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BridgeJS: show unified diff on snapshot mismatch #600

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Merged
kateinoigakukun merged 1 commit into from
Feb 8, 2026
Merged

BridgeJS: show unified diff on snapshot mismatch #600

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41 changes: 35 additions & 6 deletions Plugins/BridgeJS/Tests/BridgeJSToolTests/SnapshotTesting.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -22,17 +22,26 @@ func assertSnapshot(

if FileManager.default.fileExists(atPath: snapshotPath.path) {
let existingSnapshot = try String(contentsOf: snapshotPath, encoding: .utf8)
let ok = existingSnapshot == String(data: input, encoding: .utf8)!
let actual = String(data: input, encoding: .utf8)!
let ok = existingSnapshot == actual
let actualFilePath = snapshotPath.path + ".actual"
let updateSnapshots = ProcessInfo.processInfo.environment["UPDATE_SNAPSHOTS"] != nil
func buildComment() -> Comment {
"Snapshot mismatch: \(actualFilePath) \(snapshotPath.path)"
}

if !updateSnapshots {
#expect(ok, buildComment(), sourceLocation: sourceLocation)
if !ok {
try input.write(to: URL(fileURLWithPath: actualFilePath))
try actual.write(toFile: actualFilePath, atomically: true, encoding: .utf8)
}

let diff = ok ? nil : unifiedDiff(expectedPath: snapshotPath.path, actualPath: actualFilePath)
func buildComment() -> Comment {
var message = "Snapshot mismatch: \(actualFilePath) \(snapshotPath.path)"
if let diff {
message.append("\n\n" + diff)
}
return Comment(rawValue: message)
}

#expect(ok, buildComment(), sourceLocation: sourceLocation)
} else {
try input.write(to: snapshotPath)
}
Expand All @@ -41,3 +50,23 @@ func assertSnapshot(
#expect(Bool(false), "Snapshot created at \(snapshotPath.path)", sourceLocation: sourceLocation)
}
}

private func unifiedDiff(expectedPath: String, actualPath: String) -> String? {
let process = Process()
process.executableURL = URL(fileURLWithPath: "/usr/bin/env")
process.arguments = ["diff", "-u", expectedPath, actualPath]
let output = Pipe()
process.standardOutput = output
process.standardError = Pipe()

do {
try process.run()
} catch {
return nil
}
process.waitUntilExit()
Comment on lines +58 to +67
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Copilot AI Feb 8, 2026

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process.standardError is set to a Pipe() but never read. This can both drop useful error output (e.g., diff errors) and has the same pipe-buffer deadlock risk as stdout. Either read stderr as well, or redirect stderr to stdout / a file, and consider checking terminationStatus (0=same, 1=different, 2=error) to decide what to return.

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let data = output.fileHandleForReading.readDataToEndOfFile()
Comment on lines +55 to +69
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Copilot AI Feb 8, 2026

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unifiedDiff runs diff with Pipe() output but waits for the process to exit before reading. If the unified diff is large enough to fill the pipe buffer, the child process can block on write and waitUntilExit() can hang the test run. Consider draining stdout/stderr while the process runs (e.g., readabilityHandler like invokeTS2Swift does) or redirecting output to a temporary file and reading it after exit.

Copilot uses AI. Check for mistakes.
guard !data.isEmpty else { return nil }
return String(data: data, encoding: .utf8)
}