Rework treatment of $crate in procedural macros
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@bors: r+ This sounds like a solid strategy to me, thanks @petrochenkov! |
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This PR might have failed #56873 (comment); might possibly also have been due to being combined with #56737. |
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Rework treatment of `$crate` in procedural macros Important clarification: `$crate` below means "processed `$crate`" or "output `$crate`". In the input of a decl macro `$crate` is just two separate tokens, but in the *output of a decl macro* `$crate` is a single keyword identifier (#55640 (comment)). First of all, this PR removes the `eliminate_crate_var` hack. `$crate::foo` is no longer replaced with `::foo` or `::crate_name::foo` in the input of derive proc macros, it's passed to the macro instead with its precise span and hygiene data, and can be treated as any other path segment keyword (like `crate` or `self`) after that. (Note: `eliminate_crate_var` was never used for non-derive proc macros.) This creates an annoying problem - derive macros still may stringify their input before processing and expect `$crate` survive that stringification and refer to the same crate (the Rust 1.15-1.29 way of doing things). Moreover, the input of proc macro attributes and derives (but not fn-like proc macros) also effectively survives stringification before being passed to the macro (also for legacy implementation reasons). So we kind of resurrect the `eliminate_crate_var` hack in reduced form, but apply it only to AST pretty-printing. If an AST fragment is pretty-printed, the resulting *text* will have `$crate` replaced with `crate` or `::crate_name`. This should be enough to keep all the legacy cases working. Closes #55640 Closes #56622 r? @ghost
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…ulacrum Fix pretty-printing of `$crate` (take 4) Pretty-print `$crate` as `crate` or `crate_name` in unstructured tokens like `a $crate c` in `foo!(a $crate c)`, but only if those tokens are printed as a part of AST pretty-printing, rather than as a standalone token stream. Fixes rust-lang#62325 Previous iterations - rust-lang#56647, rust-lang#57155, rust-lang#57915.
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Important clarification:
$cratebelow means "processed$crate" or "output$crate". In the input of a decl macro$crateis just two separate tokens, but in the output of a decl macro$crateis a single keyword identifier (#55640 (comment)).First of all, this PR removes the
eliminate_crate_varhack.$crate::foois no longer replaced with::fooor::crate_name::fooin the input of derive proc macros, it's passed to the macro instead with its precise span and hygiene data, and can be treated as any other path segment keyword (likecrateorself) after that. (Note:eliminate_crate_varwas never used for non-derive proc macros.)This creates an annoying problem - derive macros still may stringify their input before processing and expect
$cratesurvive that stringification and refer to the same crate (the Rust 1.15-1.29 way of doing things).Moreover, the input of proc macro attributes and derives (but not fn-like proc macros) also effectively survives stringification before being passed to the macro (also for legacy implementation reasons).
So we kind of resurrect the
eliminate_crate_varhack in reduced form, but apply it only to AST pretty-printing.If an AST fragment is pretty-printed, the resulting text will have
$cratereplaced withcrateor::crate_name. This should be enough to keep all the legacy cases working.Closes #55640
Closes #56622
r? @ghost