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Jonathan Brouwer
4486e4f235
fix(codegen): Use `body_codegen_attrs` For Caller In `adjust_target_feature_sig`
### Summary:
#### Problem:
Coercing a `#[target_feature]` `const fn` to a function pointer inside a `const` body triggers an ICE (debug builds only):
```rust
#[target_feature(enable = "sse2")]
const fn with_target_feature() {}
const X: () = unsafe {
let _: unsafe fn() = with_target_feature; // ICE
};
```
```text
assertion failed: def_kind.has_codegen_attrs()
unexpected `def_kind` in `codegen_fn_attrs`: Const
```
#### Root Cause:
Introduced in rust-lang/rust#135504 (2025-01-14, commit `8fee6a77394`). `adjust_target_feature_sig` unconditionally calls `codegen_fn_attrs(caller)` to get the caller's target features. `codegen_fn_attrs` requires that the `DefId` satisfies `has_codegen_attrs()`. `DefKind::Const`, `AssocConst`, and `InlineConst` do not — they have no codegen attributes by design. The debug assertion fires.
In release builds the call "worked" accidentally: `codegen_fn_attrs` on a const would reach the query machinery and happen to return empty attributes, producing a correct (but unguaranteed) result. The bug was latent until debug builds exposed it.
#### Solution:
Replace `codegen_fn_attrs(caller)` with `body_codegen_attrs(caller)`. `body_codegen_attrs` exists precisely for this case: it delegates to `codegen_fn_attrs` for function-like `DefKind`s and returns `CodegenFnAttrs::EMPTY` for const items. A const body has no target features, so returning empty is semantically correct.
Also fix the pre-existing variable name `callee_features` → `caller_features` (the variable holds the *caller*'s features, not the callee's).
### Changes:
- `compiler/rustc_middle/src/ty/context.rs`: `adjust_target_feature_sig` — use `body_codegen_attrs` for `caller`; rename `callee_features` → `caller_features`.
- `tests/ui/target-feature/const-target-feature-fn-ptr-coercion.rs`: regression test covering `Const`, `AssocConst`, and `InlineConst` caller contexts.
Fixes rust-lang/rust#152340.