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Allow parsing foreign impl blocks #102376

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@maurer maurer commented Sep 27, 2022

Allow parsing foreign impl blocks for use by proc macros.

This allows more ergonomic description of methods and associated functions both when describing rust types to be exported and when importing class-like objects from other languages.

My primary motivation for this change is clean support for C++ static methods - this could be done with alternate syntax (e.g. explicit attributes to associate these functions with classes), but this seems much cleaner and potentially useful for interfacing with other languages beyond C++.

The Rust language itself remains unmodified - foreign impl blocks which make it past the macro expansion stage will not compile, and additional tests have been added to ensure this remains the case.

#75857 is prior art on this kind of change, but is substantially less involved.

cc @dtolnay

@rustbot rustbot added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-rustdoc Relevant to the rustdoc team, which will review and decide on the PR/issue. labels Sep 27, 2022
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r? @nagisa

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 27, 2022
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rustbot commented Sep 27, 2022

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

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Allow `impl` blocks in foreign modules for more ergonomic use in macros.
`impl` blocks still have no meaning in foreign modules and will cause an
error if still present during lowering.

Also adds explicit tests for the previous similar foreign module macro
extensions to ensure that neither this nor those are accepted or crash
the compiler when *not* fed to a macro.
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est31 commented Sep 28, 2022

I'm not sure they'll accept this, given that #78849 was rejected. Maybe one could generally make parsing weaker for attr proc macros: #78849 (comment)

Edit: obviously good C++ compatibility is more important than postfix macros, but the general argument of not adding even more exceptions to the tokens, and this seems to be a big exception, still exists.

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nagisa commented Sep 28, 2022

cc @petrochenkov

I’m thinking that this probably wants an compiler team MCP with all the votes and such before this can land.

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bors commented Sep 29, 2022

☔ The latest upstream changes (presumably #102461) made this pull request unmergeable. Please resolve the merge conflicts.

@nagisa nagisa added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 28, 2022
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@maurer
Ping from triage: I'm closing this due to inactivity, Please reopen when you are ready to continue with this.
Note: if you do please open the PR BEFORE you push to it, else you won't be able to reopen - this is a quirk of github.
Thanks for your contribution.

@rustbot label: +S-inactive

@JohnCSimon JohnCSimon closed this Jan 1, 2023
@rustbot rustbot added the S-inactive Status: Inactive and waiting on the author. This is often applied to closed PRs. label Jan 1, 2023
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8 participants