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;
@@ -30,22 +31,21 @@ 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),
+            });
         }
     }
 
     fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) {
         self.super_terminator(terminator, location);
         match terminator.kind {
             // We don't need to handle `Call` as we already handled all function type operands in
-            // `visit_constant`. But we do need to handle `Drop`.
+            // `visit_ty`. But we do need to handle `Drop`.
             mir::TerminatorKind::Drop { place, .. } => {
                 let ty = place.ty(self.body, self.tcx).ty;
                 let span = self.body.source_info(location).span;
@@ -90,7 +90,7 @@ impl<'tcx> Visitor<'tcx> for MentionedItemsVisitor<'_, 'tcx> {
                     _ => bug!(),
                 }
             }
-            // Function pointer casts are already handled by `visit_constant` above.
+            // Function pointer casts are already handled by `visit_ty` above.
             _ => {}
         }
     }

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-behind-generic.noopt.stderr

@@ -0,0 +1,20 @@
+error[E0080]: evaluation of `Fail::<i32>::C` failed
+  --> $DIR/collect-in-dead-fn-behind-generic.rs:8:19
+   |
+LL |     const C: () = panic!();
+   |                   ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/collect-in-dead-fn-behind-generic.rs:8:19
+   |
+   = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+note: erroneous constant encountered
+  --> $DIR/collect-in-dead-fn-behind-generic.rs:13:17
+   |
+LL |         let _ = Fail::<T>::C;
+   |                 ^^^^^^^^^^^^
+
+note: the above error was encountered while instantiating `fn not_called::<i32>`
+  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0080`.

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

@@ -0,0 +1,23 @@
+error[E0080]: evaluation of `Fail::<i32>::C` failed
+  --> $DIR/collect-in-dead-fn-behind-generic.rs:8:19
+   |
+LL |     const C: () = panic!();
+   |                   ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/collect-in-dead-fn-behind-generic.rs:8:19
+   |
+   = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+note: erroneous constant encountered
+  --> $DIR/collect-in-dead-fn-behind-generic.rs:13:17
+   |
+LL |         let _ = Fail::<T>::C;
+   |                 ^^^^^^^^^^^^
+
+note: the above error was encountered while instantiating `fn not_called::<i32>`
+  --> $DIR/collect-in-dead-fn-behind-generic.rs:25:9
+   |
+LL |         callit_not(not_called::<i32>)
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0080`.

tests/ui/consts/required-consts/collect-in-dead-fn-behind-generic.rs

@@ -0,0 +1,27 @@
+//@revisions: noopt opt
+//@ build-fail
+//@[opt] compile-flags: -O
+//! This fails without optimizations, so it should also fail with optimizations.
+
+struct Fail<T>(T);
+impl<T> Fail<T> {
+    const C: () = panic!(); //~ERROR evaluation of `Fail::<i32>::C` failed
+}
+
+fn not_called<T>() {
+    if false {
+        let _ = Fail::<T>::C;
+    }
+}
+
+fn callit_not(f: impl Fn()) {
+    if false {
+        f();
+    }
+}
+
+fn main() {
+    if false {
+        callit_not(not_called::<i32>)
+    }
+}

tests/ui/consts/required-consts/collect-in-dead-fn-behind-opaque-type.noopt.stderr

@@ -0,0 +1,20 @@
+error[E0080]: evaluation of `m::Fail::<i32>::C` failed
+  --> $DIR/collect-in-dead-fn-behind-opaque-type.rs:10:23
+   |
+LL |         const C: () = panic!();
+   |                       ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/collect-in-dead-fn-behind-opaque-type.rs:10:23
+   |
+   = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+note: erroneous constant encountered
+  --> $DIR/collect-in-dead-fn-behind-opaque-type.rs:17:21
+   |
+LL |             let _ = Fail::<T>::C;
+   |                     ^^^^^^^^^^^^
+
+note: the above error was encountered while instantiating `fn m::not_called::<i32>`
+  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0080`.

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

@@ -0,0 +1,23 @@
+error[E0080]: evaluation of `m::Fail::<i32>::C` failed
+  --> $DIR/collect-in-dead-fn-behind-opaque-type.rs:10:23
+   |
+LL |         const C: () = panic!();
+   |                       ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/collect-in-dead-fn-behind-opaque-type.rs:10:23
+   |
+   = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+note: erroneous constant encountered
+  --> $DIR/collect-in-dead-fn-behind-opaque-type.rs:17:21
+   |
+LL |             let _ = Fail::<T>::C;
+   |                     ^^^^^^^^^^^^
+
+note: the above error was encountered while instantiating `fn m::not_called::<i32>`
+  --> $DIR/collect-in-dead-fn-behind-opaque-type.rs:32:42
+   |
+LL |         let x: m::NotCalledFn = unsafe { std::mem::transmute(()) };
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0080`.

tests/ui/consts/required-consts/collect-in-dead-fn-behind-opaque-type.rs

@@ -0,0 +1,35 @@
+//@revisions: noopt opt
+//@ build-fail
+//@[opt] compile-flags: -O
+//! This fails without optimizations, so it should also fail with optimizations.
+#![feature(type_alias_impl_trait)]
+
+mod m {
+    struct Fail<T>(T);
+    impl<T> Fail<T> {
+        const C: () = panic!(); //~ERROR evaluation of `m::Fail::<i32>::C` failed
+    }
+
+    pub type NotCalledFn = impl Fn();
+
+    fn not_called<T>() {
+        if false {
+            let _ = Fail::<T>::C;
+        }
+    }
+
+    fn mk_not_called() -> NotCalledFn {
+        not_called::<i32>
+    }
+}
+
+fn main() {
+    // This does not involve a constant of `FnDef` type, it generates the value via unsafe
+    // shenanigans instead. This ensures that we check all `FnDef` types that occur in a function,
+    // not just those of constants. Furthermore the `FnDef` is behind an opaque type which bust be
+    // normalized away to reveal the function type.
+    if false {
+        let x: m::NotCalledFn = unsafe { std::mem::transmute(()) };
+        x();
+    }
+}

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