[MillanWangShopify]

WHY are these changes introduced?

Closes https://github.com/shop/issues/issues/100399
Vault issue: https://vault.shopify.io/teams/16949-Dev-Experience/issues/92571-error-eisdir-illegal-operation-on-a-directory-read

shopify theme check -C . (or --config <dir>, with --print and --list too) crashes with EISDIR: illegal operation on a directory, read. Theme Check reads the config with readFile, and the failure is reported as an unhandled CLI error. Many CLIs use -C <dir> to mean "run in this directory", but here -C is the config file, and --path sets the theme folder.

WHAT is this pull request doing?

• Before loading, checks whether the explicitly selected config is a directory, and raises an AbortError with a next step for check, --print and --list. It checks up front because the EISDIR that readFile raises often has no path, so it can't be matched after the failure like the existing missing-file case.
• Resolves symlinks first (fileRealPath), because cli-kit's isDirectory uses lstat, so a symlink to a directory is caught too.
• Skips theme-check-node's ModernIdentifiers and missing paths, so missing files still produce "Theme Check config file not found".
• Makes the --config flag description say it takes a file path and that --path sets the theme directory.

Known limitation, to fix in Shopify/theme-tools: a directory named .theme-check.yml in the theme root (discovery only uses fs.stat), and extends: entries that point to a directory, still crash. Both need a theme-check-node release.

Before:

╭─ error ─╮  EISDIR: illegal operation on a directory, read

After:

Theme Check config must be a file, but . is a directory.
Pass the path to a .theme-check.yml file to --config, or omit --config to use the .theme-check.yml in your theme root. To choose the theme directory, use --path.

How to manually test your changes?

cd <any theme directory>
pnpm shopify theme check -C .
pnpm shopify theme check --config . --print
pnpm shopify theme check --config theme-check:recommended
pnpm shopify theme check --config ./missing.yml

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

[karreiro]

Thank you, @MillanWangShopify!