In which we start to parse const generics defaults #80547

lqd · 2020-12-31T02:03:17Z

As discussed in this zulip topic, this PR extracts the parsing parts from @JulianKnodt's PR #75384 for a better user-experience using the newly stabilized min_const_generics (albeit temporary) as shown in #80507: trying to use default values on const generics currently results in parse errors, as if the user didn't use the correct syntax (which is somewhat true but also misleading).

This PR extracts (and slightly modifies in a couple places) @JulianKnodt's parsing code (with attribution if I've done everything correctly), AST and HIR changes, and feature gate setup.

This feature is now marked as "incomplete" and thus will also print out the expected "const generics default values are unstable" error instead of a syntax error. Note that, as I've only extracted the parsing part, the actual feature will not work at all if enabled. There will be ICEs, and inference errors on the const generics default values themselves.

Fixes #80507.

Once this merges, I'll:

modify the const generics tracking issue to refer to the const_generics_defaults gate rather than the older temporary name it uses there.
create the GH F-const_generics_defaults label

r? @varkor

varkor · 2020-12-31T02:44:58Z

Thanks @lqd — and thanks for the work on the parsing and lowering changes, @JulianKnodt!

@bors r+

bors · 2020-12-31T02:45:00Z

📌 Commit 583e7e4f13300946c88cf5393a585ec873cf38f9 has been approved by varkor

varkor · 2020-12-31T13:13:53Z

@bors r-

Something was brought something to my attention regarding accidental stabilisation of the syntax.

varkor · 2020-12-31T13:18:51Z

The issue I had overlooked is that we're feature gating too liberally here, in that the new syntax will not be forbidden under #[cfg(FALSE)], so that it's still accepted by the parser, even though it's supposed to be unstable syntax. The feature gating should take place in feature_gate.rs rather than ast_validation.rs: we need to collect the spans corresponding to the default generic parameters so that we can emit correct errors.

There's an example in this PR: https://github.com/rust-lang/rust/pull/63545/files

@lqd: sorry for overlooking this. Would you be able to make the changes and add a new test for #[cfg(FALSE)]?

lqd · 2020-12-31T14:58:17Z

@varkor sure !

varkor · 2020-12-31T17:41:29Z

Thanks!

@bors r+

bors · 2020-12-31T17:41:31Z

📌 Commit d02ac5a4bf01151b68e25ccc10d43293c4990cd6 has been approved by varkor

bors · 2020-12-31T18:19:19Z

☔ The latest upstream changes (presumably #80459) made this pull request unmergeable. Please resolve the merge conflicts.

lqd · 2020-12-31T20:02:35Z

@bors r=varkor

bors · 2020-12-31T20:02:37Z

📌 Commit 2a012649d6df03f1ea1ee078effe44842d79b29e has been approved by varkor

Rollup of 8 pull requests Successful merges: - rust-lang#80323 (Update and improve `rustc_codegen_{llvm,ssa}` docs) - rust-lang#80368 (rustdoc: Render visibilities succinctly) - rust-lang#80514 (Fix broken ./x.py install) - rust-lang#80519 (Take type defaults into account in suggestions to reorder generic parameters) - rust-lang#80526 (Update LLVM) - rust-lang#80532 (remove unnecessary trailing semicolon from bootstrap) - rust-lang#80548 (FIx ICE on wf check for foreign fns) - rust-lang#80551 (support pattern as const parents in type_of) Failed merges: - rust-lang#80547 (In which we start to parse const generics defaults) r? `@ghost` `@rustbot` modify labels: rollup

bors · 2021-01-01T04:15:15Z

☔ The latest upstream changes (presumably #80566) made this pull request unmergeable. Please resolve the merge conflicts.

- Adds optional default values to const generic parameters in the AST and HIR - Parses these optional default values - Adds a `const_generics_defaults` feature gate

The `const_generics_defaults` now handles them, and they correctly parse, so we can update these tests expecting a parser error .

This is important to not accidentally stabilize the parsing of the syntax while it still is experimental and not formally accepted

lqd · 2021-01-01T11:10:04Z

@bors r=varkor

bors · 2021-01-01T11:10:06Z

📌 Commit 942b7ce has been approved by varkor

bors · 2021-01-01T13:17:47Z

⌛ Testing commit 942b7ce with merge a609fb4...

bors · 2021-01-01T16:12:20Z

☀️ Test successful - checks-actions
Approved by: varkor
Pushing a609fb4 to master...

rust-highfive assigned varkor Dec 31, 2020

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varkor added the A-const-generics Area: const generics (parameters and arguments) label Dec 31, 2020

bors 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-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Dec 31, 2020

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bors 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-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Dec 31, 2020

lqd force-pushed the const_generics_defaults branch from d02ac5a to 2a01264 Compare December 31, 2020 19:18

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Dec 31, 2020

Dylan-DPC-zz mentioned this pull request Dec 31, 2020

Rollup of 8 pull requests #80566

Merged

bors 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-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jan 1, 2021

first pass at default values for const generics

61f33bf

- Adds optional default values to const generic parameters in the AST and HIR - Parses these optional default values - Adds a `const_generics_defaults` feature gate

lqd added 6 commits January 1, 2021 10:55

fix typo in feature gates file

5f4bb46

mark const_generics_defaults as an incomplete feature

ea8fa36

add test for the const_generics_defaults feature gate

64244b2

update min_const_generics tests using default values for const params

907ba75

The `const_generics_defaults` now handles them, and they correctly parse, so we can update these tests expecting a parser error .

adjust const generics defaults FIXMEs to the new feature gate

1fc3c4c

make const_generics_defaults use the unstable syntax mechanism

942b7ce

This is important to not accidentally stabilize the parsing of the syntax while it still is experimental and not formally accepted

lqd force-pushed the const_generics_defaults branch from 2a01264 to 942b7ce Compare January 1, 2021 10:21

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jan 1, 2021

bors added the merged-by-bors This PR was explicitly merged by bors. label Jan 1, 2021

bors merged commit a609fb4 into rust-lang:master Jan 1, 2021

rustbot added this to the 1.51.0 milestone Jan 1, 2021

This was referenced Jan 1, 2021

Small optimizations in macro derive #80259

Closed

Allow references to interior mutable data behind a feature gate #80418

Merged

lqd deleted the const_generics_defaults branch January 1, 2021 19:13

lqd mentioned this pull request Mar 11, 2021

implement feature(const_generics_defaults) #75384

Merged

lcnr mentioned this pull request Dec 11, 2021

Tracking issue for const generics (RFC 2000) #44580

Closed

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In which we start to parse const generics defaults #80547

In which we start to parse const generics defaults #80547

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In which we start to parse const generics defaults #80547

In which we start to parse const generics defaults #80547

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