const checks: avoid 'top-level scope' terminology

Author: RalfJung

compiler/rustc_const_eval/messages.ftl

@@ -125,16 +125,11 @@ const_eval_incompatible_types =
     calling a function with argument of type {$callee_ty} passing data of type {$caller_ty}
 
 const_eval_interior_mutable_borrow_escaping =
-    interior mutable shared borrows of lifetime-extended temporaries in the top-level scope of a {const_eval_const_context} are not allowed
-    .label = this borrow of an interior mutable value refers to a lifetime-extended temporary
-    .help = to fix this, the value can be extracted to a separate `static` item and then referenced
-    .teach_note =
-        This creates a raw pointer to a temporary that has its lifetime extended to last for the entire program.
-        Lifetime-extended temporaries in constants and statics must be immutable.
-        This is to avoid accidentally creating shared mutable state.
-
-
-        If you really want global mutable state, try using an interior mutable `static` or a `static mut`.
+    interior mutable shared borrows of temporaries that have their lifetime extended until the end of the program are not allowed
+    .label = this borrow of an interior mutable value refers to such a temporary
+    .note = Temporaries in constants and statics can have their lifetime extended until the end of the program
+    .note2 = To avoid accidentally creating global mutable state, such temporaries must be immutable
+    .help = If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
 const_eval_intern_kind = {$kind ->
     [static] static
@@ -215,14 +210,11 @@ const_eval_modified_global =
     modifying a static's initial value from another static's initializer
 
 const_eval_mutable_borrow_escaping =
-    mutable borrows of lifetime-extended temporaries in the top-level scope of a {const_eval_const_context} are not allowed
-    .teach_note =
-        This creates a reference to a temporary that has its lifetime extended to last for the entire program.
-        Lifetime-extended temporaries in constants and statics must be immutable.
-        This is to avoid accidentally creating shared mutable state.
-
-
-        If you really want global mutable state, try using an interior mutable `static` or a `static mut`.
+    mutable borrows of temporaries that have their lifetime extended until the end of the program are not allowed
+    .label = this mutable borrow refers to such a temporary
+    .note = Temporaries in constants and statics can have their lifetime extended until the end of the program
+    .note2 = To avoid accidentally creating global mutable state, such temporaries must be immutable
+    .help = If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
 const_eval_mutable_ptr_in_final = encountered mutable pointer in final value of {const_eval_intern_kind}
 

compiler/rustc_const_eval/src/check_consts/ops.rs

@@ -567,12 +567,7 @@ impl<'tcx> NonConstOp<'tcx> for EscapingCellBorrow {
         DiagImportance::Secondary
     }
     fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> Diag<'tcx> {
-        ccx.dcx().create_err(errors::InteriorMutableBorrowEscaping {
-            span,
-            opt_help: matches!(ccx.const_kind(), hir::ConstContext::Static(_)),
-            kind: ccx.const_kind(),
-            teach: ccx.tcx.sess.teach(E0492),
-        })
+        ccx.dcx().create_err(errors::InteriorMutableBorrowEscaping { span, kind: ccx.const_kind() })
     }
 }
 
@@ -594,11 +589,7 @@ impl<'tcx> NonConstOp<'tcx> for EscapingMutBorrow {
     }
 
     fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> Diag<'tcx> {
-        ccx.dcx().create_err(errors::MutableBorrowEscaping {
-            span,
-            kind: ccx.const_kind(),
-            teach: ccx.tcx.sess.teach(E0764),
-        })
+        ccx.dcx().create_err(errors::MutableBorrowEscaping { span, kind: ccx.const_kind() })
     }
 }
 

compiler/rustc_const_eval/src/errors.rs

@@ -151,12 +151,14 @@ pub(crate) struct UnmarkedIntrinsicExposed {
 
 #[derive(Diagnostic)]
 #[diag(const_eval_mutable_borrow_escaping, code = E0764)]
+#[note]
+#[note(const_eval_note2)]
+#[help]
 pub(crate) struct MutableBorrowEscaping {
     #[primary_span]
+    #[label]
     pub span: Span,
     pub kind: ConstContext,
-    #[note(const_eval_teach_note)]
-    pub teach: bool,
 }
 
 #[derive(Diagnostic)]
@@ -217,15 +219,14 @@ pub(crate) struct UnallowedInlineAsm {
 
 #[derive(Diagnostic)]
 #[diag(const_eval_interior_mutable_borrow_escaping, code = E0492)]
+#[note]
+#[note(const_eval_note2)]
+#[help]
 pub(crate) struct InteriorMutableBorrowEscaping {
     #[primary_span]
     #[label]
     pub span: Span,
-    #[help]
-    pub opt_help: bool,
     pub kind: ConstContext,
-    #[note(const_eval_teach_note)]
-    pub teach: bool,
 }
 
 #[derive(LintDiagnostic)]

tests/ui/consts/const-mut-refs/issue-76510.rs

@@ -1,7 +1,7 @@
 use std::mem::{transmute, ManuallyDrop};
 
 const S: &'static mut str = &mut " hello ";
-//~^ ERROR: mutable borrows of lifetime-extended temporaries
+//~^ ERROR: mutable borrows of temporaries
 
 const fn trigger() -> [(); unsafe {
         let s = transmute::<(*const u8, usize), &ManuallyDrop<str>>((S.as_ptr(), 3));

tests/ui/consts/const-mut-refs/issue-76510.stderr

@@ -1,8 +1,12 @@
-error[E0764]: mutable borrows of lifetime-extended temporaries in the top-level scope of a constant are not allowed
+error[E0764]: mutable borrows of temporaries that have their lifetime extended until the end of the program are not allowed
   --> $DIR/issue-76510.rs:3:29
    |
 LL | const S: &'static mut str = &mut " hello ";
-   |                             ^^^^^^^^^^^^^^
+   |                             ^^^^^^^^^^^^^^ this mutable borrow refers to such a temporary
+   |
+   = note: Temporaries in constants and statics can have their lifetime extended until the end of the program
+   = note: To avoid accidentally creating global mutable state, such temporaries must be immutable
+   = help: If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
 error: aborting due to 1 previous error
 

tests/ui/consts/const-mut-refs/mut_ref_in_final.rs

@@ -12,13 +12,13 @@ const A: *const i32 = &4;
 // It could be made sound to allow it to compile,
 // but we do not want to allow this to compile,
 // as that would be an enormous footgun in oli-obk's opinion.
-const B: *mut i32 = &mut 4; //~ ERROR mutable borrows of lifetime-extended temporaries
+const B: *mut i32 = &mut 4; //~ ERROR mutable borrows of temporaries
 
 // Ok, no actual mutable allocation exists
 const B2: Option<&mut i32> = None;
 
 // Not ok, can't prove that no mutable allocation ends up in final value
-const B3: Option<&mut i32> = Some(&mut 42); //~ ERROR mutable borrows of lifetime-extended temporaries
+const B3: Option<&mut i32> = Some(&mut 42); //~ ERROR mutable borrows of temporaries
 
 const fn helper(x: &mut i32) -> Option<&mut i32> { Some(x) }
 const B4: Option<&mut i32> = helper(&mut 42); //~ ERROR temporary value dropped while borrowed
@@ -69,13 +69,13 @@ unsafe impl<T> Sync for SyncPtr<T> {}
 // (This relies on `SyncPtr` being a curly brace struct.)
 // However, we intern the inner memory as read-only, so this must be rejected.
 static RAW_MUT_CAST_S: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
-//~^ ERROR mutable borrows of lifetime-extended temporaries
+//~^ ERROR mutable borrows of temporaries
 static RAW_MUT_COERCE_S: SyncPtr<i32> = SyncPtr { x: &mut 0 };
-//~^ ERROR mutable borrows of lifetime-extended temporaries
+//~^ ERROR mutable borrows of temporaries
 const RAW_MUT_CAST_C: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
-//~^ ERROR mutable borrows of lifetime-extended temporaries
+//~^ ERROR mutable borrows of temporaries
 const RAW_MUT_COERCE_C: SyncPtr<i32> = SyncPtr { x: &mut 0 };
-//~^ ERROR mutable borrows of lifetime-extended temporaries
+//~^ ERROR mutable borrows of temporaries
 
 fn main() {
     println!("{}", unsafe { *A });

tests/ui/consts/const-mut-refs/mut_ref_in_final.stderr

@@ -1,14 +1,22 @@
-error[E0764]: mutable borrows of lifetime-extended temporaries in the top-level scope of a constant are not allowed
+error[E0764]: mutable borrows of temporaries that have their lifetime extended until the end of the program are not allowed
   --> $DIR/mut_ref_in_final.rs:15:21
    |
 LL | const B: *mut i32 = &mut 4;
-   |                     ^^^^^^
+   |                     ^^^^^^ this mutable borrow refers to such a temporary
+   |
+   = note: Temporaries in constants and statics can have their lifetime extended until the end of the program
+   = note: To avoid accidentally creating global mutable state, such temporaries must be immutable
+   = help: If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
-error[E0764]: mutable borrows of lifetime-extended temporaries in the top-level scope of a constant are not allowed
+error[E0764]: mutable borrows of temporaries that have their lifetime extended until the end of the program are not allowed
   --> $DIR/mut_ref_in_final.rs:21:35
    |
 LL | const B3: Option<&mut i32> = Some(&mut 42);
-   |                                   ^^^^^^^
+   |                                   ^^^^^^^ this mutable borrow refers to such a temporary
+   |
+   = note: Temporaries in constants and statics can have their lifetime extended until the end of the program
+   = note: To avoid accidentally creating global mutable state, such temporaries must be immutable
+   = help: If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
 error[E0716]: temporary value dropped while borrowed
   --> $DIR/mut_ref_in_final.rs:24:42
@@ -72,29 +80,45 @@ LL | static mut FOO3: NotAMutex<&mut i32> = NotAMutex(UnsafeCell::new(&mut 42));
    |                                        |                              creates a temporary value which is freed while still in use
    |                                        using this value as a static requires that borrow lasts for `'static`
 
-error[E0764]: mutable borrows of lifetime-extended temporaries in the top-level scope of a static are not allowed
+error[E0764]: mutable borrows of temporaries that have their lifetime extended until the end of the program are not allowed
   --> $DIR/mut_ref_in_final.rs:71:53
    |
 LL | static RAW_MUT_CAST_S: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
-   |                                                     ^^^^^^^
+   |                                                     ^^^^^^^ this mutable borrow refers to such a temporary
+   |
+   = note: Temporaries in constants and statics can have their lifetime extended until the end of the program
+   = note: To avoid accidentally creating global mutable state, such temporaries must be immutable
+   = help: If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
-error[E0764]: mutable borrows of lifetime-extended temporaries in the top-level scope of a static are not allowed
+error[E0764]: mutable borrows of temporaries that have their lifetime extended until the end of the program are not allowed
   --> $DIR/mut_ref_in_final.rs:73:54
    |
 LL | static RAW_MUT_COERCE_S: SyncPtr<i32> = SyncPtr { x: &mut 0 };
-   |                                                      ^^^^^^
+   |                                                      ^^^^^^ this mutable borrow refers to such a temporary
+   |
+   = note: Temporaries in constants and statics can have their lifetime extended until the end of the program
+   = note: To avoid accidentally creating global mutable state, such temporaries must be immutable
+   = help: If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
-error[E0764]: mutable borrows of lifetime-extended temporaries in the top-level scope of a constant are not allowed
+error[E0764]: mutable borrows of temporaries that have their lifetime extended until the end of the program are not allowed
   --> $DIR/mut_ref_in_final.rs:75:52
    |
 LL | const RAW_MUT_CAST_C: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
-   |                                                    ^^^^^^^
+   |                                                    ^^^^^^^ this mutable borrow refers to such a temporary
+   |
+   = note: Temporaries in constants and statics can have their lifetime extended until the end of the program
+   = note: To avoid accidentally creating global mutable state, such temporaries must be immutable
+   = help: If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
-error[E0764]: mutable borrows of lifetime-extended temporaries in the top-level scope of a constant are not allowed
+error[E0764]: mutable borrows of temporaries that have their lifetime extended until the end of the program are not allowed
   --> $DIR/mut_ref_in_final.rs:77:53
    |
 LL | const RAW_MUT_COERCE_C: SyncPtr<i32> = SyncPtr { x: &mut 0 };
-   |                                                     ^^^^^^
+   |                                                     ^^^^^^ this mutable borrow refers to such a temporary
+   |
+   = note: Temporaries in constants and statics can have their lifetime extended until the end of the program
+   = note: To avoid accidentally creating global mutable state, such temporaries must be immutable
+   = help: If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
 error: aborting due to 12 previous errors
 

tests/ui/consts/const-promoted-opaque.atomic.stderr

@@ -7,11 +7,15 @@ LL |
 LL | };
    | - value is dropped here
 
-error[E0492]: interior mutable shared borrows of lifetime-extended temporaries in the top-level scope of a constant are not allowed
+error[E0492]: interior mutable shared borrows of temporaries that have their lifetime extended until the end of the program are not allowed
   --> $DIR/const-promoted-opaque.rs:36:19
    |
 LL | const BAZ: &Foo = &FOO;
-   |                   ^^^^ this borrow of an interior mutable value refers to a lifetime-extended temporary
+   |                   ^^^^ this borrow of an interior mutable value refers to such a temporary
+   |
+   = note: Temporaries in constants and statics can have their lifetime extended until the end of the program
+   = note: To avoid accidentally creating global mutable state, such temporaries must be immutable
+   = help: If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
 error[E0716]: temporary value dropped while borrowed
   --> $DIR/const-promoted-opaque.rs:40:26

tests/ui/consts/const-promoted-opaque.rs

@@ -34,7 +34,7 @@ const BAR: () = {
 };
 
 const BAZ: &Foo = &FOO;
-//[atomic]~^ ERROR: interior mutable shared borrows of lifetime-extended temporaries
+//[atomic]~^ ERROR: interior mutable shared borrows of temporaries
 
 fn main() {
     let _: &'static _ = &FOO;

tests/ui/consts/issue-17718-const-bad-values.rs

@@ -5,7 +5,7 @@
 #![allow(static_mut_refs)]
 
 const C1: &'static mut [usize] = &mut [];
-//~^ ERROR: mutable borrows of lifetime-extended temporaries
+//~^ ERROR: mutable borrows of temporaries
 
 static mut S: i32 = 3;
 const C2: &'static mut i32 = unsafe { &mut S };

tests/ui/consts/issue-17718-const-bad-values.stderr

@@ -1,8 +1,12 @@
-error[E0764]: mutable borrows of lifetime-extended temporaries in the top-level scope of a constant are not allowed
+error[E0764]: mutable borrows of temporaries that have their lifetime extended until the end of the program are not allowed
   --> $DIR/issue-17718-const-bad-values.rs:7:34
    |
 LL | const C1: &'static mut [usize] = &mut [];
-   |                                  ^^^^^^^
+   |                                  ^^^^^^^ this mutable borrow refers to such a temporary
+   |
+   = note: Temporaries in constants and statics can have their lifetime extended until the end of the program
+   = note: To avoid accidentally creating global mutable state, such temporaries must be immutable
+   = help: If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
 error[E0080]: constructing invalid value: encountered mutable reference in `const` value
   --> $DIR/issue-17718-const-bad-values.rs:11:1

tests/ui/consts/issue-17718-const-borrow.rs

@@ -2,13 +2,13 @@ use std::cell::UnsafeCell;
 
 const A: UnsafeCell<usize> = UnsafeCell::new(1);
 const B: &'static UnsafeCell<usize> = &A;
-//~^ ERROR: interior mutable shared borrows of lifetime-extended temporaries
+//~^ ERROR: interior mutable shared borrows of temporaries
 
 struct C { a: UnsafeCell<usize> }
 const D: C = C { a: UnsafeCell::new(1) };
 const E: &'static UnsafeCell<usize> = &D.a;
-//~^ ERROR: interior mutable shared borrows of lifetime-extended temporaries
+//~^ ERROR: interior mutable shared borrows of temporaries
 const F: &'static C = &D;
-//~^ ERROR: interior mutable shared borrows of lifetime-extended temporaries
+//~^ ERROR: interior mutable shared borrows of temporaries
 
 fn main() {}

tests/ui/consts/issue-17718-const-borrow.stderr

@@ -1,20 +1,32 @@
-error[E0492]: interior mutable shared borrows of lifetime-extended temporaries in the top-level scope of a constant are not allowed
+error[E0492]: interior mutable shared borrows of temporaries that have their lifetime extended until the end of the program are not allowed
   --> $DIR/issue-17718-const-borrow.rs:4:39
    |
 LL | const B: &'static UnsafeCell<usize> = &A;
-   |                                       ^^ this borrow of an interior mutable value refers to a lifetime-extended temporary
+   |                                       ^^ this borrow of an interior mutable value refers to such a temporary
+   |
+   = note: Temporaries in constants and statics can have their lifetime extended until the end of the program
+   = note: To avoid accidentally creating global mutable state, such temporaries must be immutable
+   = help: If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
-error[E0492]: interior mutable shared borrows of lifetime-extended temporaries in the top-level scope of a constant are not allowed
+error[E0492]: interior mutable shared borrows of temporaries that have their lifetime extended until the end of the program are not allowed
   --> $DIR/issue-17718-const-borrow.rs:9:39
    |
 LL | const E: &'static UnsafeCell<usize> = &D.a;
-   |                                       ^^^^ this borrow of an interior mutable value refers to a lifetime-extended temporary
+   |                                       ^^^^ this borrow of an interior mutable value refers to such a temporary
+   |
+   = note: Temporaries in constants and statics can have their lifetime extended until the end of the program
+   = note: To avoid accidentally creating global mutable state, such temporaries must be immutable
+   = help: If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
-error[E0492]: interior mutable shared borrows of lifetime-extended temporaries in the top-level scope of a constant are not allowed
+error[E0492]: interior mutable shared borrows of temporaries that have their lifetime extended until the end of the program are not allowed
   --> $DIR/issue-17718-const-borrow.rs:11:23
    |
 LL | const F: &'static C = &D;
-   |                       ^^ this borrow of an interior mutable value refers to a lifetime-extended temporary
+   |                       ^^ this borrow of an interior mutable value refers to such a temporary
+   |
+   = note: Temporaries in constants and statics can have their lifetime extended until the end of the program
+   = note: To avoid accidentally creating global mutable state, such temporaries must be immutable
+   = help: If you really want global mutable state, try replacing the temporary by an interior mutable `static` or a `static mut`
 
 error: aborting due to 3 previous errors
 

tests/ui/consts/partial_qualif.rs

@@ -3,7 +3,7 @@ use std::cell::Cell;
 const FOO: &(Cell<usize>, bool) = {
     let mut a = (Cell::new(0), false);
     a.1 = true; // sets `qualif(a)` to `qualif(a) | qualif(true)`
-    &{a} //~ ERROR interior mutable shared borrows of lifetime-extended temporaries
+    &{a} //~ ERROR interior mutable shared borrows of temporaries
 };
 
 fn main() {}