swiftlang / swiftlang/swift-experimental-string-processing
[Benchmark] Excessive (and expensive) backtracking
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- Dominant language
- Swift
- Stars
- 308
- Forks
- 52
- Avg merge
- 12h 45m
- Merged PRs (30d)
- 2
Description
From the forums:
let pattern = "^ +A"
let regex1 = try! NSRegularExpression(pattern: pattern)
let regex2 = try! Regex(pattern)
let numberOfSpaces = 50000
let testString = String(repeating: " ", count: numberOfSpaces)
let date = Date()
print(regex1.firstMatch(in: testString, range: .init(location: 0, length: numberOfSpaces)) == nil)
print(-date.timeIntervalSinceNow)
print(try! regex2.firstMatch(in: testString) == nil)
print(-date.timeIntervalSinceNow)
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the Swift reproduction in the issue with the 50,000-space input and compare the Regex and NSRegularExpression timings. Trace the Regex matching entry point involved in this pattern and verify that the excessive backtracking is removed without changing the match result.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- swift
- Domain
- performance
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100