mentioned_items: walk all types, not just consts

Author: RalfJung

compiler/rustc_middle/src/mir/mod.rs

@@ -45,6 +45,7 @@ use std::ops::{Index, IndexMut};
 use std::{iter, mem};
 
 pub use self::query::*;
+use self::visit::TyContext;
 pub use basic_blocks::BasicBlocks;
 
 mod basic_blocks;
@@ -607,6 +608,17 @@ impl<'tcx> Body<'tcx> {
         }
     }
 
+    pub fn span_for_ty_context(&self, ty_context: TyContext) -> Span {
+        match ty_context {
+            TyContext::UserTy(span) => span,
+            TyContext::ReturnTy(source_info)
+            | TyContext::LocalDecl { source_info, .. }
+            | TyContext::YieldTy(source_info)
+            | TyContext::ResumeTy(source_info) => source_info.span,
+            TyContext::Location(loc) => self.source_info(loc).span,
+        }
+    }
+
     /// Returns the return type; it always return first element from `local_decls` array.
     #[inline]
     pub fn return_ty(&self) -> Ty<'tcx> {

compiler/rustc_mir_transform/src/mentioned_items.rs

@@ -1,5 +1,6 @@
 use rustc_middle::mir::visit::Visitor;
-use rustc_middle::mir::{self, ConstOperand, Location, MentionedItem, MirPass};
+use rustc_middle::mir::{self, Location, MentionedItem, MirPass};
+use rustc_middle::ty::Ty;
 use rustc_middle::ty::{self, adjustment::PointerCoercion, TyCtxt};
 use rustc_session::Session;
 use rustc_span::source_map::Spanned;
@@ -30,14 +31,13 @@ impl<'tcx> MirPass<'tcx> for MentionedItems {
 }
 
 impl<'tcx> Visitor<'tcx> for MentionedItemsVisitor<'_, 'tcx> {
-    fn visit_constant(&mut self, constant: &ConstOperand<'tcx>, _: Location) {
-        let const_ = constant.const_;
-        // This is how function items get referenced: via constants of `FnDef` type. This handles
-        // both functions that are called and those that are just turned to function pointers.
-        if let ty::FnDef(def_id, args) = const_.ty().kind() {
+    fn visit_ty(&mut self, ty: Ty<'tcx>, ty_context: mir::visit::TyContext) {
+        if let ty::FnDef(def_id, args) = ty.kind() {
             debug!("adding to required_items: {def_id:?}");
-            self.mentioned_items
-                .push(Spanned { node: MentionedItem::Fn(*def_id, args), span: constant.span });
+            self.mentioned_items.push(Spanned {
+                node: MentionedItem::Fn(*def_id, args),
+                span: self.body.span_for_ty_context(ty_context),
+            });
         }
     }
 

tests/ui/consts/required-consts/collect-in-dead-closure.opt.stderr

@@ -16,7 +16,7 @@ note: the above error was encountered while instantiating `fn not_called::<i32>`
   --> $DIR/collect-in-dead-closure.rs:23:33
    |
 LL |         let _closure: fn() = || not_called::<T>();
-   |                                 ^^^^^^^^^^^^^^^
+   |                                 ^^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error
 

tests/ui/consts/required-consts/collect-in-dead-fn.opt.stderr

@@ -16,7 +16,7 @@ note: the above error was encountered while instantiating `fn not_called::<i32>`
   --> $DIR/collect-in-dead-fn.rs:25:9
    |
 LL |         not_called::<T>();
-   |         ^^^^^^^^^^^^^^^
+   |         ^^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error