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Span

Given the original YAML source text and a path through the document (e.g. ["sources", "brew", "version"]), this module returns the super::Span of the matching key so diagnostic renderers can underline the exact region of the user’s file.

Algorithm

The mapper scans the YAML source line-by-line. For each key-path component it looks for a line that:

  1. Begins at the expected indentation level (two-space YAML indent assumed, common in stackie block files and serde_yaml output).
  2. Starts with the expected key name followed by :.

When the full path is consumed the span covers that single key line. This handles the vast majority of block/stack validation errors without requiring a full YAML scanner with position tracking.

Limitations

  • Assumes two-space indentation (consistent with all stackie YAML files).
  • Does not handle multi-document YAML or aliases.
  • Returns None when the key path is empty or the key is not found.