check_match: fix handling of privately uninhabited types #47001
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kennytm
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src/librustc_const_eval/_match.rs
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| /// but not any of the sets in `m`. | ||
| /// This finds whether a (row) vector `v` of patterns is 'useful' in relation | ||
| /// to a set of such vectors `m` is defined as there being a set of inputs | ||
| /// that will match `v` but not any of the sets in `m`. |
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This sentence is not 100% grammatical. Maybe:
"This finds whether a (row) vector v of patterns is 'useful' in relation to a set of such vectors m; useful is defined as there being a set of inputs that will match v but not any of the sets in m."
src/librustc_const_eval/_match.rs
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| @@ -596,6 +602,9 @@ pub fn is_useful<'p, 'a: 'p, 'tcx: 'a>(cx: &mut MatchCheckCtxt<'a, 'tcx>, | |||
| assert!(rows.iter().all(|r| r.len() == v.len())); | |||
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| let pcx = PatternContext { | |||
| // () is used to represent an unknown type in this context. If | |||
| // one of the fields has a known type, use it instead (other | |||
| // than that, all types should be equal modulo normalization). | |||
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I don't really understand this comment. What is an unknown type here? And where is () being used?
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@nikomatsakis what do you want to do with this PR of ariel's? |
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@carols10cents good question =) I'll probably re-read it and try to write some comments myself, then merge it. |
the match-checking code used to use TyErr for signaling "unknown, inhabited" types for a long time. It had been switched to using the exact type in rust-lang#38069, to handle uninhabited types. However, in rust-lang#39980, we discovered that we still needed the "unknown inhabited" logic, but I used `()` instead of `TyErr` to handle that. Revert to using `TyErr` to fix that problem.
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I fixed the comments. |
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@bors r+ |
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📌 Commit 98fbcce has been approved by |
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check_match: fix handling of privately uninhabited types the match-checking code used to use TyErr for signaling "unknown, inhabited" types for a long time. It had been switched to using the exact type in #38069, to handle uninhabited types. However, in #39980, we discovered that we still needed the "unknown inhabited" logic, but I used `()` instead of `TyErr` to handle that. Revert to using `TyErr` to fix that problem. Fixes #46964. r? @nikomatsakis
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☀️ Test successful - status-appveyor, status-travis |
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the match-checking code used to use TyErr for signaling "unknown,
inhabited" types for a long time. It had been switched to using the
exact type in #38069, to handle uninhabited types.
However, in #39980, we discovered that we still needed the "unknown
inhabited" logic, but I used
()instead ofTyErrto handle that.Revert to using
TyErrto fix that problem.Fixes #46964.
r? @nikomatsakis