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Rollup merge of #138844 - petrochenkov:cfgtrace2, r=nnethercote

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expand: Leave traces when expanding `cfg` attributes

This is the same as https://github.com/rust-lang/rust/pull/138515, but for `cfg(true)` instead of `cfg_attr`.

The difference is that `cfg(true)`s already left "traces" after themselves - the `cfg` attributes themselves, with `expanded_inert_attrs` set to true, with full tokens, available to proc macros.
This is not a reasonably expected behavior, but it could not be removed without a replacement, because a [major rustdoc feature](https://github.com/rust-lang/rfcs/pull/3631) and a number of clippy lints rely on it. This PR implements a replacement.

This needs a crater run, because it changes observable behavior (in an intended way) - proc macros can no longer see expanded `cfg(true)` attributes.

(Some minor unnecessary special casing for `sym::cfg_attr` is also removed in this PR.)

r? `@nnethercote`
This commit is contained in:
Jacob Pratt 2025-03-27 13:11:17 -04:00 • committed by GitHub
commit 3a8621d681
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24 changed files with 88 additions and 108 deletions
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9
compiler/rustc_parse/src/validate_attr.rs
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@ -16,7 +16,8 @@ use rustc_span::{Span, Symbol, sym};
use crate::{errors, parse_in};
pub fn check_attr(psess: &ParseSess, attr: &Attribute) {
if attr.is_doc_comment() || attr.has_name(sym::cfg_attr_trace) {
if attr.is_doc_comment() || attr.has_name(sym::cfg_trace) || attr.has_name(sym::cfg_attr_trace)
{
return;
}
@ -215,11 +216,7 @@ pub fn check_builtin_meta_item(
template: AttributeTemplate,
deny_unsafety: bool,
) {
// Some special attributes like `cfg` must be checked
// before the generic check, so we skip them here.
let should_skip = |name| name == sym::cfg;
if !should_skip(name) && !is_attr_template_compatible(&template, &meta.kind) {
if !is_attr_template_compatible(&template, &meta.kind) {
emit_malformed_attribute(psess, style, meta.span, name, template);
}