Fable CLI 3.7 watch stales

[AngelMunoz]

Description

Hey! sorry to bother again
When invoking the fable cli 3.7.0-beta-* in watch mode through a library like CliWrap it never goes into watch mode this behavior is not observed in v3.6.3 using the same conditions

Fable: F# to JS compiler 3.7.0-beta-009
Thanks to the contributor! @fbehrens

Parsing src\fable37-cli.fsproj...
src> cmd /C dotnet restore fable37-cli.fsproj
  Determining projects to restore...
  All projects are up-to-date for restore.
Project and references (1 source files) parsed in 2125ms

Started Fable compilation...

Repro code

Here's a reproduction repository: https://github.com/AngelMunoz/fable37-cli

Expected and actual results

I expect to observe the same behavior as Fable 3.6.3, it should compile and start watching for file changes

Related information

• Fable version: dotnet fable --version: 3.7.0-beta-009
• Operating system: Windows 11

[AngelMunoz]

Note: invoking the CLI manually dotnet fable watch ./src/project.fsproj doesn't fail... so I'm not sure if it is related to something with a stdout redirect

[alfonsogarciacaro]

Ah, I see. Does watch mode doesn't work at all (no JS files are generated) or you just don't see the logs on screen? For Fable 3.7 I tried to bring back the one-line logs because they're very nice to see the progress of compilation:

But it may happen they don't play well with this CliWrap tool. I'm trying to disable the logs in CI where usually rewriting the same line is not possible. Maybe is there a way to also detect when the tool is being called as a subprocess?

Fable/src/Fable.Cli/Util.fs

Lines 79 to 91 in ac9bec8

	let inSameLineIfNotCI (msg: string) =
	if isVerbose() then
	Console.Out.WriteLine(msg)
	elif not isCi then
	// If the message is longer than the terminal width it will jump to next line
	let msg = if msg.Length > 80 then msg.[..80] + "..." else msg
	let curCursorLeft = Console.CursorLeft
	Console.SetCursorPosition(0, Console.CursorTop)
	Console.Out.Write(msg)
	let diff = curCursorLeft - msg.Length
	if diff > 0 then
	Console.Out.Write(String.replicate diff " ")
	Console.SetCursorPosition(msg.Length, Console.CursorTop)

[AngelMunoz]

I think they are generated, I need to check further, but CliWrap allows me to set env vars for the process perhaps I can add the CI env var, I'll test in a couple of hours and let you know

[AngelMunoz]

Well it weren't a few hours I could find a spot

I see. Does watch mode doesn't work at all (no JS files are generated)

I just checked and no, no files are generated at all

Setting the CI flag (.WithEnvironmentVariables(fun env -> env.Set("CI", "1") |> ignore)) does indeed make it work! it isn't as pretty but works nicely

[alfonsogarciacaro]

Hmm, interesting. So I guess that trying to move the cursor when being called from CliWrap is breaking/freezing the process somehow. Maybe opening an issue about that in CliWrap? Or you may need to spawn the process with its own shell.

[AngelMunoz]

Had a talk with CliWrap's author on discord he was kind enough to give this issue a glance

Hi. Moving the cursor should not affect CliWrap anyhow, however the actual code that does this (i.e. calling Console.SetCursorPosition in Fable compiler) would most likely throw. I don't remember exactly. Are you sure the process doesn't outright crash? If so, it might write something to stderr.

Interestingly it doesn't seem to throw or crash the process (maybe it does? I just know that the program keeps running waiting for the command to finish)

Also Alfonso said:

Maybe is there a way to also detect when the tool is being called as a subprocess?

You can do that by checking if the output is redirected via Console.IsOutputRedirected. If true, it's running through some automation tool and not in a shell.

You might be able to use this one instead of the CI env var possibly?

The best way to debug this would be to add Debugger.Attach() somewhere inside Fable compiler, probably put a breakpoint also in StreamPipeTarget (created by PipeTarget.ToStream(...), then call the CLI from CliWrap, and then see what happens exactly

I Will try to investigate further over the weekend if I have a chance in the meantime I can workaround this issue with the CI env var, I'll let you know if I find something

[alfonsogarciacaro]

Thanks for checking with CliWrap author @AngelMunoz! I've added the Console.IsOutputRedirected check, can you please try with beta-011?

[AngelMunoz]

Just in time before I go to sleep 😴 it worked!