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[6.4] Fix forward progress check for lookahead, attempt 2 #869

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Merged
natecook1000 merged 2 commits into from
Jul 22, 2026
Merged

[6.4] Fix forward progress check for lookahead, attempt 2 #869

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67c5691
Fix forward progress detection for lookaround groups (#866)
ekassos Jul 21, 2026
3403183
Add'l testing for lookahead forward prog detection (#867)
natecook1000 Jul 21, 2026
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2 changes: 2 additions & 0 deletions Sources/_StringProcessing/ByteCodeGen+DSLList.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -369,6 +369,8 @@ fileprivate extension Compiler.ByteCodeGen {
case .nonCapturingGroup(let kind):
switch kind.ast {
case .lookahead, .negativeLookahead, .lookbehind, .negativeLookbehind:
list.skipNode(&position)
position += 1
return false
default:
return _guaranteesForwardProgressImpl(list, position: &position)
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3 changes: 3 additions & 0 deletions Tests/RegexTests/CompileTests.swift
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Expand Up @@ -531,6 +531,9 @@ extension RegexTests {
expectProgram(for: #"(?:\w|(?i))+"#, contains: [.moveCurrentPosition, .condBranchSamePosition])
expectProgram(for: #"(?:A*(?:b|c*))*"#, contains: [.moveCurrentPosition, .condBranchSamePosition])
expectProgram(for: #"(?:[^/]*(?:/|$))*"#, contains: [.moveCurrentPosition, .condBranchSamePosition])
expectProgram(for: #"(?:(?=a)\d*)*"#, contains: [.moveCurrentPosition, .condBranchSamePosition])
expectProgram(for: #"(?:(?!a)\d*)*"#, contains: [.moveCurrentPosition, .condBranchSamePosition])
expectProgram(for: #"(?:(?!\d)[0-9]*)*"#, contains: [.moveCurrentPosition, .condBranchSamePosition])

// Bounded quantification, don't emit position checking
expectProgram(for: #"(?:(?=a)){1,4}"#, doesNotContain: [.moveCurrentPosition, .condBranchSamePosition])
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22 changes: 20 additions & 2 deletions Tests/RegexTests/MatchTests.swift
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Expand Up @@ -2828,15 +2828,27 @@ extension RegexTests {
}
}

func expectCompletion(regex: String, in target: String) {
func expectCompletion(
regex: String,
in target: String,
file: StaticString = #file,
line: UInt = #line
) {
let expectation = XCTestExpectation(description: "Run the given regex to completion")
Task.init {
let r = try! Regex(regex)
let val = target.matches(of: r).isEmpty
expectation.fulfill()
return val
}
wait(for: [expectation], timeout: 3.0)
let result = XCTWaiter().wait(for: [expectation], timeout: 3.0)
if result != .completed {
XCTFail("""
Matching didn't complete within 3 seconds:
regex: \(regex)
input: \(target)
""", file: file, line: line)
}
}

func testQuantificationForwardProgress() {
Expand All @@ -2856,6 +2868,12 @@ extension RegexTests {

expectCompletion(regex: #"(?:A*(?:b|c*))*"#, in: "ABC")
expectCompletion(regex: #"^(?:(?:[^/]*(?:/|$))*)(?:[^/]*)$"#, in: "Sources/main.swift")

// Repeated lookahead
expectCompletion(regex: #"(?:(?=\w)\d*)*"#, in: "a")
expectCompletion(regex: #"(?:(?=\d)\w*)*"#, in: "a")
expectCompletion(regex: #"(?:(?!b)\d*)*"#, in: "a")
expectCompletion(regex: #"(?:(?!\d)[0-9]*)*"#, in: "a")
}

func testQuantifyOptimization() throws {
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