task error handling

[jdx]

there should be some kind of error handling to execute something when a task fails, perhaps to cancel the error somehow. My use-case for this is I have a bunch of tasks that run and leave the project in an inconsistent state when they fail because it's all running in parallel. There is a specific task that—if failed—I'd like it to reset the contents of a specific file.

Noodling on this:

[tasks.render]
run = "node build-something.js > output"
on_failure = "git checkout output"

I don't personally need to cancel the error—though I feel like with this sort of thing that's probably going to be behavior someone wants—especially if I call this "error handling".

Maybe we could make that an optional setting:

[tasks.render]
run = "node build-something.js > output"
on_failure = {run = "git checkout output", cancel_error = true}

what do other task managers do?

[jdx]

perhaps a better way to name this would be "cleanup" and not worry about catching errors

[acesyde]

Maybe add the ability to only trigger the failure case on a specific exit code ?

[jdx]

I was going to pass the status code as an env var

[reteps]

The status code should be available in $? in my opinion for use in cleanup.

[jdx]

setting that before a script runs is complicated and something that would have to be unique depending on which shell is being used. Imagine a handler being written in python, for example.

[reteps]

Ah, you are correct. TIL: https://stackoverflow.com/a/26627346

[egnor]

You wouldn't just do something like this?

run = "node build-something.js > output || (git checkout output && false)"

...at some level a task runner isn't a full scripting language?

In general I'm a little suspicious of "cleanup" steps since if you control-C at the top level or something else happens you won't get your cleanup, so it's kind of a brittle thing to count on -- I would tend to encourage

run = [
  "node build-something.js > output.tmp",
  "mv output.tmp output",
]

but of course there are lots of examples where that's not so easy.