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[SR-9206] Should literal Characters precondition on single-grapheme check? #51696

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milseman mannequin opened this issue Nov 7, 2018 · 3 comments
Open

[SR-9206] Should literal Characters precondition on single-grapheme check? #51696

milseman mannequin opened this issue Nov 7, 2018 · 3 comments
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@milseman
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself standard library Area: Standard library umbrella

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milseman mannequin commented Nov 7, 2018

Previous ID SR-9206
Radar rdar://problem/52193112
Original Reporter @milseman
Type Bug
Additional Detail from JIRA
Votes 0
Component/s Compiler, Standard Library
Labels Bug
Assignee @milseman
Priority Medium

md5: 1b44b077c8642a30055aca2f6e59d9ae

relates to:

  • SR-6077 Character ends up accepting invalid emoji flag sequences.

Issue Description:

String creation from a literal ends up calling the `unchecked` initializer to allow for better constant-folding, etc. But, the compiler can't be too overly restrictive, as what is and is not truly a grapheme is a runtime consideration, i.e. it has to support time-traveling. Thus, it's overly conservative about rejecting graphemes. The question is, should we keep emergent behavior or pay the cost of a precondition violation here?

See SuperChars.swift benchmark, which has a few multi-grapheme flag Characters in it.
@milseman
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milseman mannequin commented Nov 7, 2018

@eeckstein, what do you think here?

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milseman mannequin commented Nov 7, 2018

@swift-ci create

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milseman mannequin commented Nov 7, 2018

Chatted with @eeckstein. We think we'll add a single-scalar path that can be constant folded, and do a precondition check on multi-scalar Characters. We will also fix the benchmark to be correct. This will pollute history here a bit, but that's ok.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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@milseman milseman

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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself standard library Area: Standard library umbrella
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