Add check for overlapping ranges to unreachable patterns lint #64007

estebank · 2019-08-29T23:11:23Z

rust-highfive · 2019-08-29T23:11:26Z

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estebank · 2019-08-29T23:15:01Z

Should this be separated to new lint instead of overloading unreachable_patterns?

I'm explicitly not handling the "multiple holes caught by _" case because it has the potential of being extremely annoying. It likely belongs in clippy complaining about _ being bad style.

CC @varkor @oli-obk @Centril

varkor · 2019-08-29T23:24:13Z

I'll look at the code more closely later, but I think this should be pulled out into its own lint, as I think there are legitimate reasons to want overlapping ranges (though overlapping by a single element seems less intentional).

src/librustc_mir/hair/pattern/_match.rs

src/librustc_mir/hair/pattern/check_match.rs

src/librustc_mir/hair/pattern/_match.rs

joshtriplett · 2019-09-05T19:40:19Z

Conclusions from the lang team meeting:

We think there are legitimate use cases for some kinds of overlaps. For instance, matching a couple of specific letters and then matching a whole range that covers those letters as a fallback.
Thus, we think this would be prone to false positives.
We think some heuristics might help with that. For instance, overlapping ranges that don't completely overlap (0..10 and 5..15) seem more reasonable to warn about, rather than 5..10 and 0..20.

Because of that, we think this should be in clippy.

scottmcm · 2019-09-05T19:47:43Z

I feel strongly that this shouldn't be unreachable_patterns because the arm is reachable.

My interpretation here is that this needs to be heuristic-heavy, so it being in clippy sounds fine. But if there's some obvious simple heuristic that's essentially always correct I have no objection to having it in the compiler. (Maybe something like "the fix is just to change a literal to a different literal".)

estebank · 2019-09-05T20:27:39Z

I could restrict this new lint to single element overlap (0..=10/10..=20) and disjointed partial overlaps (0..10/5..15) and ignore the common desired case (100..102/0..=255). That would cover the cases I was worried about to begin with. Is this reasonable? I don't mind dropping this and relying on clippy instead :)

Centril · 2019-09-05T20:31:47Z

I think going for the single element overlap (just for ranges) is something I'd be OK with in rustc.

joshtriplett · 2019-09-12T15:01:34Z

On September 5, 2019 1:32:55 PM PDT, Mazdak Farrokhzad ***@***.***> wrote: I think going for the single element overlap (just for ranges) is something I'd be OK with in rustc.

Likewise. Good idea.

hdhoang · 2019-09-20T01:50:00Z

ping from triage @estebank, any update after the reviewers' comment?

JohnCSimon · 2019-09-27T23:57:07Z

Pinging again from triage.
@estebank Can you please address the merge conflicts.
Thanks!

JohnCSimon · 2019-10-05T18:47:32Z

Hello from triage:
@estebank -
This PR has sat idle for awhile, so I'm closing it as inactive,
Please reopen this when you have time to resolve the merge conflicts.

Thank you!

matthewjasper

@Centril should this be changed to only lint on single element overlap?

src/test/ui/issues/issue-13867.rs

Centril · 2019-10-16T10:06:42Z

@Centril should this be changed to only lint on single element overlap?

Yes, let's start conservative for now with the consensus that is expressed in the PR discussion and we can consider expanding the scope later on. Possibly also file an issue for considering the scope-expansion and tag T-lang (maybe also dump the existing code there for keep-sakes).

…atterns

estebank · 2019-10-16T19:23:12Z

@Centril done and done.

matthewjasper · 2019-10-19T10:43:38Z

@bors r+

bors · 2019-10-19T10:43:39Z

📌 Commit 593cdcc has been approved by matthewjasper

…tthewjasper Add check for overlapping ranges to unreachable patterns lint Fix rust-lang#63987.

@ghost

Rollup of 5 pull requests Successful merges: - #64007 (Add check for overlapping ranges to unreachable patterns lint) - #65192 (Use structured suggestion for restricting bounds) - #65226 (BTreeSet symmetric_difference & union optimized) - #65448 (rustc_codegen_ssa: remove some unnecessary Box special-casing.) - #65505 (Rc: value -> allocation) Failed merges: r? @ghost

Refactor integer range handling in the usefulness algorithm Integer range handling had accumulated a lot of debt. This cleans up a lot of it. In particular this: - removes unnecessary conversions between `Const` and `u128`, and between `Constructor` and `IntRange` - clearly distinguishes between on the one hand ranges of integers that may or may not be matched exhaustively, and on the other hand ranges of non-integers that are never matched exhaustively and are compared using Const-based shenanigans - cleans up some overly complicated code paths - generally tries to be more idiomatic. As a nice side-effect, I measured a 10% perf increase on `unicode_normalization`. There's one thing that I feel remains to clean up: the [overlapping range check](#64007), which is currently quite ad-hoc. But that is intricate enough that I'm leaving it out of this PR. There's also one little thing I'm not sure I understand: can `try_eval_bits` fail for an integer constant value in that code ? What would that mean, and how do I construct a test case for this possibility ?

rust-highfive assigned matthewjasper Aug 29, 2019

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estebank force-pushed the overlapping-patterns branch from 6bb131c to cd6d7ba Compare August 29, 2019 23:12

estebank force-pushed the overlapping-patterns branch from cd6d7ba to 2731c02 Compare August 29, 2019 23:24

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estebank force-pushed the overlapping-patterns branch from ea4ab95 to 4a8d83e Compare August 30, 2019 00:57

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estebank added 10 commits October 16, 2019 11:57

Add check for overlapping ranges to unreachable patterns lint

91a3db9

Move overlapping patterns to its own lint

220b9b2

Silence lint in fit_signed and fit_unsigned

916936c

Move lint emitter to its own method

d2cb5a8

review comments: use if let

be9e6af

Deduplicate code for formatting RangeEnd

1ec6073

rename method

6832da8

Continue to emit unreachable pattern on cases caught by overlapping p…

89b19cc

…atterns

Only emit overlapping patterns lint if the overlap is partial

73d6efc

Lint only on single element overlap

593cdcc

estebank force-pushed the overlapping-patterns branch from c19d1a2 to 593cdcc Compare October 16, 2019 19:22

estebank mentioned this pull request Oct 16, 2019

Extend overlapping ranges lint to cover cases with more than a single element overlapping #65477

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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-review Status: Awaiting review from the assignee but also interested parties. labels Oct 19, 2019

Centril added a commit to Centril/rust that referenced this pull request Oct 19, 2019

Rollup merge of rust-lang#64007 - estebank:overlapping-patterns, r=ma…

53a3bfc

…tthewjasper Add check for overlapping ranges to unreachable patterns lint Fix rust-lang#63987.

Centril mentioned this pull request Oct 19, 2019

Rollup of 5 pull requests #65598

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bors merged commit 593cdcc into rust-lang:master Oct 19, 2019

Nadrieril mentioned this pull request Nov 12, 2019

Refactor integer range handling in the usefulness algorithm #66326

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estebank deleted the overlapping-patterns branch November 9, 2023 05:18

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Add check for overlapping ranges to unreachable patterns lint #64007

Add check for overlapping ranges to unreachable patterns lint #64007

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Add check for overlapping ranges to unreachable patterns lint #64007

Add check for overlapping ranges to unreachable patterns lint #64007

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