pub(crate) mod private_field;
     pub(crate) mod remove_trailing_return;
@@ -466,7 +467,12 @@ pub fn semantic_diagnostics(
                 Some(it) => it,
                 None => continue,
             },
-            AnyDiagnostic::GenericArgsProhibited(d) => handlers::generic_args_prohibited::generic_args_prohibited(&ctx, &d)
+            AnyDiagnostic::GenericArgsProhibited(d) => {
+                handlers::generic_args_prohibited::generic_args_prohibited(&ctx, &d)
+            }
+            AnyDiagnostic::ParenthesizedGenericArgsWithoutFnTrait(d) => {
+                handlers::parenthesized_generic_args_without_fn_trait::parenthesized_generic_args_without_fn_trait(&ctx, &d)
+            }
         };
         res.push(d)
     }