Enforce rust-check ABI in signatures, calls

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -21,6 +21,7 @@ use rustc_middle::ty::{GenericArgKind, InternalSubsts};
 use rustc_session::parse::feature_err;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
+use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::autoderef::Autoderef;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
@@ -1542,6 +1543,27 @@ fn check_fn_or_method<'tcx>(
         sig.output(),
         hir_decl.output.span(),
     );
+
+    if sig.abi == Abi::RustCall {
+        let span = tcx.def_span(def_id);
+        let has_implicit_self = hir_decl.implicit_self != hir::ImplicitSelfKind::None;
+        let mut inputs = sig.inputs().iter().skip(if has_implicit_self { 1 } else { 0 });
+        // Check that the argument is a tuple
+        if let Some(ty) = inputs.next() {
+            wfcx.register_bound(
+                ObligationCause::new(span, wfcx.body_id, ObligationCauseCode::RustCall),
+                wfcx.param_env,
+                *ty,
+                tcx.require_lang_item(hir::LangItem::Tuple, Some(span)),
+            );
+        } else {
+            tcx.sess.span_err(span, "functions with the \"rust-call\" ABI must take a single non-self argument that is a tuple");
+        }
+        // No more inputs other than the `self` type and the tuple type
+        if inputs.next().is_some() {
+            tcx.sess.span_err(span, "functions with the \"rust-call\" ABI must take a single non-self argument that is a tuple");
+        }
+    }
 }
 
 /// Basically `check_associated_type_bounds`, but separated for now and should be

compiler/rustc_hir_typeck/src/callee.rs

@@ -471,6 +471,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             def_id,
         );
 
+        if fn_sig.abi == abi::Abi::RustCall {
+            let sp = arg_exprs.last().map_or(call_expr.span, |expr| expr.span);
+            if let Some(ty) = fn_sig.inputs().last().copied() {
+                self.register_bound(
+                    ty,
+                    self.tcx.require_lang_item(hir::LangItem::Tuple, Some(sp)),
+                    traits::ObligationCause::new(sp, self.body_id, traits::RustCall),
+                );
+            } else {
+                self.tcx.sess.span_err(
+                        sp,
+                        "functions with the \"rust-call\" ABI must take a single non-self tuple argument",
+                    );
+            }
+        }
+
         fn_sig.output()
     }
 

compiler/rustc_hir_typeck/src/check.rs

@@ -6,13 +6,11 @@ use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::lang_items::LangItem;
-use rustc_hir::{ImplicitSelfKind, ItemKind, Node};
 use rustc_hir_analysis::check::fn_maybe_err;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::infer::RegionVariableOrigin;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::def_id::LocalDefId;
-use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::traits;
 use std::cell::RefCell;
 
@@ -56,41 +54,6 @@ pub(super) fn check_fn<'a, 'tcx>(
 
     fn_maybe_err(tcx, span, fn_sig.abi);
 
-    if fn_sig.abi == Abi::RustCall {
-        let expected_args = if let ImplicitSelfKind::None = decl.implicit_self { 1 } else { 2 };
-
-        let err = || {
-            let item = match tcx.hir().get(fn_id) {
-                Node::Item(hir::Item { kind: ItemKind::Fn(header, ..), .. }) => Some(header),
-                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),
-            };
-
-            if let Some(header) = item {
-                tcx.sess.span_err(header.span, "functions with the \"rust-call\" ABI must take a single non-self argument that is a tuple");
-            }
-        };
-
-        if fn_sig.inputs().len() != expected_args {
-            err()
-        } else {
-            // FIXME(CraftSpider) Add a check on parameter expansion, so we don't just make the ICE happen later on
-            //   This will probably require wide-scale changes to support a TupleKind obligation
-            //   We can't resolve this without knowing the type of the param
-            if !matches!(fn_sig.inputs()[expected_args - 1].kind(), ty::Tuple(_) | ty::Param(_)) {
-                err()
-            }
-        }
-    }
-
     if body.generator_kind.is_some() && can_be_generator.is_some() {
         let yield_ty = fcx
             .next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span });

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -136,6 +136,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             tuple_arguments,
             Some(method.def_id),
         );
+
         method.sig.output()
     }
 

compiler/rustc_hir_typeck/src/lib.rs

@@ -458,7 +458,7 @@ fn report_unexpected_variant_res(tcx: TyCtxt<'_>, res: Res, qpath: &hir::QPath<'
 /// # fn f(x: (isize, isize)) {}
 /// f((1, 2));
 /// ```
-#[derive(Clone, Eq, PartialEq)]
+#[derive(Copy, Clone, Eq, PartialEq)]
 enum TupleArgumentsFlag {
     DontTupleArguments,
     TupleArguments,

compiler/rustc_middle/src/traits/mod.rs

@@ -438,6 +438,8 @@ pub enum ObligationCauseCode<'tcx> {
     },
 
     AscribeUserTypeProvePredicate(Span),
+
+    RustCall,
 }
 
 /// The 'location' at which we try to perform HIR-based wf checking.

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

@@ -2407,7 +2407,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             | ObligationCauseCode::CheckAssociatedTypeBounds { .. }
             | ObligationCauseCode::LetElse
             | ObligationCauseCode::BinOp { .. }
-            | ObligationCauseCode::AscribeUserTypeProvePredicate(..) => {}
+            | ObligationCauseCode::AscribeUserTypeProvePredicate(..)
+            | ObligationCauseCode::RustCall => {}
             ObligationCauseCode::SliceOrArrayElem => {
                 err.note("slice and array elements must have `Sized` type");
             }