Enum SyntheticAttr 

pub enum SyntheticAttr {
    CfgTrace(CfgEntry),
    CfgAttrTrace,
}

Synthetic attributes are inserted by the compiler. They cannot be written in source code, and so cannot be pretty-printed by the AST pretty printer (because its output should be valid Rust code). They receive special treatment because they must not affect observable language behaviour: they are invisible to proc macros and are unable to re-enter the parser.

Variants

CfgTrace(CfgEntry)

This synthetic attribute is added by the compiler when a cfg attribute is expanded so that subsequent code can tell that conditional compilation occurred. A #[cfg(pred)] with a true predicate is replaced by a synthetic CfgTrace attribute that records the parsed predicate. A #[cfg(pred)] with a false predicate leaves no trace because there is no node left to annotate.

The attribute is used for some diagnostics, by rustdoc (for detecting feature usage), and by some clippy lints.

CfgAttrTrace

This synthetic attribute is added by the compiler when a cfg_attr attribute is expanded so that subsequent code can tell that conditional compilation occurred. A #[cfg_attr(pred, attrs)] is replaced by a synthetic CfgAttrTrace attribute whether the predicate evaluated true or not (or even failed to parse). The pred and attrs are not recorded because they are not needed.

The attribute is used by some clippy lints.

Trait Implementations

impl Clone for SyntheticAttr

fn clone(&self) -> SyntheticAttr

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for SyntheticAttr

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<__D: SpanDecoder> Decodable<__D> for SyntheticAttr

fn decode(__decoder: &mut __D) -> Self

impl<__E: SpanEncoder> Encodable<__E> for SyntheticAttr

fn encode(&self, __encoder: &mut __E)

impl<V: MutVisitor> MutVisitable<V> for SyntheticAttr

type Extra = ()

fn visit_mut(&mut self, _vis: &mut V, _extra: Self::Extra) -> V::Result

impl StableHash for SyntheticAttr

fn stable_hash<__Hcx: StableHashCtxt>( &self, __hcx: &mut __Hcx, __hasher: &mut StableHasher, )

impl<'a, V: Visitor<'a>> Visitable<'a, V> for SyntheticAttr

type Extra = ()

fn visit(&'a self, _vis: &mut V, _extra: Self::Extra) -> V::Result

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 24 bytes

Size for each variant:

• CfgTrace: 24 bytes
• CfgAttrTrace: 0 bytes