Improve error[E0492]: statics cannot refer to interior mutable data

[Sunshine40]

Code

static STATIC_REF: &AtomicIsize = &AtomicIsize::new(0);

Current output

error[E0492]: statics cannot refer to interior mutable data
 --> src/lib.rs:3:35
  |
3 | static STATIC_REF: &AtomicIsize = &AtomicIsize::new(0);
  |                                   ^^^^^^^^^^^^^^^^^^^^ this borrow of an interior mutable value may end up in the final value
  |
  = help: to fix this, the value can be extracted to a separate `static` item and then referenced

Desired output

error[E0492]: statics cannot refer to anonymous interior mutable data
 --> src/lib.rs:3:35
  |
3 | static STATIC_REF: &AtomicIsize = &AtomicIsize::new(0);
  |                                   ^^^^^^^^^^^^^^^^^^^^ this borrow of an interior mutable value may end up in the final value
  |
  = help: to fix this, the value can be extracted to a separate `static` item and then referenced

Rationale and extra context

more discussion here: https://users.rust-lang.org/t/why-compiler-error-e0492-statics-cannot-refer-to-interior-mutable-data/110266

Other cases

No response

Rust Version

rustc 1.77.2 (25ef9e3d8 2024-04-09)
binary: rustc
commit-hash: 25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04
commit-date: 2024-04-09
host: x86_64-pc-windows-msvc
release: 1.77.2
LLVM version: 17.0.6

Anything else?

No response

[steffahn]

I don't think "anonymous" adds much clarity at all. The main problem I see is that the general message that "statics cannot refer to interior mutable data" is just plain wrong, and "anonymous" doesn't fix it.

Thinking of other suboptimal alternatives, "constant initializer expressions for statics cannot refer to interior mutable data" would be wrong, too; other statics containing interior mutable data can be referenced in those.

Constant static promotion is not relevant here, either, because with interior mutability it doesn't happen in the first place.

I'd guess, this really is about lifetime extended temporaries in static initializers (the ordinary lifetime extension, not the similar term in the context of 'const promotion').

Maybe a short message could thus be something like

statics initializers cannot refer to interior mutable data outside of static items

and the help texts or notes could call out the value that is subject to lifetime extension; with this error message and note/help text as context, the suggestion to move that into a separate static is then also very unsurprising IMO.

[chenyukang]

now the output adds more information:

error[E0492]: interior mutable shared borrows of temporaries that have their lifetime extended until the end of the program are not allowed
  --> $DIR/static-temporary-borrow-diagnostic-issue-124232.rs:10:38
   |
LL | static TEMPORARY_REF: &AtomicIsize = &AtomicIsize::new(0);
   |                                      ^^^^^^^^^^^^^^^^^^^^ 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 1 previous error

For more information about this error, try `rustc --explain E0492`.

link #140942