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

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`

1 files changed, 3 insertions, 6 deletions

diff --git a/compiler/rustc_parse/src/validate_attr.rs b/compiler/rustc_parse/src/validate_attr.rs
index 9ecde2a9eb5..6bbd650dcdf 100644
--- a/compiler/rustc_parse/src/validate_attr.rs
+++ b/compiler/rustc_parse/src/validate_attr.rs
@@ -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);
     }