Auto merge of #128792 - compiler-errors:foreign-sig, r=spastorino

Use `FnSig` instead of raw `FnDecl` for `ForeignItemKind::Fn`, fix ICE for `Fn` trait error on safe foreign fn

Let's use `hir::FnSig` instead of `hir::FnDecl + hir::Safety` for `ForeignItemKind::Fn`. This consolidates some handling code between normal fns and foreign fns.

Separetly, fix an ICE where we weren't handling `Fn` trait errors for safe foreign fns.

If perf is bad for the first commit, I can rework the ICE fix to not rely on it. But if perf is good, I prefer we fix and clean up things all at once 👍

r? spastorino

Fixes #128764

compiler/rustc_ast_lowering/src/delegation.rs

@@ -189,7 +189,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     ) -> hir::FnSig<'hir> {
         let header = if let Some(local_sig_id) = sig_id.as_local() {
             match self.resolver.delegation_fn_sigs.get(&local_sig_id) {
-                Some(sig) => self.lower_fn_header(sig.header),
+                Some(sig) => self.lower_fn_header(sig.header, hir::Safety::Safe),
                 None => self.generate_header_error(),
             }
         } else {

compiler/rustc_ast_lowering/src/item.rs

@@ -237,7 +237,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         });
                     let sig = hir::FnSig {
                         decl,
-                        header: this.lower_fn_header(*header),
+                        header: this.lower_fn_header(*header, hir::Safety::Safe),
                         span: this.lower_span(*fn_sig_span),
                     };
                     hir::ItemKind::Fn(sig, generics, body_id)
@@ -668,7 +668,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 ForeignItemKind::Fn(box Fn { sig, generics, .. }) => {
                     let fdec = &sig.decl;
                     let itctx = ImplTraitContext::Universal;
-                    let (generics, (fn_dec, fn_args)) =
+                    let (generics, (decl, fn_args)) =
                         self.lower_generics(generics, Const::No, false, i.id, itctx, |this| {
                             (
                                 // Disallow `impl Trait` in foreign items.
@@ -682,9 +682,15 @@ impl<'hir> LoweringContext<'_, 'hir> {
                                 this.lower_fn_params_to_names(fdec),
                             )
                         });
-                    let safety = self.lower_safety(sig.header.safety, hir::Safety::Unsafe);
 
-                    hir::ForeignItemKind::Fn(fn_dec, fn_args, generics, safety)
+                    // Unmarked safety in unsafe block defaults to unsafe.
+                    let header = self.lower_fn_header(sig.header, hir::Safety::Unsafe);
+
+                    hir::ForeignItemKind::Fn(
+                        hir::FnSig { header, decl, span: self.lower_span(sig.span) },
+                        fn_args,
+                        generics,
+                    )
                 }
                 ForeignItemKind::Static(box StaticItem { ty, mutability, expr: _, safety }) => {
                     let ty = self
@@ -1390,7 +1396,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         coroutine_kind: Option<CoroutineKind>,
         parent_constness: Const,
     ) -> (&'hir hir::Generics<'hir>, hir::FnSig<'hir>) {
-        let header = self.lower_fn_header(sig.header);
+        let header = self.lower_fn_header(sig.header, hir::Safety::Safe);
         // Don't pass along the user-provided constness of trait associated functions; we don't want to
         // synthesize a host effect param for them. We reject `const` on them during AST validation.
         let constness =
@@ -1403,14 +1409,18 @@ impl<'hir> LoweringContext<'_, 'hir> {
         (generics, hir::FnSig { header, decl, span: self.lower_span(sig.span) })
     }
 
-    pub(super) fn lower_fn_header(&mut self, h: FnHeader) -> hir::FnHeader {
+    pub(super) fn lower_fn_header(
+        &mut self,
+        h: FnHeader,
+        default_safety: hir::Safety,
+    ) -> hir::FnHeader {
         let asyncness = if let Some(CoroutineKind::Async { span, .. }) = h.coroutine_kind {
             hir::IsAsync::Async(span)
         } else {
             hir::IsAsync::NotAsync
         };
         hir::FnHeader {
-            safety: self.lower_safety(h.safety, hir::Safety::Safe),
+            safety: self.lower_safety(h.safety, default_safety),
             asyncness: asyncness,
             constness: self.lower_constness(h.constness),
             abi: self.lower_extern(h.ext),

compiler/rustc_hir/src/hir.rs

@@ -3586,7 +3586,7 @@ impl ForeignItem<'_> {
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub enum ForeignItemKind<'hir> {
     /// A foreign function.
-    Fn(&'hir FnDecl<'hir>, &'hir [Ident], &'hir Generics<'hir>, Safety),
+    Fn(FnSig<'hir>, &'hir [Ident], &'hir Generics<'hir>),
     /// A foreign static item (`static ext: u8`).
     Static(&'hir Ty<'hir>, Mutability, Safety),
     /// A foreign type.
@@ -3645,7 +3645,10 @@ impl<'hir> OwnerNode<'hir> {
         match self {
             OwnerNode::TraitItem(TraitItem { kind: TraitItemKind::Fn(fn_sig, _), .. })
             | OwnerNode::ImplItem(ImplItem { kind: ImplItemKind::Fn(fn_sig, _), .. })
-            | OwnerNode::Item(Item { kind: ItemKind::Fn(fn_sig, _, _), .. }) => Some(fn_sig),
+            | OwnerNode::Item(Item { kind: ItemKind::Fn(fn_sig, _, _), .. })
+            | OwnerNode::ForeignItem(ForeignItem {
+                kind: ForeignItemKind::Fn(fn_sig, _, _), ..
+            }) => Some(fn_sig),
             _ => None,
         }
     }
@@ -3654,11 +3657,10 @@ impl<'hir> OwnerNode<'hir> {
         match self {
             OwnerNode::TraitItem(TraitItem { kind: TraitItemKind::Fn(fn_sig, _), .. })
             | OwnerNode::ImplItem(ImplItem { kind: ImplItemKind::Fn(fn_sig, _), .. })
-            | OwnerNode::Item(Item { kind: ItemKind::Fn(fn_sig, _, _), .. }) => Some(fn_sig.decl),
-            OwnerNode::ForeignItem(ForeignItem {
-                kind: ForeignItemKind::Fn(fn_decl, _, _, _),
-                ..
-            }) => Some(fn_decl),
+            | OwnerNode::Item(Item { kind: ItemKind::Fn(fn_sig, _, _), .. })
+            | OwnerNode::ForeignItem(ForeignItem {
+                kind: ForeignItemKind::Fn(fn_sig, _, _), ..
+            }) => Some(fn_sig.decl),
             _ => None,
         }
     }
@@ -3846,11 +3848,13 @@ impl<'hir> Node<'hir> {
         match self {
             Node::TraitItem(TraitItem { kind: TraitItemKind::Fn(fn_sig, _), .. })
             | Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(fn_sig, _), .. })
-            | Node::Item(Item { kind: ItemKind::Fn(fn_sig, _, _), .. }) => Some(fn_sig.decl),
-            Node::Expr(Expr { kind: ExprKind::Closure(Closure { fn_decl, .. }), .. })
-            | Node::ForeignItem(ForeignItem {
-                kind: ForeignItemKind::Fn(fn_decl, _, _, _), ..
-            }) => Some(fn_decl),
+            | Node::Item(Item { kind: ItemKind::Fn(fn_sig, _, _), .. })
+            | Node::ForeignItem(ForeignItem { kind: ForeignItemKind::Fn(fn_sig, _, _), .. }) => {
+                Some(fn_sig.decl)
+            }
+            Node::Expr(Expr { kind: ExprKind::Closure(Closure { fn_decl, .. }), .. }) => {
+                Some(fn_decl)
+            }
             _ => None,
         }
     }
@@ -3874,7 +3878,10 @@ impl<'hir> Node<'hir> {
         match self {
             Node::TraitItem(TraitItem { kind: TraitItemKind::Fn(fn_sig, _), .. })
             | Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(fn_sig, _), .. })
-            | Node::Item(Item { kind: ItemKind::Fn(fn_sig, _, _), .. }) => Some(fn_sig),
+            | Node::Item(Item { kind: ItemKind::Fn(fn_sig, _, _), .. })
+            | Node::ForeignItem(ForeignItem { kind: ForeignItemKind::Fn(fn_sig, _, _), .. }) => {
+                Some(fn_sig)
+            }
             _ => None,
         }
     }
@@ -3949,7 +3956,7 @@ impl<'hir> Node<'hir> {
     pub fn generics(self) -> Option<&'hir Generics<'hir>> {
         match self {
             Node::ForeignItem(ForeignItem {
-                kind: ForeignItemKind::Fn(_, _, generics, _), ..
+                kind: ForeignItemKind::Fn(_, _, generics), ..
             })
             | Node::TraitItem(TraitItem { generics, .. })
             | Node::ImplItem(ImplItem { generics, .. }) => Some(generics),
@@ -4039,8 +4046,8 @@ mod size_asserts {
     static_assert_size!(Expr<'_>, 64);
     static_assert_size!(ExprKind<'_>, 48);
     static_assert_size!(FnDecl<'_>, 40);
-    static_assert_size!(ForeignItem<'_>, 72);
-    static_assert_size!(ForeignItemKind<'_>, 40);
+    static_assert_size!(ForeignItem<'_>, 88);
+    static_assert_size!(ForeignItemKind<'_>, 56);
     static_assert_size!(GenericArg<'_>, 16);
     static_assert_size!(GenericBound<'_>, 48);
     static_assert_size!(Generics<'_>, 56);

compiler/rustc_hir/src/intravisit.rs

@@ -611,9 +611,9 @@ pub fn walk_foreign_item<'v, V: Visitor<'v>>(
     try_visit!(visitor.visit_ident(foreign_item.ident));
 
     match foreign_item.kind {
-        ForeignItemKind::Fn(ref function_declaration, param_names, ref generics, _) => {
+        ForeignItemKind::Fn(ref sig, param_names, ref generics) => {
             try_visit!(visitor.visit_generics(generics));
-            try_visit!(visitor.visit_fn_decl(function_declaration));
+            try_visit!(visitor.visit_fn_decl(sig.decl));
             walk_list!(visitor, visit_ident, param_names.iter().copied());
         }
         ForeignItemKind::Static(ref typ, _, _) => {

compiler/rustc_hir_analysis/src/check/check.rs

@@ -804,8 +804,8 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 
                         let item = tcx.hir().foreign_item(item.id);
                         match &item.kind {
-                            hir::ForeignItemKind::Fn(fn_decl, _, _, _) => {
-                                require_c_abi_if_c_variadic(tcx, fn_decl, abi, item.span);
+                            hir::ForeignItemKind::Fn(sig, _, _) => {
+                                require_c_abi_if_c_variadic(tcx, sig.decl, abi, item.span);
                             }
                             hir::ForeignItemKind::Static(..) => {
                                 check_static_inhabited(tcx, def_id);

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -30,7 +30,7 @@ fn equate_intrinsic_type<'tcx>(
     let (generics, span) = match tcx.hir_node_by_def_id(def_id) {
         hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, generics, _), .. })
         | hir::Node::ForeignItem(hir::ForeignItem {
-            kind: hir::ForeignItemKind::Fn(.., generics, _),
+            kind: hir::ForeignItemKind::Fn(_, _, generics),
             ..
         }) => (tcx.generics_of(def_id), generics.span),
         _ => {

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -350,8 +350,8 @@ fn check_foreign_item<'tcx>(
     );
 
     match item.kind {
-        hir::ForeignItemKind::Fn(decl, ..) => {
-            check_item_fn(tcx, def_id, item.ident, item.span, decl)
+        hir::ForeignItemKind::Fn(sig, ..) => {
+            check_item_fn(tcx, def_id, item.ident, item.span, sig.decl)
         }
         hir::ForeignItemKind::Static(ty, ..) => {
             check_item_type(tcx, def_id, ty.span, UnsizedHandling::AllowIfForeignTail)

compiler/rustc_hir_analysis/src/collect.rs

@@ -1440,11 +1440,9 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_, ty::PolyFn
             icx.lowerer().lower_fn_ty(hir_id, header.safety, header.abi, decl, Some(generics), None)
         }
 
-        ForeignItem(&hir::ForeignItem {
-            kind: ForeignItemKind::Fn(fn_decl, _, _, safety), ..
-        }) => {
+        ForeignItem(&hir::ForeignItem { kind: ForeignItemKind::Fn(sig, _, _), .. }) => {
             let abi = tcx.hir().get_foreign_abi(hir_id);
-            compute_sig_of_foreign_fn_decl(tcx, def_id, fn_decl, abi, safety)
+            compute_sig_of_foreign_fn_decl(tcx, def_id, sig.decl, abi, sig.header.safety)
         }
 
         Ctor(data) | Variant(hir::Variant { data, .. }) if data.ctor().is_some() => {

compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs

@@ -604,7 +604,7 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
 
     fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
         match item.kind {
-            hir::ForeignItemKind::Fn(_, _, generics, _) => {
+            hir::ForeignItemKind::Fn(_, _, generics) => {
                 self.visit_early_late(item.hir_id(), generics, |this| {
                     intravisit::walk_foreign_item(this, item);
                 })

compiler/rustc_hir_pretty/src/lib.rs

@@ -352,16 +352,11 @@ impl<'a> State<'a> {
         self.maybe_print_comment(item.span.lo());
         self.print_outer_attributes(self.attrs(item.hir_id()));
         match item.kind {
-            hir::ForeignItemKind::Fn(decl, arg_names, generics, safety) => {
+            hir::ForeignItemKind::Fn(sig, arg_names, generics) => {
                 self.head("");
                 self.print_fn(
-                    decl,
-                    hir::FnHeader {
-                        safety,
-                        constness: hir::Constness::NotConst,
-                        abi: Abi::Rust,
-                        asyncness: hir::IsAsync::NotAsync,
-                    },
+                    sig.decl,
+                    sig.header,
                     Some(item.ident.name),
                     generics,
                     arg_names,

compiler/rustc_lint/src/types.rs

@@ -1734,13 +1734,16 @@ impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
 
         match it.kind {
-            hir::ForeignItemKind::Fn(decl, _, _, _) if !vis.is_internal_abi(abi) => {
-                vis.check_foreign_fn(it.owner_id.def_id, decl);
+            hir::ForeignItemKind::Fn(sig, _, _) => {
+                if vis.is_internal_abi(abi) {
+                    vis.check_fn(it.owner_id.def_id, sig.decl)
+                } else {
+                    vis.check_foreign_fn(it.owner_id.def_id, sig.decl);
+                }
             }
             hir::ForeignItemKind::Static(ty, _, _) if !vis.is_internal_abi(abi) => {
                 vis.check_foreign_static(it.owner_id, ty.span);
             }
-            hir::ForeignItemKind::Fn(decl, _, _, _) => vis.check_fn(it.owner_id.def_id, decl),
             hir::ForeignItemKind::Static(..) | hir::ForeignItemKind::Type => (),
         }
     }

compiler/rustc_middle/src/hir/map/mod.rs

@@ -816,6 +816,11 @@ impl<'hir> Map<'hir> {
             })
             | Node::ImplItem(ImplItem {
                 kind: ImplItemKind::Fn(sig, ..), span: outer_span, ..
+            })
+            | Node::ForeignItem(ForeignItem {
+                kind: ForeignItemKind::Fn(sig, ..),
+                span: outer_span,
+                ..
             }) => {
                 // Ensure that the returned span has the item's SyntaxContext, and not the
                 // SyntaxContext of the visibility.
@@ -874,10 +879,7 @@ impl<'hir> Map<'hir> {
             },
             Node::Variant(variant) => named_span(variant.span, variant.ident, None),
             Node::ImplItem(item) => named_span(item.span, item.ident, Some(item.generics)),
-            Node::ForeignItem(item) => match item.kind {
-                ForeignItemKind::Fn(decl, _, _, _) => until_within(item.span, decl.output.span()),
-                _ => named_span(item.span, item.ident, None),
-            },
+            Node::ForeignItem(item) => named_span(item.span, item.ident, None),
             Node::Ctor(_) => return self.span(self.tcx.parent_hir_id(hir_id)),
             Node::Expr(Expr {
                 kind: ExprKind::Closure(Closure { fn_decl_span, .. }),

compiler/rustc_middle/src/hir/mod.rs

@@ -202,7 +202,7 @@ pub fn provide(providers: &mut Providers) {
             ..
         })
         | Node::ForeignItem(&ForeignItem {
-            kind: ForeignItemKind::Fn(_, idents, _, _),
+            kind: ForeignItemKind::Fn(_, idents, _),
             ..
         }) = tcx.hir_node(tcx.local_def_id_to_hir_id(def_id))
         {

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

@@ -2729,6 +2729,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
             | Node::TraitItem(&hir::TraitItem {
                 kind: hir::TraitItemKind::Fn(ref sig, _), ..
+            })
+            | Node::ForeignItem(&hir::ForeignItem {
+                kind: hir::ForeignItemKind::Fn(ref sig, _, _),
+                ..
             }) => (
                 sig.span,
                 None,

src/librustdoc/clean/mod.rs

@@ -3094,16 +3094,10 @@ fn clean_maybe_renamed_foreign_item<'tcx>(
     let def_id = item.owner_id.to_def_id();
     cx.with_param_env(def_id, |cx| {
         let kind = match item.kind {
-            hir::ForeignItemKind::Fn(decl, names, generics, safety) => {
-                let (generics, decl) = enter_impl_trait(cx, |cx| {
-                    // NOTE: generics must be cleaned before args
-                    let generics = clean_generics(generics, cx);
-                    let args = clean_args_from_types_and_names(cx, decl.inputs, names);
-                    let decl = clean_fn_decl_with_args(cx, decl, None, args);
-                    (generics, decl)
-                });
-                ForeignFunctionItem(Box::new(Function { decl, generics }), safety)
-            }
+            hir::ForeignItemKind::Fn(sig, names, generics) => ForeignFunctionItem(
+                clean_function(cx, &sig, generics, FunctionArgs::Names(names)),
+                sig.header.safety,
+            ),
             hir::ForeignItemKind::Static(ty, mutability, safety) => ForeignStaticItem(
                 Static { type_: Box::new(clean_ty(ty, cx)), mutability, expr: None },
                 safety,

tests/ui/extern/extern-main-issue-86110.stderr

@@ -2,7 +2,7 @@ error: the `main` function cannot be declared in an `extern` block
   --> $DIR/extern-main-issue-86110.rs:4:5
    |
 LL |     fn main();
-   |     ^^^^^^^^^
+   |     ^^^^^^^^^^
 
 error: aborting due to 1 previous error
 

tests/ui/foreign/foreign-safe-fn-arg-mismatch.rs

@@ -0,0 +1,13 @@
+// Make sure we don't ICE when a foreign fn doesn't implement `Fn` due to arg mismatch.
+
+unsafe extern "Rust" {
+    pub safe fn foo();
+    pub safe fn bar(x: u32);
+}
+
+fn test(_: impl Fn(i32)) {}
+
+fn main() {
+    test(foo); //~ ERROR function is expected to take 1 argument, but it takes 0 arguments
+    test(bar); //~ ERROR type mismatch in function arguments
+}