rarw

Author: lcnr

compiler/rustc_hir_typeck/src/callee.rs

@@ -15,7 +15,7 @@ use rustc_middle::ty::adjustment::{
 use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt, TypeVisitableExt};
 use rustc_middle::{bug, span_bug};
 use rustc_span::def_id::LocalDefId;
-use rustc_span::{Span, sym};
+use rustc_span::{Span, Symbol, sym};
 use rustc_target::spec::{AbiMap, AbiMapping};
 use rustc_trait_selection::error_reporting::traits::DefIdOrName;
 use rustc_trait_selection::infer::InferCtxtExt as _;
@@ -78,7 +78,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             _ => self.check_expr(callee_expr),
         };
 
-        let expr_ty = self.structurally_resolve_type(call_expr.span, original_callee_ty);
+        let expr_ty = self.try_structurally_resolve_type(call_expr.span, original_callee_ty);
 
         let mut autoderef = self.autoderef(callee_expr.span, expr_ty);
         let mut result = None;
@@ -200,7 +200,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         arg_exprs: &'tcx [hir::Expr<'tcx>],
         autoderef: &Autoderef<'a, 'tcx>,
     ) -> Option<CallStep<'tcx>> {
-        let adjusted_ty = self.structurally_resolve_type(autoderef.span(), autoderef.final_ty());
+        let adjusted_ty =
+            self.try_structurally_resolve_type(autoderef.span(), autoderef.final_ty());
 
         // If the callee is a function pointer or a closure, then we're all set.
         match *adjusted_ty.kind() {
@@ -297,6 +298,24 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 return None;
             }
 
+            ty::Infer(ty::TyVar(vid)) => {
+                // If we end up with an inference variable which is not the hidden type of
+                // an opaque, emit an error.
+                if let Some(alias_ty) = self.find_opaque_type_related_to_vid(vid) {
+                    return self
+                        .try_overloaded_call_traits_for_alias(call_expr, alias_ty, arg_exprs)
+                        .map(|(autoref, method)| {
+                            let mut adjustments = self.adjust_steps(autoderef);
+                            adjustments.extend(autoref);
+                            self.apply_adjustments(callee_expr, adjustments);
+                            CallStep::Overloaded(method)
+                        });
+                } else {
+                    self.type_must_be_known_at_this_point(autoderef.span(), adjusted_ty);
+                    return None;
+                }
+            }
+
             ty::Error(_) => {
                 return None;
             }
@@ -401,6 +420,102 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         None
     }
 
+    fn try_overloaded_call_trait(
+        &self,
+        call_expr: &hir::Expr<'_>,
+        call_ty: Ty<'tcx>,
+        opt_arg_exprs: Option<&'tcx [hir::Expr<'tcx>]>,
+        opt_trait_def_id: Option<DefId>,
+        method_name: Symbol,
+        borrow: bool,
+    ) -> Option<(Option<Adjustment<'tcx>>, MethodCallee<'tcx>)> {
+        let Some(trait_def_id) = opt_trait_def_id else {
+            return None;
+        };
+
+        let opt_input_type = opt_arg_exprs.map(|arg_exprs| {
+            Ty::new_tup_from_iter(self.tcx, arg_exprs.iter().map(|e| self.next_ty_var(e.span)))
+        });
+
+        let Some(ok) = self.lookup_method_for_operator(
+            self.misc(call_expr.span),
+            method_name,
+            trait_def_id,
+            call_ty,
+            opt_input_type,
+        ) else {
+            return None;
+        };
+        let method = self.register_infer_ok_obligations(ok);
+        let mut autoref = None;
+        if borrow {
+            // Check for &self vs &mut self in the method signature. Since this is either
+            // the Fn or FnMut trait, it should be one of those.
+            let ty::Ref(_, _, mutbl) = *method.sig.inputs()[0].kind() else {
+                bug!("Expected `FnMut`/`Fn` to take receiver by-ref/by-mut")
+            };
+
+            // For initial two-phase borrow
+            // deployment, conservatively omit
+            // overloaded function call ops.
+            let mutbl = AutoBorrowMutability::new(mutbl, AllowTwoPhase::No);
+
+            autoref = Some(Adjustment {
+                kind: Adjust::Borrow(AutoBorrow::Ref(mutbl)),
+                target: method.sig.inputs()[0],
+            });
+        }
+
+        Some((autoref, method))
+    }
+
+    fn try_overloaded_call_traits_for_alias(
+        &self,
+        call_expr: &'tcx hir::Expr<'tcx>,
+        alias_ty: ty::AliasTy<'tcx>,
+        arg_exprs: &'tcx [rustc_hir::Expr<'tcx>],
+    ) -> Option<(Option<Adjustment<'tcx>>, MethodCallee<'tcx>)> {
+        let call_ty = alias_ty.to_ty(self.tcx);
+
+        let call_traits = [
+            (self.tcx.lang_items().fn_trait(), sym::call, true),
+            (self.tcx.lang_items().fn_mut_trait(), sym::call_mut, true),
+            (self.tcx.lang_items().fn_once_trait(), sym::call_once, false),
+            (self.tcx.lang_items().async_fn_trait(), sym::async_call, true),
+            (self.tcx.lang_items().async_fn_mut_trait(), sym::async_call_mut, true),
+            (self.tcx.lang_items().async_fn_once_trait(), sym::async_call_once, false),
+        ];
+        // We only want to try a call trait if it shows up in the bounds
+        // of the opaque. We confirm the first one that shows up in the
+        // bounds list, which can lead to inference weirdness but doesn't
+        // matter today.
+        for clause in
+            self.tcx.item_self_bounds(alias_ty.def_id).iter_instantiated(self.tcx, alias_ty.args)
+        {
+            let Some(poly_trait_ref) = clause.as_trait_clause() else {
+                continue;
+            };
+
+            if let Some(&(opt_trait_def_id, method_name, borrow)) =
+                call_traits.iter().find(|(trait_def_id, _, _)| {
+                    trait_def_id.is_some_and(|trait_def_id| trait_def_id == poly_trait_ref.def_id())
+                })
+                && let Some(confirmed) = self.try_overloaded_call_trait(
+                    call_expr,
+                    call_ty,
+                    Some(arg_exprs),
+                    opt_trait_def_id,
+                    method_name,
+                    borrow,
+                )
+            {
+                return Some(confirmed);
+            }
+        }
+
+        None
+    }
+
     /// Give appropriate suggestion when encountering `||{/* not callable */}()`, where the
     /// likely intention is to call the closure, suggest `(||{})()`. (#55851)
     fn identify_bad_closure_def_and_call(

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -1469,24 +1469,25 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     pub(crate) fn structurally_resolve_type(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
         let ty = self.try_structurally_resolve_type(sp, ty);
 
-        if !ty.is_ty_var() {
-            ty
-        } else {
-            let e = self.tainted_by_errors().unwrap_or_else(|| {
-                self.err_ctxt()
-                    .emit_inference_failure_err(
-                        self.body_id,
-                        sp,
-                        ty.into(),
-                        TypeAnnotationNeeded::E0282,
-                        true,
-                    )
-                    .emit()
-            });
-            let err = Ty::new_error(self.tcx, e);
-            self.demand_suptype(sp, err, ty);
-            err
-        }
+        if !ty.is_ty_var() { ty } else { self.type_must_be_known_at_this_point(sp, ty) }
+    }
+
+    #[cold]
+    pub(crate) fn type_must_be_known_at_this_point(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
+        let guar = self.tainted_by_errors().unwrap_or_else(|| {
+            self.err_ctxt()
+                .emit_inference_failure_err(
+                    self.body_id,
+                    sp,
+                    ty.into(),
+                    TypeAnnotationNeeded::E0282,
+                    true,
+                )
+                .emit()
+        });
+        let err = Ty::new_error(self.tcx, guar);
+        self.demand_suptype(sp, err, ty);
+        err
     }
 
     pub(crate) fn structurally_resolve_const(

compiler/rustc_infer/src/infer/mod.rs

@@ -1004,6 +1004,35 @@ impl<'tcx> InferCtxt<'tcx> {
         self.inner.borrow_mut().opaque_type_storage.iter_opaque_types().collect()
     }
 
+    /// Searches for an opaque type key whose hidden type is related to `ty_vid`.
+    ///
+    /// This only checks for a subtype relation, it does not require equality.
+    pub fn find_opaque_type_related_to_vid(&self, ty_vid: TyVid) -> Option<ty::AliasTy<'tcx>> {
+        // Avoid accidentally allowing more code to compile with the old solver.
+        if !self.next_trait_solver() {
+            return None;
+        }
+
+        let ty_sub_vid = self.sub_root_var(ty_vid);
+        let inner = &mut *self.inner.borrow_mut();
+        // This is iffy, can't call `type_variables()` as we're already
+        // borrowing the `opaque_type_storage` here.
+        let mut type_variables = inner.type_variable_storage.with_log(&mut inner.undo_log);
+        let opaque = inner
+            .opaque_type_storage
+            .iter_opaque_types()
+            .find(|(_, hidden_ty)| {
+                if let ty::Infer(ty::TyVar(hidden_vid)) = *hidden_ty.ty.kind() {
+                    let opaque_sub_vid = type_variables.sub_root_var(hidden_vid);
+                    opaque_sub_vid == ty_sub_vid
+                } else {
+                    false
+                }
+            })
+            .map(|(key, _)| ty::AliasTy::new_from_args(self.tcx, key.def_id.to_def_id(), key.args));
+        opaque
+    }
+
     #[inline(always)]
     pub fn can_define_opaque_ty(&self, id: impl Into<DefId>) -> bool {
         debug_assert!(!self.next_trait_solver());

tests/ui/impl-trait/non-defining-uses/method-call-on-infer.rs

@@ -0,0 +1,38 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@ check-pass
+
+fn fn_trait() -> impl Fn() {
+    if false {
+        let f = fn_trait();
+        f();
+    }
+
+    || ()
+}
+
+fn fn_mut() -> impl FnMut() -> usize {
+    if false {
+        let mut f = fn_mut();
+        f();
+    }
+    
+    let mut state = 0;
+    move || {
+        state += 1;
+        state
+    }
+}
+
+fn fn_once() -> impl FnOnce() {
+    if false {
+        let mut f = fn_once();
+        f();
+    }
+    
+    let string = String::new();
+    move || drop(string)
+}
+
+fn main() {}

tests/ui/inference/return-block-type-inference-15965.stderr

@@ -1,10 +1,8 @@
 error[E0282]: type annotations needed
   --> $DIR/return-block-type-inference-15965.rs:5:9
    |
-LL | /         { return () }
-LL | |
-LL | |     ()
-   | |______^ cannot infer type
+LL |         { return () }
+   |         ^^^^^^^^^^^^^ cannot infer type
 
 error: aborting due to 1 previous error
 

tests/ui/unboxed-closures/unboxed-closures-failed-recursive-fn-2.stderr

@@ -5,7 +5,7 @@ LL |     let mut closure0 = None;
    |         ^^^^^^^^^^^^
 ...
 LL |                         return c();
-   |                                --- type must be known at this point
+   |                                - type must be known at this point
    |
 help: consider giving `closure0` an explicit type, where the placeholders `_` are specified
    |