Attempt to normalize FnDef signature in InferCtxt::cmp

compiler/rustc_infer/src/infer/at.rs

@@ -78,6 +78,10 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             err_count_on_creation: self.err_count_on_creation,
             in_snapshot: self.in_snapshot.clone(),
             universe: self.universe.clone(),
+            normalize_fn_sig_for_diagnostic: self
+                .normalize_fn_sig_for_diagnostic
+                .as_ref()
+                .map(|f| f.clone()),
         }
     }
 }

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -961,12 +961,23 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         }
     }
 
+    fn normalize_fn_sig_for_diagnostic(&self, sig: ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx> {
+        if let Some(normalize) = &self.normalize_fn_sig_for_diagnostic {
+            normalize(self, sig)
+        } else {
+            sig
+        }
+    }
+
     /// Given two `fn` signatures highlight only sub-parts that are different.
     fn cmp_fn_sig(
         &self,
         sig1: &ty::PolyFnSig<'tcx>,
         sig2: &ty::PolyFnSig<'tcx>,
     ) -> (DiagnosticStyledString, DiagnosticStyledString) {
+        let sig1 = &self.normalize_fn_sig_for_diagnostic(*sig1);
+        let sig2 = &self.normalize_fn_sig_for_diagnostic(*sig2);
+
         let get_lifetimes = |sig| {
             use rustc_hir::def::Namespace;
             let (_, sig, reg) = ty::print::FmtPrinter::new(self.tcx, Namespace::TypeNS)

compiler/rustc_infer/src/infer/mod.rs

@@ -337,6 +337,9 @@ pub struct InferCtxt<'a, 'tcx> {
     /// when we enter into a higher-ranked (`for<..>`) type or trait
     /// bound.
     universe: Cell<ty::UniverseIndex>,
+
+    normalize_fn_sig_for_diagnostic:
+        Option<Lrc<dyn Fn(&InferCtxt<'_, 'tcx>, ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx>>>,
 }
 
 /// See the `error_reporting` module for more details.
@@ -540,6 +543,8 @@ pub struct InferCtxtBuilder<'tcx> {
     defining_use_anchor: DefiningAnchor,
     considering_regions: bool,
     fresh_typeck_results: Option<RefCell<ty::TypeckResults<'tcx>>>,
+    normalize_fn_sig_for_diagnostic:
+        Option<Lrc<dyn Fn(&InferCtxt<'_, 'tcx>, ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx>>>,
 }
 
 pub trait TyCtxtInferExt<'tcx> {
@@ -553,6 +558,7 @@ impl<'tcx> TyCtxtInferExt<'tcx> for TyCtxt<'tcx> {
             defining_use_anchor: DefiningAnchor::Error,
             considering_regions: true,
             fresh_typeck_results: None,
+            normalize_fn_sig_for_diagnostic: None,
         }
     }
 }
@@ -582,6 +588,14 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
         self
     }
 
+    pub fn with_normalize_fn_sig_for_diagnostic(
+        mut self,
+        fun: Lrc<dyn Fn(&InferCtxt<'_, 'tcx>, ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx>>,
+    ) -> Self {
+        self.normalize_fn_sig_for_diagnostic = Some(fun);
+        self
+    }
+
     /// Given a canonical value `C` as a starting point, create an
     /// inference context that contains each of the bound values
     /// within instantiated as a fresh variable. The `f` closure is
@@ -611,6 +625,7 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
             defining_use_anchor,
             considering_regions,
             ref fresh_typeck_results,
+            ref normalize_fn_sig_for_diagnostic,
         } = *self;
         let in_progress_typeck_results = fresh_typeck_results.as_ref();
         f(InferCtxt {
@@ -629,6 +644,9 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
             in_snapshot: Cell::new(false),
             skip_leak_check: Cell::new(false),
             universe: Cell::new(ty::UniverseIndex::ROOT),
+            normalize_fn_sig_for_diagnostic: normalize_fn_sig_for_diagnostic
+                .as_ref()
+                .map(|f| f.clone()),
         })
     }
 }

compiler/rustc_typeck/src/check/inherited.rs

@@ -1,18 +1,22 @@
 use super::callee::DeferredCallResolution;
 
 use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::sync::Lrc;
 use rustc_hir as hir;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::HirIdMap;
 use rustc_infer::infer;
 use rustc_infer::infer::{InferCtxt, InferOk, TyCtxtInferExt};
+use rustc_infer::traits::TraitEngineExt as _;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::def_id::LocalDefIdMap;
 use rustc_span::{self, Span};
 use rustc_trait_selection::infer::InferCtxtExt as _;
-use rustc_trait_selection::traits::{self, ObligationCause, TraitEngine, TraitEngineExt};
+use rustc_trait_selection::traits::{
+    self, FulfillmentContext, ObligationCause, TraitEngine, TraitEngineExt as _,
+};
 
 use std::cell::RefCell;
 use std::ops::Deref;
@@ -84,7 +88,29 @@ impl<'tcx> Inherited<'_, 'tcx> {
             infcx: tcx
                 .infer_ctxt()
                 .ignoring_regions()
-                .with_fresh_in_progress_typeck_results(hir_owner),
+                .with_fresh_in_progress_typeck_results(hir_owner)
+                .with_normalize_fn_sig_for_diagnostic(Lrc::new(move |infcx, fn_sig| {
+                    if fn_sig.has_escaping_bound_vars() {
+                        return fn_sig;
+                    }
+                    infcx.probe(|_| {
+                        let traits::Normalized { value: normalized_fn_sig, obligations } =
+                            traits::normalize(
+                                &mut traits::SelectionContext::new(infcx),
+                                // FIXME(compiler-errors): This is probably not the right param-env...
+                                infcx.tcx.param_env(def_id),
+                                ObligationCause::dummy(),
+                                fn_sig,
+                            );
+                        let mut fulfillment_ctxt = FulfillmentContext::new_in_snapshot();
+                        fulfillment_ctxt.register_predicate_obligations(infcx, obligations);
+                        if fulfillment_ctxt.select_all_or_error(infcx).is_empty() {
+                            infcx.resolve_vars_if_possible(normalized_fn_sig)
+                        } else {
+                            fn_sig
+                        }
+                    })
+                })),
             def_id,
         }
     }

src/test/ui/mismatched_types/normalize-fn-sig.rs

@@ -0,0 +1,16 @@
+trait Foo {
+    type Bar;
+}
+
+impl<T> Foo for T {
+    type Bar = i32;
+}
+
+fn foo<T>(_: <T as Foo>::Bar, _: &'static <T as Foo>::Bar) {}
+
+fn needs_i32_ref_fn(_: fn(&'static i32, i32)) {}
+
+fn main() {
+    needs_i32_ref_fn(foo::<()>);
+    //~^ ERROR mismatched types
+}

src/test/ui/mismatched_types/normalize-fn-sig.stderr

@@ -0,0 +1,19 @@
+error[E0308]: mismatched types
+  --> $DIR/normalize-fn-sig.rs:14:22
+   |
+LL |     needs_i32_ref_fn(foo::<()>);
+   |     ---------------- ^^^^^^^^^ expected `&i32`, found `i32`
+   |     |
+   |     arguments to this function are incorrect
+   |
+   = note: expected fn pointer `fn(&'static i32, i32)`
+                 found fn item `fn(i32, &'static i32) {foo::<()>}`
+note: function defined here
+  --> $DIR/normalize-fn-sig.rs:11:4
+   |
+LL | fn needs_i32_ref_fn(_: fn(&'static i32, i32)) {}
+   |    ^^^^^^^^^^^^^^^^ ------------------------
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.