Tracking issue for RFC 2535, 2530, 2175, "Or patterns, i.e Foo(Bar(x) | Baz(x))" · Issue #54883 · rust-lang/rust (original) (raw)

This is a tracking issue for the RFC "Or patterns, i.e Foo(Bar(x) | Baz(x))" (rust-lang/rfcs#2535).

The benefit of avoiding pat<no_top_alt> in as many places as possible would both be grammatical consistency and fewer surprises for uses. The drawbacks would be possible ambiguity or backtracking for closures and breakage for macros.

• On 2019-08-18, basic parsing landed in Initial implementation of or-patterns #61708 landed which was written by @dlrobertson and reviewed by @varkor, @Centril, @petrochenkov, @matthewjasper, and @alexreg.
• On 2019-08-27, full and polished parsing landed in Fully implement or-pattern parsing #63693 which was written by @Centril and reviewed by @estebank.
• On 2019-08-29, a typo in Fully implement or-pattern parsing #63693 was fixed in or-pattern: fix typo in error message #63938 which was written by @tshepang and reviewed by @Centril.
• On 2019-09-05, unused_parens: account for or-patterns and &(mut x) #64128, written by @Centril and reviewed by @davidtwco, landed. The PR fixed issue or_patterns: unused_parens lints erroneously on _a @ (0 | 1) #64106 where the compiler would spuriously emit unused_parens warnings on:
• ref? mut? x @ (p_0 | ... | p_n)
• box (p_0 | ... | p_n)
• & mut? (p_0 | ... | p_n)
• |(p_0 | ... | p_n)| $expr
• fn foo((p_0 | ... | p_n): $type)
• On 2019-09-06, or-patterns: Uniformly use PatKind::Or in AST & Fix/Cleanup resolve #64111, written by @Centril and reviewed by @petrochenkov, landed. The PR fixed the late-resolution behavior of or-patterns in nested positions including the already-bound check and binding-consistency check. Moreover, the AST now uniformly uses ast::PatKind::Or and has no special means of representing or-patterns at the top level.
• On 2019-09-25, or-patterns: Push PatKind/PatternKind::Or at top level to HIR & HAIR #64508, written by @Centril and reviewed by @matthewjasper, @varkor, and @nikomatsakis, landed. The PR adjusted the HIR and HAIR to consistently use or-patterns at the top & nested levels. Moreover, liveness, typeck, and dead_code analyses were adjusted also. Notably, The PR did however not adjust exhaustiveness checking. Tangentially, check_match: refactor + improve non-exhaustive diagnostics for default binding modes #64271, landed 2019-09-12, written by @Centril and reviewed by @estebank, adjusted check_match diagnostics logic to be better prepared for or-patterns.
• On 2019-09-29, syntax: recover trailing | in or-patterns #64887, written by @Centril and reviewed by @estebank, landed. The PR improved parser recovery for trailing | in pattern contexts.
• On 2019-10-27, Clarify pattern-matching usefulness algorithm #65874, written by @Nadrieril and reviewed by @varkor, @arielb1, @nnethercote, and @Centril, landed. The PR refactored the usefulness/exhaustiveness algorithm in match checking. This laid the foundation upon which exhaustiveness checking for or-patterns was later initially implemented in Initial implementation of or-pattern usefulness checking #66612.
• On 2019-11-23, resolve: more declarative fresh_binding #66639, written by @Centril and reviewed by @petrochenkov, landed. In this follow-up to or-patterns: Uniformly use PatKind::Or in AST & Fix/Cleanup resolve #64111, the resolve logic for adding fresh bindings was simplified and re-written in a more declarative fashion.
• On 2019-12-01, Initial implementation of or-pattern usefulness checking #66612, written by @Nadrieril and reviewed by @varkor, @Centril, and @matthewjasper, landed. In this follow-up to Clarify pattern-matching usefulness algorithm #65874, an initial implementation of exhaustiveness / usefulness checking for or-patterns was implemented.
• On 2019-12-03, Remove hack for top-level or-patterns in match checking #66967, written by @Nadrieril and reviewed by @varkor and @Centril, landed. In this follow-up to Initial implementation of or-pattern usefulness checking #66612, the top-level hack for or-patterns in exhaustiveness checking was removed, making or-patterns truly first-class in match checking.
• On 2019-12-21, is_binding_pat: use explicit match & include or-pats in grammar #67428, written by @Centril and reviewed by @matthewjasper, landed. This PR adjusted regionck's resolve_local::is_binding_pat such that the P& grammar includes or-patterns.
• On 2019-12-22, Cleanup lower_pattern_unadjusted & Improve slice pat typeck #67439, written by @Centril and reviewed by @matthewjasper, landed. Among other things, this PR simplified HAIR lowering of or-patterns a smidgen.
• On 2019-12-26, Prepare for lowering or-patterns #67592, written by @matthewjasper and reviewed by @Centril, landed. This PR did some preparatory cleanups in MIR lowering of match expressions before the MIR level support for or-patterns is added. Moreover, the PR gated or-patterns in const contexts under const_if_match.
• On 2020-02-04, Implement MIR lowering for or-patterns #67668, written by @matthewjasper and reviewed by @pnkfelix, @Centril, @nagisa, @varkor, and @eddyb, landed. The PR finally added the support for or-patterns in MIR building (dynamic semantics, borrow checking, ...). Now, nested or-patterns can actually be used on nightly with #![feature(or_patterns)].
• On 2020-02-06, or_patterns: add regression test for #68785 #68842, written by @Centril and reviewed by @estebank landed. The PR added a regression test for an issue fixed by Implement MIR lowering for or-patterns #67668.
• On 2020-02-15, typeck: clarify def_bm adjustments & add tests for or-patterns #68856, written by @Centril and reviewed by @matthewjasper landed. The PR polished the type checking of patterns with respect to default binding modes. In relation to or-patterns, the PR declared that or-patterns are pass-through (AdjustMode::Pass) in terms of default binding modes. This was already the case in the implementation (and already stabilized for top level or-patterns) but the PR removed the FIXME that left the question open.
• On 2020-02-28, 2020-03-08, and 2020-03-08, PRs typeck: use Pattern obligation cause more for better diagnostics #69452, check_binding_alt_eq_ty: improve precision wrt. if let #69599, and resolve, inconsistent binding mode: tweak wording #69687 landed. These were written by @Centril and were reviewed by @estebank, @davidtwco, and @estebank respectively. All PRs tweaked and improved diagnostics wrt. or-patterns.
• On 2020-03-08, test(pattern): add tests for combinations of pattern features #69690, written by @thekuom and reviewed by @Centril, landed. The relevant part of the PR added tests for the dynamic semantics of or-patterns combined with x @ y patterns, box patterns, and slice patterns.
• On 2020-03-10, test(patterns): add patterns feature tests to borrowck test suite #69817, written by @thekuom and reviewed by @Centril, landed. The PR added borrow checker tests in combination with other pattern features.
• On 2020-03-11, Exhaustiveness checking, Matrix::push: recursively expand or-patterns #69891, written by @Centril and reviewed by @varkor and @Nadrieril, landed. The PR fixed a bug (ICE "Or-pattern should have been expanded earlier on" #69875) in exhaustiveness checking where the patterns 0 | (1 | 2) and x @ 0 | x @ (1 | 2) would result in an ICE.
• On 2020-03-27, Fix incorrect pattern warning "unreachable pattern" #70413, written by @AminArria and reviewed by @varkor, @Nadrieril, and @Centril, landed. The PR fixed Incorrect "unreachable pattern" warning. #70372, a false positive in the linting behavior of unreachable_patterns when combining or-patterns, bindings, and guards.
• On 2020-04-13, Fix warning for unused variables in or pattern (issue #67691) #67766, written by @sapir and reviewed by @matthewjasper, landed. The PR fixed Incorrect unused_variables diagnostic for or-ed patterns #67691, a bug in the unused_variables lint pertaining to or-patterns.