Auto merge of #108138 - compiler-errors:malformed-fn-trait, r=TaKO8Ki

Move `Fn*` traits malformedness protections to typeck

I found it strange that we were doing a custom well-formedness check just for the `Fn*` traits' `call_*` fn items. My understanding from the git history is that this is just to avoid ICEs later on in typeck.

Well, that well-formedness check isn't even implemented correctly for `FnOnce::call_once`, or `FnMut::call_mut` for that matter. Instead, this PR just makes the typeck checks more robust, and leaves it up to the call-site to report errors when lang items are implemented in funny ways.

This coincidentally fixes another ICE where a the `Add` lang item is implemented with a `add` item that's a const instead of a method.

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -16,7 +16,7 @@ use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::trait_def::TraitSpecializationKind;
 use rustc_middle::ty::{
-    self, ir::TypeVisitor, AdtKind, DefIdTree, GenericParamDefKind, Ty, TyCtxt, TypeFoldable,
+    self, ir::TypeVisitor, AdtKind, GenericParamDefKind, Ty, TyCtxt, TypeFoldable,
     TypeSuperVisitable,
 };
 use rustc_middle::ty::{GenericArgKind, InternalSubsts};
@@ -277,56 +277,6 @@ fn check_trait_item(tcx: TyCtxt<'_>, trait_item: &hir::TraitItem<'_>) {
     };
     check_object_unsafe_self_trait_by_name(tcx, trait_item);
     check_associated_item(tcx, def_id, span, method_sig);
-
-    let encl_trait_def_id = tcx.local_parent(def_id);
-    let encl_trait = tcx.hir().expect_item(encl_trait_def_id);
-    let encl_trait_def_id = encl_trait.owner_id.to_def_id();
-    let fn_lang_item_name = if Some(encl_trait_def_id) == tcx.lang_items().fn_trait() {
-        Some("fn")
-    } else if Some(encl_trait_def_id) == tcx.lang_items().fn_mut_trait() {
-        Some("fn_mut")
-    } else {
-        None
-    };
-
-    if let (Some(fn_lang_item_name), "call") =
-        (fn_lang_item_name, trait_item.ident.name.to_ident_string().as_str())
-    {
-        // We are looking at the `call` function of the `fn` or `fn_mut` lang item.
-        // Do some rudimentary sanity checking to avoid an ICE later (issue #83471).
-        if let Some(hir::FnSig { decl, span, .. }) = method_sig {
-            if let [self_ty, _] = decl.inputs {
-                if !matches!(self_ty.kind, hir::TyKind::Ref(_, _)) {
-                    tcx.sess
-                        .struct_span_err(
-                            self_ty.span,
-                            &format!(
-                                "first argument of `call` in `{fn_lang_item_name}` lang item must be a reference",
-                            ),
-                        )
-                        .emit();
-                }
-            } else {
-                tcx.sess
-                    .struct_span_err(
-                        *span,
-                        &format!(
-                            "`call` function in `{fn_lang_item_name}` lang item takes exactly two arguments",
-                        ),
-                    )
-                    .emit();
-            }
-        } else {
-            tcx.sess
-                .struct_span_err(
-                    trait_item.span,
-                    &format!(
-                        "`call` trait item in `{fn_lang_item_name}` lang item must be a function",
-                    ),
-                )
-                .emit();
-        }
-    }
 }
 
 /// Require that the user writes where clauses on GATs for the implicit

compiler/rustc_hir_typeck/src/callee.rs

@@ -247,6 +247,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 adjusted_ty,
                 opt_input_type.as_ref().map(slice::from_ref),
             ) {
+                // Check for `self` receiver on the method, otherwise we can't use this as a `Fn*` trait.
+                if !self.tcx.associated_item(ok.value.def_id).fn_has_self_parameter {
+                    self.tcx.sess.delay_span_bug(
+                        call_expr.span,
+                        "input to overloaded call fn is not a self receiver",
+                    );
+                    return None;
+                }
+
                 let method = self.register_infer_ok_obligations(ok);
                 let mut autoref = None;
                 if borrow {
@@ -257,7 +266,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         // caused an error elsewhere.
                         self.tcx
                             .sess
-                            .delay_span_bug(call_expr.span, "input to call/call_mut is not a ref?");
+                            .delay_span_bug(call_expr.span, "input to call/call_mut is not a ref");
                         return None;
                     };
 
@@ -271,6 +280,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         target: method.sig.inputs()[0],
                     });
                 }
+
                 return Some((autoref, method));
             }
         }
@@ -823,7 +833,7 @@ impl<'a, 'tcx> DeferredCallResolution<'tcx> {
                 );
                 err.help(
                     "make sure the `fn`/`fn_mut`/`fn_once` lang items are defined \
-                     and have associated `call`/`call_mut`/`call_once` functions",
+                     and have correctly defined `call`/`call_mut`/`call_once` methods",
                 );
                 err.emit();
             }

compiler/rustc_hir_typeck/src/method/mod.rs

@@ -380,6 +380,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             );
             return None;
         };
+
+        if method_item.kind != ty::AssocKind::Fn {
+            self.tcx.sess.delay_span_bug(tcx.def_span(method_item.def_id), "not a method");
+            return None;
+        }
+
         let def_id = method_item.def_id;
         let generics = tcx.generics_of(def_id);
 

tests/ui/lang-items/bad-add-impl.rs

@@ -0,0 +1,18 @@
+#![feature(no_core)]
+#![feature(lang_items)]
+#![no_core]
+
+#[lang = "sized"]
+trait Sized {}
+
+#[lang = "add"]
+trait Add<T> {
+    const add: u32 = 1u32;
+}
+
+impl Add<u32> for u32 {}
+
+fn main() {
+    1u32 + 1u32;
+    //~^ ERROR cannot add `u32` to `u32`
+}

tests/ui/lang-items/bad-add-impl.stderr

@@ -0,0 +1,11 @@
+error[E0369]: cannot add `u32` to `u32`
+  --> $DIR/bad-add-impl.rs:16:10
+   |
+LL |     1u32 + 1u32;
+   |     ---- ^ ---- u32
+   |     |
+   |     u32
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0369`.

tests/ui/lang-items/fn-fn_mut-call-ill-formed.bad_item.stderr

@@ -0,0 +1,18 @@
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:39:5
+   |
+LL |     a();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:43:5
+   |
+LL |     b();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: aborting due to 2 previous errors
+

tests/ui/lang-items/fn-fn_mut-call-ill-formed.bad_sig.stderr

@@ -0,0 +1,18 @@
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:39:5
+   |
+LL |     a();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:43:5
+   |
+LL |     b();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: aborting due to 2 previous errors
+

tests/ui/lang-items/fn-fn_mut-call-ill-formed.fn_bad_item.stderr

@@ -0,0 +1,18 @@
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:42:5
+   |
+LL |     a();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:47:5
+   |
+LL |     b();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: aborting due to 2 previous errors
+

tests/ui/lang-items/fn-fn_mut-call-ill-formed.fn_bad_sig.stderr

@@ -0,0 +1,18 @@
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:42:5
+   |
+LL |     a();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:47:5
+   |
+LL |     b();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: aborting due to 2 previous errors
+

tests/ui/lang-items/fn-fn_mut-call-ill-formed.fn_mut_bad_item.stderr

@@ -0,0 +1,18 @@
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:42:5
+   |
+LL |     a();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:47:5
+   |
+LL |     b();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: aborting due to 2 previous errors
+

tests/ui/lang-items/fn-fn_mut-call-ill-formed.fn_mut_bad_sig.stderr

@@ -0,0 +1,18 @@
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:42:5
+   |
+LL |     a();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:47:5
+   |
+LL |     b();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: aborting due to 2 previous errors
+

tests/ui/lang-items/fn-fn_mut-call-ill-formed.fn_once_bad_item.stderr

@@ -0,0 +1,18 @@
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:42:5
+   |
+LL |     a();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:47:5
+   |
+LL |     b();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: aborting due to 2 previous errors
+

tests/ui/lang-items/fn-fn_mut-call-ill-formed.fn_once_bad_sig.stderr

@@ -0,0 +1,18 @@
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:42:5
+   |
+LL |     a();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: failed to find an overloaded call trait for closure call
+  --> $DIR/fn-fn_mut-call-ill-formed.rs:47:5
+   |
+LL |     b();
+   |     ^^^
+   |
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
+
+error: aborting due to 2 previous errors
+

tests/ui/lang-items/fn-fn_mut-call-ill-formed.rs

@@ -1,27 +1,49 @@
-// Make sure that an error is reported if the `call` function of the
+// revisions: fn_once_bad_item fn_once_bad_sig fn_mut_bad_item fn_mut_bad_sig fn_bad_item fn_bad_sig
-// `fn`/`fn_mut` lang item is grossly ill-formed.
 
 #![feature(lang_items)]
 #![feature(no_core)]
 #![no_core]
 
+#[lang = "sized"]
+trait Sized {}
+
+#[cfg(any(fn_bad_item, fn_bad_sig))]
 #[lang = "fn"]
 trait MyFn<T> {
+    #[cfg(fn_bad_sig)]
+    fn call(i: i32) -> i32 { 0 }
+
+    #[cfg(fn_bad_item)]
     const call: i32 = 42;
-    //~^ ERROR: `call` trait item in `fn` lang item must be a function
 }
 
+#[cfg(any(fn_mut_bad_item, fn_mut_bad_sig))]
 #[lang = "fn_mut"]
 trait MyFnMut<T> {
-    fn call(i: i32, j: i32) -> i32 { i + j }
+    #[cfg(fn_mut_bad_sig)]
-    //~^ ERROR: first argument of `call` in `fn_mut` lang item must be a reference
+    fn call_mut(i: i32) -> i32 { 0 }
+
+    #[cfg(fn_mut_bad_item)]
+    const call_mut: i32 = 42;
+}
+
+#[cfg(any(fn_once_bad_item, fn_once_bad_sig))]
+#[lang = "fn_once"]
+trait MyFnOnce<T> {
+    #[cfg(fn_once_bad_sig)]
+    fn call_once(i: i32) -> i32 { 0 }
+
+    #[cfg(fn_once_bad_item)]
+    const call_once: i32 = 42;
 }
 
 fn main() {
     let a = || 42;
     a();
+    //~^ ERROR failed to find an overloaded call trait for closure call
 
     let mut i = 0;
-    let mut b = || { i += 1; };
+    let mut b = || { };
     b();
+    //~^ ERROR failed to find an overloaded call trait for closure call
 }

tests/ui/lang-items/fn-fn_mut-call-ill-formed.stderr

@@ -1,14 +0,0 @@
-error: `call` trait item in `fn` lang item must be a function
-  --> $DIR/fn-fn_mut-call-ill-formed.rs:10:5
-   |
-LL |     const call: i32 = 42;
-   |     ^^^^^^^^^^^^^^^^^^^^^
-
-error: first argument of `call` in `fn_mut` lang item must be a reference
-  --> $DIR/fn-fn_mut-call-ill-formed.rs:16:16
-   |
-LL |     fn call(i: i32, j: i32) -> i32 { i + j }
-   |                ^^^
-
-error: aborting due to 2 previous errors
-

tests/ui/lang-items/issue-86238.stderr

@@ -4,7 +4,7 @@ error: failed to find an overloaded call trait for closure call
 LL |     one()
    |     ^^^^^
    |
-   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have associated `call`/`call_mut`/`call_once` functions
+   = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods
 
 error: aborting due to previous error