report call site of inlined scopes for large assignment lints

[jogru0]

Addressed issue: #121672
Tracking issue: #83518

r? @oli-obk

I tried to follow your comment about what to do here. However, I'm totally unfamiliar with the code so far (this is my first contribution touching compiler code), so I apologize in advance if I did something stupid 😅

In particular, I'm not sure I use the correct source scope to look for inline data, as there is a whole IndexVec of them. My changes definitely did something, as can be seen by the added ui test. However, the result is not as anticipated in the issue:

LL |     let cell = std::cell::UnsafeCell::new(data);
   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ value moved from here

instead of

LL |     let cell = std::cell::UnsafeCell::new(data);
   |                                           ^^^^ value moved from here

raising my suspicion that maybe I got the wrong source scope.

[oli-obk]

Hmm, you could try just returning early if inlined is Some. I think then you should get the improved span that you were looking for. The call site span points to the entire function call indeed, and will result in exactly what you showed. But I'm not sure the more detailed span of the argument still exists

[jogru0]

If I do this early return, I don't get any lint at all:

failures:

---- [ui] tests/ui/lint/large_assignments/inline_mir.rs stdout ----

error: ui test did not emit an error
note: by default, ui tests are expected not to compile
status: exit status: 0

[oli-obk]

hmm our docs are very underwhelming on this. Maybe use the source_scope_data.span if inlined is set?

[jogru0]

In the ui test example, span points to

UnsafeCell { value }

and source_scope_data.span points to

pub const fn new(value: T) -> UnsafeCell<T> {
    UnsafeCell { value }
}

so both seem to be wrong to me.

By the way, both currently don't show up in the actual stderr output, contrary to how it was reported in the issue originally. They both look like this:

error: moving 9999 bytes
  --> $SRC_DIR/core/src/cell.rs:LL:COL
  ::: $SRC_DIR/core/src/cell.rs:LL:COL
   |
   = note: value moved from here
   |
   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
note: the lint level is defined here
  --> $DIR/inline_mir.rs:2:9
   |
LL | #![deny(large_assignments)]
   |         ^^^^^^^^^^^^^^^^^

error: aborting due to 1 previous error

[oli-obk]

hmm... I guess we lose the argument span entirely in favor of spans from the inlined item. That may be something we may want to adjust, but not in this PR. I'd say we land it with the caller span

[oli-obk]

Thanks for the analyses of the alternatives!

@bors r+ rollup

[bors]

📌 Commit 6d71fc1 has been approved by oli-obk

It is now in the queue for this repository.