Why parse only to ignore --stack-yaml in a script?

[philderbeast]

If a --stack-yaml option in a stack script is ignored then why is it parsed?

stack/src/Stack/Script.hs

Line 144 in 035ffea

"Ignoring override stack.yaml file for script command: "

If I comment out the resolver line then the parse fails:

message: "This is a stack.yaml file for a script."
allow-newer-deps:
  - dhall
allow-newer: true
# resolver: nightly-2024-05-18

I struck this when trying to set the resolver on-the-fly with:

$ GHC_VERSION=9.8.2 STACKAGE_VERSION=nightly-2024-05-18 make -f project-files.mk stack.yaml
...
Ignoring override stack.yaml file for script command: /.../stack.script.yaml

Error: [S-6602]
       Stack could not load and parse
       /.../stack.script.yaml as a YAML configuraton file.
       
       While loading and parsing, Stack encountered the following error:
       
       Aeson exception:
       Error in $: failed to parse field "snapshot": keys ["snapshot","resolver"] not present
       
       For help about the content of Stack's YAML configuration files, see (for the most recent
       release of Stack) http://docs.haskellstack.org/en/stable/yaml_configuration/.
...

This is the script header:

#!/usr/bin/env stack
-- stack script --resolver=nightly-2024-05-18 --package=base --package=dhall --package=filepath --package=text --stack-yaml=stack.script.yaml

[philderbeast]

Could script errors like these also have error codes? In this case something like:

Error: [S-NNNN]
       Ignoring override stack.yaml file for script command: /.../stack.script.yaml
           
       Overriding is not permitted with scripts.
       
       Either use inline options or the global project configuration in:
       ~/.stack/config.yaml (global configuration) or
       ~/.stack/config.yaml (project-level configuration)

[mpilgrem]

The short answer is that, currently, stack script uses other parts of the overall configuration, via withConfig, and the (ignored) stack.yaml configuration comes along for the ride. See module Stack.Script.

EDIT: I am wondering if the current behaviour is an unintended consequence of:

• stack script --use-root #6080

which is using unmodified global options to fetch the location of the Stack root.

[mpilgrem]

@philderbeast, the behaviour was indeed a regression introduced by #6080, it should be fixed by:

• Fix #6600 Don't use 'raw' withConfig with stack script #6601

[philderbeast]

Thanks for the quick fix @mpilgrem. I can confirm that the linked --stack-yaml=stack.script.yaml is ignored and not parsed. I also tried invalid YAML (with :, or %, or * as its single character content, verified as invalid by https://onlineyamltools.com/validate-yaml) as well as commenting out the resolver line.