Clean up infer_return_ty_for_fn_sig

compiler/rustc_hir_analysis/src/collect.rs

@@ -1330,7 +1330,7 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_, ty::PolyFn
             ..
         })
         | Item(hir::Item { kind: ItemKind::Fn(sig, generics, _), .. }) => {
-            infer_return_ty_for_fn_sig(sig, generics, def_id, &icx)
+            lower_fn_sig_recovering_infer_ret_ty(&icx, sig, generics, def_id)
         }
 
         ImplItem(hir::ImplItem { kind: ImplItemKind::Fn(sig, _), generics, .. }) => {
@@ -1347,7 +1347,7 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_, ty::PolyFn
                     None,
                 )
             } else {
-                infer_return_ty_for_fn_sig(sig, generics, def_id, &icx)
+                lower_fn_sig_recovering_infer_ret_ty(&icx, sig, generics, def_id)
             }
         }
 
@@ -1397,18 +1397,37 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_, ty::PolyFn
     ty::EarlyBinder::bind(output)
 }
 
-fn infer_return_ty_for_fn_sig<'tcx>(
+fn lower_fn_sig_recovering_infer_ret_ty<'tcx>(
-    sig: &hir::FnSig<'tcx>,
-    generics: &hir::Generics<'_>,
-    def_id: LocalDefId,
     icx: &ItemCtxt<'tcx>,
+    sig: &'tcx hir::FnSig<'tcx>,
+    generics: &'tcx hir::Generics<'tcx>,
+    def_id: LocalDefId,
+) -> ty::PolyFnSig<'tcx> {
+    if let Some(infer_ret_ty) = sig.decl.output.get_infer_ret_ty() {
+        return recover_infer_ret_ty(icx, infer_ret_ty, generics, def_id);
+    }
+
+    icx.lowerer().lower_fn_ty(
+        icx.tcx().local_def_id_to_hir_id(def_id),
+        sig.header.safety,
+        sig.header.abi,
+        sig.decl,
+        Some(generics),
+        None,
+    )
+}
+
+fn recover_infer_ret_ty<'tcx>(
+    icx: &ItemCtxt<'tcx>,
+    infer_ret_ty: &'tcx hir::Ty<'tcx>,
+    generics: &'tcx hir::Generics<'tcx>,
+    def_id: LocalDefId,
 ) -> ty::PolyFnSig<'tcx> {
     let tcx = icx.tcx;
     let hir_id = tcx.local_def_id_to_hir_id(def_id);
 
-    match sig.decl.output.get_infer_ret_ty() {
-        Some(ty) => {
     let fn_sig = tcx.typeck(def_id).liberated_fn_sigs()[hir_id];
+
     // Typeck doesn't expect erased regions to be returned from `type_of`.
     // This is a heuristic approach. If the scope has region parameters,
     // we should change fn_sig's lifetime from `ReErased` to `ReError`,
@@ -1433,18 +1452,18 @@ fn infer_return_ty_for_fn_sig<'tcx>(
     });
 
     let mut visitor = HirPlaceholderCollector::default();
-            visitor.visit_ty(ty);
+    visitor.visit_ty(infer_ret_ty);
 
     let mut diag = bad_placeholder(icx.lowerer(), visitor.0, "return type");
     let ret_ty = fn_sig.output();
+
     // Don't leak types into signatures unless they're nameable!
     // For example, if a function returns itself, we don't want that
     // recursive function definition to leak out into the fn sig.
     let mut recovered_ret_ty = None;
-
     if let Some(suggestable_ret_ty) = ret_ty.make_suggestable(tcx, false, None) {
         diag.span_suggestion(
-                    ty.span,
+            infer_ret_ty.span,
             "replace with the correct return type",
             suggestable_ret_ty,
             Applicability::MachineApplicable,
@@ -1456,7 +1475,7 @@ fn infer_return_ty_for_fn_sig<'tcx>(
         ret_ty,
     ) {
         diag.span_suggestion(
-                    ty.span,
+            infer_ret_ty.span,
             "replace with an appropriate return type",
             sugg,
             Applicability::MachineApplicable,
@@ -1464,6 +1483,7 @@ fn infer_return_ty_for_fn_sig<'tcx>(
     } else if ret_ty.is_closure() {
         diag.help("consider using an `Fn`, `FnMut`, or `FnOnce` trait bound");
     }
+
     // Also note how `Fn` traits work just in case!
     if ret_ty.is_closure() {
         diag.note(
@@ -1471,7 +1491,6 @@ fn infer_return_ty_for_fn_sig<'tcx>(
                      https://doc.rust-lang.org/book/ch13-01-closures.html",
         );
     }
-
     let guar = diag.emit();
     ty::Binder::dummy(tcx.mk_fn_sig(
         fn_sig.inputs().iter().copied(),
@@ -1480,16 +1499,6 @@ fn infer_return_ty_for_fn_sig<'tcx>(
         fn_sig.safety,
         fn_sig.abi,
     ))
-        }
-        None => icx.lowerer().lower_fn_ty(
-            hir_id,
-            sig.header.safety,
-            sig.header.abi,
-            sig.decl,
-            Some(generics),
-            None,
-        ),
-    }
 }
 
 pub fn suggest_impl_trait<'tcx>(