$crate incorrectly substituted in attribute macro invocation containing bang macro invocation · Issue #62325 · rust-lang/rust (original) (raw)

When an attribute macro input contains $ident, it is correctly substituted both inside and outside of a function-like macro invocation i.e. both of the ident′sin‘[u8;ident's in [u8; </annotation></semantics></math>ident′sin‘[u8;ident + m!($ident)] would be substituted as expected.

But when an attribute macro input contains $crate, it is only substituted outside of a function-like macro. Inside, it incorrectly disintegrates into Punct('$'), Ident(crate) when the whole bang macro invocation is passed to an attribute macro (or derive macro). In the case of [u8; <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>c</mi><mi>r</mi><mi>a</mi><mi>t</mi><mi>e</mi><mo>:</mo><mo>:</mo><mi>N</mi><mo>+</mo><mi>m</mi><mo stretchy="false">!</mo><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">crate::N + m!(</annotation></semantics></math>crate::N+m!(crate::N)] the first $crate would be handled correctly but the second one would be passed incorrectly as two tokens. See where I put // WRONG in the output below.

TokenStream [ Ident { ident: "type", span: #0 bytes(0..0), }, Ident { ident: "T", span: #0 bytes(0..0), }, Punct { ch: '=', spacing: Alone, span: #0 bytes(0..0), }, Group { delimiter: Bracket, stream: TokenStream [ Ident { ident: "crate", span: #0 bytes(0..0), }, Punct { ch: ':', spacing: Joint, span: #0 bytes(0..0), }, Punct { ch: ':', spacing: Alone, span: #0 bytes(0..0), }, Ident { ident: "N", span: #0 bytes(0..0), }, Punct { ch: ';', spacing: Alone, span: #0 bytes(0..0), }, Ident { ident: "x", span: #0 bytes(0..0), }, Punct { ch: '!', spacing: Alone, span: #0 bytes(0..0), }, Group { delimiter: Parenthesis, stream: TokenStream [ Punct { // WRONG ch: '$', spacing: Alone, span: #0 bytes(0..0), }, Ident { ident: "crate", span: #0 bytes(0..0), }, Punct { ch: ':', spacing: Joint, span: #0 bytes(0..0), }, Punct { ch: ':', spacing: Alone, span: #0 bytes(0..0), }, Ident { ident: "N", span: #0 bytes(0..0), }, ], span: #0 bytes(0..0), }, ], span: #0 bytes(0..0), }, Punct { ch: ';', spacing: Alone, span: #0 bytes(0..0), }, ]