Add Callable trait

Author: oli-obk

compiler/rustc_error_codes/src/error_codes/E0183.md

@@ -31,6 +31,8 @@ impl FnOnce<()> for MyClosure {  // ok!
         println!("{}", self.foo);
     }
 }
+
+impl std::ops::Callable<()> for MyClosure {}
 ```
 
 The arguments must be a tuple representing the argument list.

compiler/rustc_hir/src/lang_items.rs

@@ -207,6 +207,7 @@ language_item_table! {
     Fn,                      kw::Fn,                   fn_trait,                   Target::Trait,          GenericRequirement::Exact(1);
     FnMut,                   sym::fn_mut,              fn_mut_trait,               Target::Trait,          GenericRequirement::Exact(1);
     FnOnce,                  sym::fn_once,             fn_once_trait,              Target::Trait,          GenericRequirement::Exact(1);
+    Callable,                sym::callable,            callable_trait,             Target::Trait,          GenericRequirement::Exact(1);
 
     FnOnceOutput,            sym::fn_once_output,      fn_once_output,             Target::AssocTy,        GenericRequirement::None;
 

compiler/rustc_hir_typeck/src/callee.rs

@@ -3,12 +3,14 @@ use super::method::MethodCallee;
 use super::{Expectation, FnCtxt, TupleArgumentsFlag};
 
 use crate::type_error_struct;
+use hir::LangItem;
 use rustc_ast::util::parser::PREC_POSTFIX;
 use rustc_errors::{struct_span_err, Applicability, Diagnostic, ErrorGuaranteed, StashKey};
 use rustc_hir as hir;
 use rustc_hir::def::{self, CtorKind, Namespace, Res};
 use rustc_hir::def_id::DefId;
 use rustc_hir_analysis::autoderef::Autoderef;
+use rustc_infer::traits::ObligationCauseCode;
 use rustc_infer::{
     infer,
     traits::{self, Obligation},
@@ -22,7 +24,6 @@ use rustc_middle::ty::adjustment::{
 };
 use rustc_middle::ty::SubstsRef;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt};
-use rustc_span::def_id::LocalDefId;
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::Span;
 use rustc_target::spec::abi;
@@ -66,7 +67,7 @@ pub fn check_legal_trait_for_method_call(
 #[derive(Debug)]
 enum CallStep<'tcx> {
     Builtin(Ty<'tcx>),
-    DeferredClosure(LocalDefId, ty::FnSig<'tcx>),
+    DeferredClosure(Ty<'tcx>, ty::FnSig<'tcx>),
     /// E.g., enum variant constructors.
     Overloaded(MethodCallee<'tcx>),
 }
@@ -173,7 +174,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             closure_substs: substs,
                         },
                     );
-                    return Some(CallStep::DeferredClosure(def_id, closure_sig));
+                    return Some(CallStep::DeferredClosure(adjusted_ty, closure_sig));
                 }
             }
 
@@ -375,7 +376,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         arg_exprs: &'tcx [hir::Expr<'tcx>],
         expected: Expectation<'tcx>,
     ) -> Ty<'tcx> {
-        let (fn_sig, def_id) = match *callee_ty.kind() {
+        let fn_sig = match *callee_ty.kind() {
             ty::FnDef(def_id, subst) => {
                 let fn_sig = self.tcx.fn_sig(def_id).subst(self.tcx, subst);
 
@@ -403,9 +404,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             .emit();
                     }
                 }
-                (fn_sig, Some(def_id))
+                fn_sig
             }
-            ty::FnPtr(sig) => (sig, None),
+            ty::FnPtr(sig) => sig,
             _ => {
                 for arg in arg_exprs {
                     self.check_expr(arg);
@@ -459,7 +460,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             arg_exprs,
             fn_sig.c_variadic,
             TupleArgumentsFlag::DontTupleArguments,
-            def_id,
+            callee_ty,
+        );
+
+        self.check_callable(
+            call_expr.hir_id,
+            call_expr.span,
+            callee_ty,
+            fn_sig.inputs().iter().copied(),
         );
 
         if fn_sig.abi == abi::Abi::RustCall {
@@ -705,12 +713,37 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         err.emit()
     }
 
+    /// Enforces that things being called actually are callable
+    #[instrument(skip(self, arguments))]
+    pub(super) fn check_callable(
+        &self,
+        hir_id: hir::HirId,
+        span: Span,
+        callable_ty: Ty<'tcx>,
+        arguments: impl IntoIterator<Item = Ty<'tcx>>,
+    ) {
+        if callable_ty.references_error() {
+            return;
+        }
+
+        let cause = self.cause(span, ObligationCauseCode::MiscObligation);
+
+        let arguments_tuple = self.tcx.mk_tup_from_iter(arguments.into_iter());
+        let pred = ty::Binder::dummy(ty::TraitRef::from_lang_item(
+            self.tcx,
+            LangItem::Callable,
+            span,
+            [callable_ty, arguments_tuple],
+        ));
+        self.register_predicate(Obligation::new(self.tcx, cause, self.param_env, pred));
+    }
+
     fn confirm_deferred_closure_call(
         &self,
         call_expr: &'tcx hir::Expr<'tcx>,
         arg_exprs: &'tcx [hir::Expr<'tcx>],
         expected: Expectation<'tcx>,
-        closure_def_id: LocalDefId,
+        closure_ty: Ty<'tcx>,
         fn_sig: ty::FnSig<'tcx>,
     ) -> Ty<'tcx> {
         // `fn_sig` is the *signature* of the closure being called. We
@@ -733,7 +766,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             arg_exprs,
             fn_sig.c_variadic,
             TupleArgumentsFlag::TupleArguments,
-            Some(closure_def_id.to_def_id()),
+            closure_ty,
+        );
+
+        self.check_callable(
+            call_expr.hir_id,
+            call_expr.span,
+            closure_ty,
+            fn_sig.inputs()[0].tuple_fields(),
         );
 
         fn_sig.output()
@@ -804,6 +844,12 @@ impl<'a, 'tcx> DeferredCallResolution<'tcx> {
                 let mut adjustments = self.adjustments;
                 adjustments.extend(autoref);
                 fcx.apply_adjustments(self.callee_expr, adjustments);
+                fcx.check_callable(
+                    self.callee_expr.hir_id,
+                    self.callee_expr.span,
+                    fcx.tcx.mk_fn_def(method_callee.def_id, method_callee.substs),
+                    method_sig.inputs().iter().copied(),
+                );
 
                 fcx.write_method_call(self.call_expr.hir_id, method_callee);
             }

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -313,6 +313,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         result
     }
 
+    #[instrument(level = "trace", skip(self, span), ret)]
     pub(in super::super) fn normalize<T>(&self, span: Span, value: T) -> T
     where
         T: TypeFoldable<TyCtxt<'tcx>>,

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -94,14 +94,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expected: Expectation<'tcx>,
     ) -> Ty<'tcx> {
         let method = method.ok().filter(|method| !method.references_error());
-        let Some(method) = method else  {
+        let Some(method) = method else {
             let err_inputs = self.err_args(args_no_rcvr.len());
 
             let err_inputs = match tuple_arguments {
                 DontTupleArguments => err_inputs,
                 TupleArguments => vec![self.tcx.mk_tup(&err_inputs)],
             };
 
+            let err = self.tcx.ty_error_misc();
+            let callee_ty = method.map_or(err, |method| self.tcx.mk_fn_def(method.def_id, method.substs));
             self.check_argument_types(
                 sp,
                 expr,
@@ -110,9 +112,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 args_no_rcvr,
                 false,
                 tuple_arguments,
-                method.map(|method| method.def_id),
+                callee_ty,
             );
-            return self.tcx.ty_error_misc();
+            self.check_callable(expr.hir_id, sp, callee_ty, std::iter::once(err).chain(err_inputs));
+            return err;
         };
 
         // HACK(eddyb) ignore self in the definition (see above).
@@ -122,6 +125,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             method.sig.output(),
             &method.sig.inputs()[1..],
         );
+        let callee_ty = self.tcx.mk_fn_def(method.def_id, method.substs);
         self.check_argument_types(
             sp,
             expr,
@@ -130,14 +134,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             args_no_rcvr,
             method.sig.c_variadic,
             tuple_arguments,
-            Some(method.def_id),
+            callee_ty,
         );
 
+        self.check_callable(expr.hir_id, sp, callee_ty, method.sig.inputs().iter().copied());
+
         method.sig.output()
     }
 
     /// Generic function that factors out common logic from function calls,
     /// method calls and overloaded operators.
+    #[instrument(level = "trace", skip(self, call_expr, provided_args))]
     pub(in super::super) fn check_argument_types(
         &self,
         // Span enclosing the call site
@@ -154,8 +161,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         c_variadic: bool,
         // Whether the arguments have been bundled in a tuple (ex: closures)
         tuple_arguments: TupleArgumentsFlag,
-        // The DefId for the function being called, for better error messages
-        fn_def_id: Option<DefId>,
+        // The callee type (e.g. function item ZST, function pointer or closure).
+        // Note that this may have surprising function definitions, like often just
+        // referring to `FnOnce::call_once`, but with an appropriate `Self` type.
+        callee_ty: Ty<'tcx>,
     ) {
         let tcx = self.tcx;
 
@@ -230,7 +239,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let minimum_input_count = expected_input_tys.len();
         let provided_arg_count = provided_args.len();
 
-        let is_const_eval_select = matches!(fn_def_id, Some(def_id) if
+        let is_const_eval_select = matches!(*callee_ty.kind(), ty::FnDef(def_id, _) if
             self.tcx.def_kind(def_id) == hir::def::DefKind::Fn
             && self.tcx.is_intrinsic(def_id)
             && self.tcx.item_name(def_id) == sym::const_eval_select);
@@ -456,7 +465,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 provided_args,
                 c_variadic,
                 err_code,
-                fn_def_id,
+                match *callee_ty.kind() {
+                    ty::Generator(did, ..) | ty::Closure(did, _) | ty::FnDef(did, _) => Some(did),
+                    ty::FnPtr(..) | ty::Error(_) => None,
+                    ref kind => span_bug!(call_span, "invalid call argument type: {kind:?}"),
+                },
                 call_span,
                 call_expr,
             );

compiler/rustc_hir_typeck/src/lib.rs

@@ -430,7 +430,7 @@ fn report_unexpected_variant_res(
 /// # fn f(x: (isize, isize)) {}
 /// f((1, 2));
 /// ```
-#[derive(Copy, Clone, Eq, PartialEq)]
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
 enum TupleArgumentsFlag {
     DontTupleArguments,
     TupleArguments,

compiler/rustc_hir_typeck/src/method/confirm.rs

@@ -86,6 +86,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
         ConfirmContext { fcx, span, self_expr, call_expr, skip_record_for_diagnostics: false }
     }
 
+    #[instrument(level = "trace", skip(self), ret)]
     fn confirm(
         &mut self,
         unadjusted_self_ty: Ty<'tcx>,
@@ -99,7 +100,8 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
         let rcvr_substs = self.fresh_receiver_substs(self_ty, &pick);
         let all_substs = self.instantiate_method_substs(&pick, segment, rcvr_substs);
 
-        debug!("rcvr_substs={rcvr_substs:?}, all_substs={all_substs:?}");
+        debug!(?rcvr_substs);
+        debug!(?all_substs);
 
         // Create the final signature for the method, replacing late-bound regions.
         let (method_sig, method_predicates) = self.instantiate_method_sig(&pick, all_substs);
@@ -125,11 +127,9 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
         // could alter our Self-type, except for normalizing the receiver from the
         // signature (which is also done during probing).
         let method_sig_rcvr = self.normalize(self.span, method_sig.inputs()[0]);
-        debug!(
-            "confirm: self_ty={:?} method_sig_rcvr={:?} method_sig={:?} method_predicates={:?}",
-            self_ty, method_sig_rcvr, method_sig, method_predicates
-        );
+        debug!(?self_ty, ?method_sig_rcvr, ?pick);
         self.unify_receivers(self_ty, method_sig_rcvr, &pick, all_substs);
+        let inputs = method_sig.inputs();
 
         let (method_sig, method_predicates) =
             self.normalize(self.span, (method_sig, method_predicates));
@@ -150,6 +150,13 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
             );
         }
 
+        self.check_callable(
+            self.call_expr.hir_id,
+            self.span,
+            self.tcx.mk_fn_def(pick.item.def_id, all_substs),
+            inputs.iter().copied(),
+        );
+
         // Create the final `MethodCallee`.
         let callee = MethodCallee {
             def_id: pick.item.def_id,

compiler/rustc_hir_typeck/src/method/mod.rs

@@ -18,6 +18,7 @@ use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, DefKind, Namespace};
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::{self, InferOk};
+use rustc_macros::TypeVisitable;
 use rustc_middle::query::Providers;
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
@@ -33,7 +34,7 @@ pub fn provide(providers: &mut Providers) {
     probe::provide(providers);
 }
 
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Copy, Debug, TypeVisitable)]
 pub struct MethodCallee<'tcx> {
     /// Impl method ID, for inherent methods, or trait method ID, otherwise.
     pub def_id: DefId,

compiler/rustc_middle/src/ty/consts/int.rs

@@ -418,7 +418,7 @@ impl TryFrom<ScalarInt> for char {
 
     #[inline]
     fn try_from(int: ScalarInt) -> Result<Self, Self::Error> {
-        let Ok(bits) = int.to_bits(Size::from_bytes(std::mem::size_of::<char>())) else  {
+        let Ok(bits) = int.to_bits(Size::from_bytes(std::mem::size_of::<char>())) else {
             return Err(CharTryFromScalarInt);
         };
         match char::from_u32(bits.try_into().unwrap()) {

compiler/rustc_span/src/symbol.rs

@@ -450,6 +450,7 @@ symbols! {
         call,
         call_mut,
         call_once,
+        callable,
         caller_location,
         capture_disjoint_fields,
         cause,

compiler/rustc_trait_selection/src/solve/assembly/mod.rs

@@ -236,6 +236,12 @@ pub(super) trait GoalKind<'tcx>:
         goal: Goal<'tcx, Self>,
     ) -> QueryResult<'tcx>;
 
+    // `Callable` is implemented for all function items, function definitions and closures.
+    fn consider_builtin_callable_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx>;
+
     // A generator (that comes from an `async` desugaring) is known to implement
     // `Future<Output = O>`, where `O` is given by the generator's return type
     // that was computed during type-checking.
@@ -284,6 +290,7 @@ pub(super) trait GoalKind<'tcx>:
 }
 
 impl<'tcx> EvalCtxt<'_, 'tcx> {
+    #[instrument(level = "trace", skip(self), ret)]
     pub(super) fn assemble_and_evaluate_candidates<G: GoalKind<'tcx>>(
         &mut self,
         goal: Goal<'tcx, G>,
@@ -430,6 +437,8 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             G::consider_builtin_tuple_candidate(self, goal)
         } else if lang_items.pointee_trait() == Some(trait_def_id) {
             G::consider_builtin_pointee_candidate(self, goal)
+        } else if lang_items.callable_trait() == Some(trait_def_id) {
+            G::consider_builtin_callable_candidate(self, goal)
         } else if lang_items.future_trait() == Some(trait_def_id) {
             G::consider_builtin_future_candidate(self, goal)
         } else if lang_items.gen_trait() == Some(trait_def_id) {