Fix typecks on some spurious fudged function input expectation

compiler/rustc_hir_typeck/src/callee.rs

@@ -7,6 +7,7 @@ use rustc_hir::def::{self, CtorKind, Namespace, Res};
 use rustc_hir::def_id::DefId;
 use rustc_hir::{self as hir, HirId, LangItem};
 use rustc_hir_analysis::autoderef::Autoderef;
+use rustc_hir_analysis::hir_ty_lowering::IsMethodCall;
 use rustc_infer::infer::BoundRegionConversionTime;
 use rustc_infer::traits::{Obligation, ObligationCause, ObligationCauseCode};
 use rustc_middle::ty::adjustment::{
@@ -573,6 +574,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self.check_argument_types(
             call_expr.span,
             call_expr,
+            IsMethodCall::No,
             fn_sig.inputs(),
             fn_sig.output(),
             expected,
@@ -883,6 +885,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self.check_argument_types(
             call_expr.span,
             call_expr,
+            IsMethodCall::No,
             fn_sig.inputs(),
             fn_sig.output(),
             expected,
@@ -962,6 +965,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self.check_argument_types(
             call_expr.span,
             call_expr,
+            IsMethodCall::Yes,
             &method.sig.inputs()[1..],
             method.sig.output(),
             expected,

compiler/rustc_hir_typeck/src/expr.rs

@@ -21,7 +21,7 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::{ExprKind, HirId, QPath, find_attr, is_range_literal};
 use rustc_hir_analysis::NoVariantNamed;
-use rustc_hir_analysis::hir_ty_lowering::HirTyLowerer as _;
+use rustc_hir_analysis::hir_ty_lowering::{HirTyLowerer as _, IsMethodCall};
 use rustc_infer::infer::{self, DefineOpaqueTypes, InferOk, RegionVariableOrigin};
 use rustc_infer::traits::query::NoSolution;
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AllowTwoPhase};
@@ -1494,6 +1494,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 self.check_argument_types(
                     segment.ident.span,
                     expr,
+                    IsMethodCall::Yes,
                     &method.sig.inputs()[1..],
                     method.sig.output(),
                     expected,
@@ -1516,6 +1517,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 self.check_argument_types(
                     segment.ident.span,
                     expr,
+                    IsMethodCall::Yes,
                     &err_inputs,
                     err_output,
                     NoExpectation,

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -10,7 +10,7 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::{Expr, ExprKind, HirId, LangItem, Node, QPath, is_range_literal};
 use rustc_hir_analysis::check::potentially_plural_count;
-use rustc_hir_analysis::hir_ty_lowering::{HirTyLowerer, PermitVariants};
+use rustc_hir_analysis::hir_ty_lowering::{HirTyLowerer, IsMethodCall, PermitVariants};
 use rustc_index::IndexVec;
 use rustc_infer::infer::{BoundRegionConversionTime, DefineOpaqueTypes, InferOk, TypeTrace};
 use rustc_middle::ty::adjustment::AllowTwoPhase;
@@ -195,6 +195,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         call_span: Span,
         // Expression of the call site
         call_expr: &'tcx hir::Expr<'tcx>,
+        is_method: IsMethodCall,
         // Types (as defined in the *signature* of the target function)
         formal_input_tys: &[Ty<'tcx>],
         formal_output: Ty<'tcx>,
@@ -206,7 +207,8 @@ 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
+        // The DefId for the function being called, for callee bound checks and
+        // better error messages
         fn_def_id: Option<DefId>,
     ) {
         let tcx = self.tcx;
@@ -305,12 +307,104 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 })
                 .ok()
             })
-            .unwrap_or_default();
+            .unwrap_or_default()
+            .and_then(|expected_input_tys: Vec<Ty<'_>>| {
+                // Check the well-formedness of expected input tys, as using ill-formed
+                // expectation may cause type inference errors.
+                let well_formed = self.probe(|_| {
+                    let ocx = ObligationCtxt::new(self);
+                    for &ty in &expected_input_tys {
+                        ocx.register_obligation(traits::Obligation::new(
+                            self.tcx,
+                            self.misc(call_span),
+                            self.param_env,
+                            ty::ClauseKind::WellFormed(ty.into()),
+                        ));
+                    }
+                    ocx.try_evaluate_obligations().is_empty()
+                });
+                well_formed.then_some(expected_input_tys)
+            });
 
         let mut err_code = E0061;
 
+        let mut expected_meets_callee_bounds = Vec::with_capacity(formal_input_tys.len());
+        expected_meets_callee_bounds.resize(formal_input_tys.len(), true);
+
+        // Check whether the expected inputs satisfy the callee's where bounds.
+        // This is skipped for the old solver: attempting trait solving there can
+        // trigger an overflow, which is a fatal error in the old solver but is
+        // treated as mere ambiguity by the next solver.
+        if self.next_trait_solver()
+            && let Some(expected_input_tys) = &expected_input_tys
+            && let Some(fn_def_id) = fn_def_id
+            // We don't need to check bounds for closures as they are already in the current
+            // body's param env.
+            && self.tcx.def_kind(fn_def_id) != DefKind::Closure
+        {
+            self.probe(|_| {
+                let new_args = self.fresh_args_for_item(call_span, fn_def_id);
+                let fn_sig = self.tcx.fn_sig(fn_def_id).instantiate(self.tcx, new_args);
+                let fn_sig = self.instantiate_binder_with_fresh_vars(
+                    call_span,
+                    BoundRegionConversionTime::FnCall,
+                    fn_sig,
+                );
+                let ocx = ObligationCtxt::new(self);
+                let origin = self.misc(call_span);
+                let fn_sig = ocx.normalize(&origin, self.param_env, fn_sig);
+
+                let bound_input_tys = fn_sig.inputs();
+                let bound_input_tys = if is_method == IsMethodCall::Yes {
+                    &bound_input_tys[1..]
+                } else {
+                    &bound_input_tys[..]
+                };
+
+                let fn_bounds = self.tcx.predicates_of(fn_def_id).instantiate(self.tcx, new_args);
+                let fn_bounds = traits::predicates_for_generics(
+                    |_, sp| self.misc(sp),
+                    self.param_env,
+                    fn_bounds,
+                );
+                ocx.register_obligations(fn_bounds);
+
+                // perf: We reuse this by cloning rather than repeating the above lines
+                let preds = ocx.into_pending_obligations();
+
+                assert_eq!(bound_input_tys.len(), formal_input_tys.len(),);
+                for idx in 0..formal_input_tys.len() {
+                    let meets_bounds = self
+                        .probe(|_| {
+                            let ocx = ObligationCtxt::new(self);
+                            ocx.register_obligations(preds.clone());
+                            ocx.eq(
+                                &origin,
+                                self.param_env,
+                                bound_input_tys[idx],
+                                expected_input_tys[idx],
+                            )?;
+                            if ocx.try_evaluate_obligations().is_empty() {
+                                Ok(())
+                            } else {
+                                Err(TypeError::Mismatch)
+                            }
+                        })
+                        .is_ok();
+                    expected_meets_callee_bounds[idx] = meets_bounds;
+                }
+            });
+        }
+
         // If the arguments should be wrapped in a tuple (ex: closures), unwrap them here
         let (formal_input_tys, expected_input_tys) = if tuple_arguments == TupleArguments {
+            // Since the expected inputs are unpacked from a single tuple,
+            // each input meets the callee bounds if and only if the tuple does.
+            expected_meets_callee_bounds.resize(
+                provided_args.len(),
+                expected_meets_callee_bounds.first().copied().unwrap_or(true),
+            );
+
             let tuple_type = self.structurally_resolve_type(call_span, formal_input_tys[0]);
             match tuple_type.kind() {
                 // We expected a tuple and got a tuple
@@ -373,7 +467,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // We're on the happy path here, so we'll do a more involved check and write back types
             // To check compatibility, we'll do 3 things:
             // 1. Unify the provided argument with the expected type
-            let expectation = Expectation::rvalue_hint(self, expected_input_ty);
+            let expectation = if expected_meets_callee_bounds[idx] {
+                Expectation::rvalue_hint(self, expected_input_ty)
+            } else {
+                // If the expected input does not satisfy the callee's bounds, we must
+                // weaken the expectation; otherwise, coercing to a type that violates
+                // those bounds would result in a type mismatch.
+                // See https://github.com/rust-lang/rust/issues/149379.
+                Expectation::ExpectRvalueLikeUnsized(expected_input_ty)
+            };
 
             let checked_ty = self.check_expr_with_expectation(provided_arg, expectation);
 

tests/ui/coercion/fudge-inference/expectated-input-not-satisfying-fn-bounds-issue-149881.current.stderr

@@ -0,0 +1,22 @@
+error[E0277]: the size for values of type `[{integer}]` cannot be known at compilation time
+  --> $DIR/expectated-input-not-satisfying-fn-bounds-issue-149881.rs:16:24
+   |
+LL |     <[_]>::into_vec(id(Box::new([0, 1, 2])));
+   |                     -- ^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |                     |
+   |                     required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[{integer}]`
+note: required by an implicit `Sized` bound in `id`
+  --> $DIR/expectated-input-not-satisfying-fn-bounds-issue-149881.rs:11:7
+   |
+LL | fn id<T>(x: Box<T>) -> Box<T> {
+   |       ^ required by the implicit `Sized` requirement on this type parameter in `id`
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | fn id<T: ?Sized>(x: Box<T>) -> Box<T> {
+   |        ++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/coercion/fudge-inference/expectated-input-not-satisfying-fn-bounds-issue-149881.rs

@@ -0,0 +1,18 @@
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
+
+// FIXME(#149379): This should pass, but fails due to fudged expactation
+// types which are potentially not well-formed or for whom the function
+// where-bounds don't actually hold. And this results in weird bugs when
+// later treating these expectations as if they were actually correct..
+
+fn id<T>(x: Box<T>) -> Box<T> {
+    x
+}
+
+fn main() {
+    <[_]>::into_vec(id(Box::new([0, 1, 2])));
+    //[current]~^ ERROR: the size for values of type `[{integer}]` cannot be known at compilation time
+}

tests/ui/coercion/fudge-inference/expectated-input-not-satisfying-fn-bounds-issue-89299.current.stderr

@@ -0,0 +1,16 @@
+error[E0277]: `dyn Trait + Send` cannot be unpinned
+  --> $DIR/expectated-input-not-satisfying-fn-bounds-issue-89299.rs:21:27
+   |
+LL |     let _x = Foo(Pin::new(&mut a));
+   |                  -------- ^^^^^^ the trait `Unpin` is not implemented for `dyn Trait + Send`
+   |                  |
+   |                  required by a bound introduced by this call
+   |
+   = note: consider using the `pin!` macro
+           consider using `Box::pin` if you need to access the pinned value outside of the current scope
+note: required by a bound in `Pin::<Ptr>::new`
+  --> $SRC_DIR/core/src/pin.rs:LL:COL
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/coercion/fudge-inference/expectated-input-not-satisfying-fn-bounds-issue-89299.rs

@@ -0,0 +1,23 @@
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
+
+// FIXME(#149379): This should pass, but fails due to fudged expactation
+// types which are potentially not well-formed or for whom the function
+// where-bounds don't actually hold. And this results in weird bugs when
+// later treating these expectations as if they were actually correct..
+
+use std::pin::Pin;
+
+trait Trait {}
+
+impl Trait for i32 {}
+
+struct Foo<'a>(Pin<&'a mut (dyn Trait + Send)>);
+
+fn main() {
+    let mut a = 1;
+    let _x = Foo(Pin::new(&mut a));
+    //[current]~^ ERROR: `dyn Trait + Send` cannot be unpinned
+}

tests/ui/coercion/fudge-inference/fn-ret-trait-object-propagated-to-inputs-issue-149379-1.rs

@@ -1,11 +1,9 @@
 //@ revisions: current next
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
+//@ check-pass
 
-// FIXME(#149379): This should pass, but fails due to fudged expactation
-// types which are potentially not well-formed or for whom the function
-// where-bounds don't actually hold. And this results in weird bugs when
-// later treating these expectations as if they were actually correct..
+// A regression test for https://github.com/rust-lang/rust/issues/149379.
 
 fn foo<T>(x: (T, ())) -> Box<T> {
     Box::new(x.0)
@@ -14,6 +12,4 @@ fn foo<T>(x: (T, ())) -> Box<T> {
 fn main() {
     // Uses expectation as its struct tail is sized, resulting in `(dyn Send, ())`
     let _: Box<dyn Send> = foo(((), ()));
-    //~^ ERROR mismatched types
-    //~| ERROR the size for values of type `dyn Send` cannot be known at compilation time
 }

tests/ui/coercion/fudge-inference/fn-ret-trait-object-propagated-to-inputs-issue-149379-2.current.stderr

@@ -1,5 +1,5 @@
 error[E0277]: the size for values of type `dyn Send` cannot be known at compilation time
-  --> $DIR/fn-ret-trait-object-propagated-to-inputs-issue-149379-2.rs:15:38
+  --> $DIR/fn-ret-trait-object-propagated-to-inputs-issue-149379-2.rs:16:38
    |
 LL |     let _: Box<dyn Send> = sized_box(Box::new(1));
    |                            --------- ^^^^^^^^^^^ doesn't have a size known at compile-time
@@ -8,7 +8,7 @@ LL |     let _: Box<dyn Send> = sized_box(Box::new(1));
    |
    = help: the trait `Sized` is not implemented for `dyn Send`
 note: required by an implicit `Sized` bound in `sized_box`
-  --> $DIR/fn-ret-trait-object-propagated-to-inputs-issue-149379-2.rs:10:14
+  --> $DIR/fn-ret-trait-object-propagated-to-inputs-issue-149379-2.rs:11:14
    |
 LL | fn sized_box<T>(x: Box<T>) -> Box<T> {
    |              ^ required by the implicit `Sized` requirement on this type parameter in `sized_box`