dart format hangs on Windows when reading from stdin in the presubmit

[athomas]

The script below hangs on Windows but works fine on other platforms (change the hard coded depot_tools location in the script before running it):

#!/usr/bin/env python3

import imp
import os
import subprocess
import sys

depot_tools = '/Users/user/src/depot_tools'
sys.path.append(depot_tools)
import scm

utils = imp.load_source('utils', os.path.join('tools', 'utils.py'))
dart = os.path.join(utils.CheckedInSdkPath(), 'bin', 'dart')

windows = utils.GuessOS() == 'win32'
if windows:
    dart += '.exe'

args = [
    dart,
    'format',
    '--set-exit-if-changed',
    '--output=none',
    '--summary=none',
]

print('Body builder from git')
contents = scm.GIT.Capture(['show', 'c9d954efe7c7a71d2bf2c2ca385855b82fbfb379:pkg/front_end/lib/src/fasta/kernel/body_builder.dart'],
                                strip_out=False)
process = subprocess.run(args, input=contents, text=True)
print(process.returncode)

For some reason, dart format hangs reports weird formatting errors and starts to print messages like this:

Attempt:11 waiting for isolate vm-isolate to check in
Attempt:11 waiting for isolate dartdev to check in

On other platforms, the script exits normally and dart format finds no formatting issues.

@bkonyi @munificent Any ideas about what could go wrong here? Perhaps line ending confusion?

/cc @johnniwinther

[athomas]

Note that simpler test cases like these work even on Windows:

contents = """
void main()                     {}
"""
print('Format change')
process = subprocess.run(args, input=contents, text=True)
print(process.returncode)
 
contents = """
void main()                     {
"""
print('Syntax errror')
process = subprocess.run(args, input=contents, text=True)
print(process.returncode)
 
contents = """void main() {}
"""
print('No change')
process = subprocess.run(args, input=contents, text=True)
print(process.returncode)

[mraleph]

Is this a duplicate of #46600 (though that one was marked as fixed).

[athomas]

I don't think so. Before #46600, this would hang on macOS as well. Now it seems to only happen on Windows for specific inputs.

Also, a part of the fix was 44ffad5 which may have masked the issue. It removed the process.communicate causing the presubmit to no longer block on the dart format call. That broke the formatting check. This was fixed in d2bd43f which re-enabled the formatting checks.

[athomas]

The checked-in SDK is currently at 2.14.0-377.4.beta, which has the dart_style fixes for #44600.

[johnniwinther]

Any update on this? I am forced to upload most of my CLs with --bypass-hook because of this, and who knows how many badly formatted files have been committed due to this.

[munificent]

Sorry for the delay. I was out on vacation.

For some reason, dart format hangs reports weird formatting errors and starts to print messages like this:

Attempt:11 waiting for isolate vm-isolate to check in
Attempt:11 waiting for isolate dartdev to check in

I've never seen anything like that before, sorry. :( I also don't have a Windows machine to try to repro this on.

For what it's worth, dart_style does have tests for reading from stdin and I believe those tests are run and pass on Windows in the SDK. However, those tests also weren't sufficient to catch #46600. I don't recall exactly why. I think maybe because the tests spawn dart format not using a shell, which affects the behavior?

It looks like those messages are printed by the VM (DumpAliveIsolates()) when it is waiting for the isolates to shutdown? Maybe the main app isolate is hanging because it's waiting for more input on stdin or something?