Rollup merge of #79675 - CraftSpider:79669, r=estebank

Make sure rust-call errors occur correctly for traits

Fixes #79669

Adds trait method resolution to the error, and adds UI tests to ensure it doesn't happen again. Opening as draft because I'm getting weird link errors from unrelated code on my machine, and want to see what CI thinks.

Author: JohnTitor

compiler/rustc_typeck/src/check/check.rs

@@ -103,6 +103,10 @@ pub(super) fn check_fn<'a, 'tcx>(
                 Node::ImplItem(hir::ImplItem {
                     kind: hir::ImplItemKind::Fn(header, ..), ..
                 }) => Some(header),
+                Node::TraitItem(hir::TraitItem {
+                    kind: hir::TraitItemKind::Fn(header, ..),
+                    ..
+                }) => Some(header),
                 // Closures are RustCall, but they tuple their arguments, so shouldn't be checked
                 Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => None,
                 node => bug!("Item being checked wasn't a function/closure: {:?}", node),

src/test/ui/abi/issues/issue-22565-rust-call.rs

@@ -3,6 +3,30 @@
 extern "rust-call" fn b(_i: i32) {}
 //~^ ERROR A function with the "rust-call" ABI must take a single non-self argument that is a tuple
 
+trait Tr {
+    extern "rust-call" fn a();
+
+    extern "rust-call" fn b() {}
+    //~^ ERROR A function with the "rust-call" ABI must take a single non-self argument
+}
+
+struct Foo;
+
+impl Foo {
+    extern "rust-call" fn bar() {}
+    //~^ ERROR A function with the "rust-call" ABI must take a single non-self argument
+}
+
+impl Tr for Foo {
+    extern "rust-call" fn a() {}
+    //~^ ERROR A function with the "rust-call" ABI must take a single non-self argument
+}
+
 fn main () {
     b(10);
+
+    Foo::bar();
+
+    <Foo as Tr>::a();
+    <Foo as Tr>::b();
 }

src/test/ui/abi/issues/issue-22565-rust-call.stderr

@@ -4,5 +4,23 @@ error: A function with the "rust-call" ABI must take a single non-self argument
 LL | extern "rust-call" fn b(_i: i32) {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to previous error
+error: A function with the "rust-call" ABI must take a single non-self argument that is a tuple
+  --> $DIR/issue-22565-rust-call.rs:9:5
+   |
+LL |     extern "rust-call" fn b() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: A function with the "rust-call" ABI must take a single non-self argument that is a tuple
+  --> $DIR/issue-22565-rust-call.rs:16:5
+   |
+LL |     extern "rust-call" fn bar() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: A function with the "rust-call" ABI must take a single non-self argument that is a tuple
+  --> $DIR/issue-22565-rust-call.rs:21:5
+   |
+LL |     extern "rust-call" fn a() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 4 previous errors