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Rollup merge of #100507 - cameron1024:suggest-lazy, r=compiler-errors

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suggest `once_cell::Lazy` for non-const statics

Addresses https://github.com/rust-lang/rust/issues/100410

Some questions:
 - removing the `if` seems to include too many cases (e.g. calls to non-const functions inside a `const fn`), but this code excludes the following case:
```rust
const FOO: Foo = non_const_fn();
```
Should we suggest `once_cell` in this case as well?
 - The original issue mentions suggesting `AtomicI32` instead of `Mutex<i32>`, should this PR address that as well?
This commit is contained in:
Matthias Krüger 2022-08-20 07:08:59 +02:00 • committed by GitHub
commit c4b83ebe7c
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5
compiler/rustc_const_eval/src/transform/check_consts/ops.rs
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@ -1,6 +1,7 @@
//! Concrete error types for all operations which may be invalid in a certain const context.
use hir::def_id::LocalDefId;
use hir::ConstContext;
use rustc_errors::{
error_code, struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed,
};
@ -331,6 +332,10 @@ impl<'tcx> NonConstOp<'tcx> for FnCallNonConst<'tcx> {
ccx.const_kind(),
));
if let ConstContext::Static(_) = ccx.const_kind() {
err.note("consider wrapping this expression in `Lazy::new(|| ...)` from the `once_cell` crate: https://crates.io/crates/once_cell");
}
err
}
}