Ralf Jung 7ee19eb038 Rollup merge of #154475 - fmease:soft-gate-box-struct-field-pat, r=Kivooeo ...

Emit a pre-expansion feature gate warning for `box`'ed struct field patterns

While the following code triggers a feature gate *warning*:

```rs
fn f() {
    #[cfg(false)]
    let box x; //~ WARN box pattern syntax is experimental
}
```

the code below does not (on stable & main):

```rs
fn f() {
    #[cfg(false)]
    let Struct { box x };
}
```

This is an oversight as both are part of the unstable feature `box_patterns` (that isn't properly gated pre expansion for historical reasons). Of course, both forms lead to a feature gate error *post expansion*.

This is a bug fix and doesn't need any input from T-compiler or T-lang. For context, emitting warnings in these cases is legitimized by [MCP 535](https://github.com/rust-lang/compiler-team/issues/535)[^1].

Part of rust-lang/rust#154045.

[^1]: In case you're wondering why the MCP talks about a *lint* even though the feature gate warnings as seen today don't reference any lint by name, read https://github.com/rust-lang/rust/issues/154045#issuecomment-4144034419.

2026-03-28 13:15:53 +01:00

..

src

Rollup merge of #154475 - fmease:soft-gate-box-struct-field-pat, r=Kivooeo

2026-03-28 13:15:53 +01:00

Cargo.toml

Convert to inline diagnostics in rustc_parse

2026-02-07 10:30:40 +01:00