This commit introduces a check to ensure that the lint won't trigger when the initializer is
unreachable, such as:
```
thread_local! {
static STATE: Cell<usize> = panic!();
}
```
This is achieved by looking at the unpeeled initializer expression and ensuring that the parent
macro is not `panic!()`, `todo!()`, `unreachable!()`, `unimplemented!()`.
fixes#12637
changelog: [`threadlocal_initializer_can_be_made_const`] will no longer trigger on `unreachable` macros.
`os_local` impl of `thread_local` — regardless of whether it is const and
unlike other implementations — includes an `fn __init(): EXPR`.
Existing implementation of the lint checked for the presence of said
function and whether the expr can be made const. Because for `os_local`
we always have an `__init()`, it triggers for const implementations.
The solution is to check whether the `__init()` function is already const.
If it is `const`, there is nothing to do. Otherwise, we verify that we can
make it const.
Co-authored-by: Alejandra González <blyxyas@gmail.com>
Adds a new lint to suggest using `const` on `thread_local!`
initializers that can be evaluated at compile time.
Impl details:
The lint relies on the expansion of `thread_local!`. For non
const-labelled initializers, `thread_local!` produces a function
called `__init` that lazily initializes the value. We check the function
and decide whether the body can be const. The body of the function is
exactly the initializer. If so, we lint the body.
changelog: new lint [`thread_local_initializer_can_be_made_const`]
