[SR-11170] SyntaxRewriter visitation exhausts the stack space that dispatch threads get

[tonyarnold]

[SR-11170] SyntaxRewriter visitation exhausts the stack space that dispatch threads get

[akyrtzi]

The problem is that the `SyntaxRewriter` visitation exhausts the stack space that dispatch threads get. This can be reproduced from a command-line tool by doing the formatting call on a dispatch queue other than the main one.

To workaround this run the formatting transformation under a pthread thread (which you can customize its stack allocation).

[akyrtzi]

Reproducer from a command-line tool:

import Foundation
import SwiftFormat
import SwiftFormatConfiguration
import SwiftSyntax

func doit() throws {
    let configuration = Configuration()
    let formatter = SwiftFormatter(configuration: configuration)
    let syntax = try SyntaxParser.parse(URL(fileURLWithPath: "/path/to/swift/file.swift"))
    let dummyFileURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(UUID().uuidString + ".swift")
    var output = String()
    try formatter.format(syntax: syntax, assumingFileURL: dummyFileURL, to: &output)
    print(output)
}
let q = DispatchQueue(label: "queue")
q.async {
    try! doit()
}
sleep(1)

[akyrtzi]

Here's how to fix this using `Thread`:

let work = DispatchWorkItem {
    doFormatting()
}
let thread = Thread {
    work.perform()
}
thread.stackSize = 8 << 20 // 8 MB.
thread.start()
work.wait()

[tonyarnold]

That did the trick! Thanks so much for the workaround, @akyrtzi - it works really nicely now.

[ahoppen]

The root issue of this is being tackled in swiftlang/swift-syntax#147 Once it‘s merged, the workaround using Thread should not be necessary anymore.