Deduplicate fn trait compatibility checks

compiler/rustc_middle/src/ty/sty.rs

@@ -23,7 +23,7 @@
 use rustc_span::symbol::{kw, sym, Symbol};
 use rustc_span::Span;
 use rustc_target::abi::VariantIdx;
-use rustc_target::spec::abi;
+use rustc_target::spec::abi::{self, Abi};
 use std::borrow::Cow;
 use std::cmp::Ordering;
 use std::fmt;
@@ -1403,6 +1403,18 @@ pub fn unsafety(&self) -> hir::Unsafety {
     pub fn abi(&self) -> abi::Abi {
         self.skip_binder().abi
     }
+
+    pub fn is_fn_trait_compatible(&self) -> bool {
+        matches!(
+            self.skip_binder(),
+            ty::FnSig {
+                unsafety: rustc_hir::Unsafety::Normal,
+                abi: Abi::Rust,
+                c_variadic: false,
+                ..
+            }
+        )
+    }
 }
 
 pub type CanonicalPolyFnSig<'tcx> = Canonical<'tcx, Binder<'tcx, FnSig<'tcx>>>;

compiler/rustc_trait_selection/src/solve/trait_goals/structural_traits.rs

@@ -2,7 +2,6 @@
 use rustc_hir::{def_id::DefId, Movability, Mutability};
 use rustc_infer::traits::query::NoSolution;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable};
-use rustc_target::spec::abi::Abi;
 
 use crate::solve::EvalCtxt;
 
@@ -197,13 +196,7 @@ pub(crate) fn extract_tupled_inputs_and_output_from_callable<'tcx>(
         )),
         // keep this in sync with assemble_fn_pointer_candidates until the old solver is removed.
         ty::FnPtr(sig) => {
-            if let ty::FnSig {
+            if sig.is_fn_trait_compatible() {
-                unsafety: rustc_hir::Unsafety::Normal,
-                abi: Abi::Rust,
-                c_variadic: false,
-                ..
-            } = sig.skip_binder()
-            {
                 Ok(Some(sig.map_bound(|sig| (tcx.mk_tup(sig.inputs()), sig.output()))))
             } else {
                 Err(NoSolution)

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -11,7 +11,6 @@
 use rustc_infer::traits::{Obligation, SelectionError, TraitObligation};
 use rustc_middle::ty::fast_reject::TreatProjections;
 use rustc_middle::ty::{self, Ty, TypeVisitableExt};
-use rustc_target::spec::abi::Abi;
 
 use crate::traits;
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
@@ -302,33 +301,21 @@ fn assemble_fn_pointer_candidates(
                 candidates.ambiguous = true; // Could wind up being a fn() type.
             }
             // Provide an impl, but only for suitable `fn` pointers.
-            ty::FnPtr(_) => {
+            ty::FnPtr(sig) => {
-                if let ty::FnSig {
+                if sig.is_fn_trait_compatible() {
-                    unsafety: hir::Unsafety::Normal,
-                    abi: Abi::Rust,
-                    c_variadic: false,
-                    ..
-                } = self_ty.fn_sig(self.tcx()).skip_binder()
-                {
                     candidates.vec.push(FnPointerCandidate { is_const: false });
                 }
             }
             // Provide an impl for suitable functions, rejecting `#[target_feature]` functions (RFC 2396).
             ty::FnDef(def_id, _) => {
-                if let ty::FnSig {
+                if self.tcx().fn_sig(def_id).skip_binder().is_fn_trait_compatible()
-                    unsafety: hir::Unsafety::Normal,
+                    && self.tcx().codegen_fn_attrs(def_id).target_features.is_empty()
-                    abi: Abi::Rust,
-                    c_variadic: false,
-                    ..
-                } = self_ty.fn_sig(self.tcx()).skip_binder()
                 {
-                    if self.tcx().codegen_fn_attrs(def_id).target_features.is_empty() {
                     candidates
                         .vec
                         .push(FnPointerCandidate { is_const: self.tcx().is_const_fn(def_id) });
                 }
             }
-            }
             _ => {}
         }
     }