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Explaining things that took me some time to work out.
This commit is contained in:
Nicholas Nethercote 2024-07-10 16:29:48 +10:00
parent d6ebbbfcb2
commit 478ba59026
2 changed files with 7 additions and 1 deletions
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5
compiler/rustc_ast/src/tokenstream.rs
View File

@ -269,11 +269,14 @@ fn attrs_and_tokens_to_token_trees(
/// with its attributes.
///
/// This is constructed during parsing when we need to capture
/// tokens.
/// tokens, for `cfg` and `cfg_attr` attributes.
///
/// For example, `#[cfg(FALSE)] struct Foo {}` would
/// have an `attrs` field containing the `#[cfg(FALSE)]` attr,
/// and a `tokens` field storing the (unparsed) tokens `struct Foo {}`
///
/// The `cfg`/`cfg_attr` processing occurs in
/// `StripUnconfigured::configure_tokens`.
#[derive(Clone, Debug, Encodable, Decodable)]
pub struct AttrsTarget {
/// Attributes, both outer and inner.

3
compiler/rustc_expand/src/config.rs
View File

@ -187,6 +187,7 @@ impl<'a> StripUnconfigured<'a> {
.iter()
.filter_map(|tree| match tree.clone() {
AttrTokenTree::AttrsTarget(mut target) => {
// Expand any `cfg_attr` attributes.
target.attrs.flat_map_in_place(|attr| self.process_cfg_attr(&attr));
if self.in_cfg(&target.attrs) {
@ -195,6 +196,8 @@ impl<'a> StripUnconfigured<'a> {
);
Some(AttrTokenTree::AttrsTarget(target))
} else {
// Remove the target if there's a `cfg` attribute and
// the condition isn't satisfied.
None
}
}