Templated-YAML frontend: one parser for the Helm "YAML with holes" document language.

A Helm template is two interleaved languages: Go template actions with a real grammar (parsed by tree-sitter), and YAML layout recovered from the text between actions. This crate owns the second half. It tokenizes a template source into lines and action spans, then runs a layout parser over the indent structure, producing a [TemplatedDocument] CST in which YAML structure (mapping entries, sequence items, scalars, block scalars), template control regions (if/with/range/define/block with their branches), output holes, and comments are all first-class nodes carrying byte spans.

Dependency direction

helm-schema-syntax depends only on the tree-sitter grammar crate and is the single owner of the raw Go-template tree parse ([parse_go_template]). helm-schema-ast layers the typed expression AST (TemplateExpr) on top and re-exports this crate's YAML lexical helpers; it depends on this crate, never the reverse. Expression-level facts (toYaml-ness, nindent widths) intentionally stay out of the CST: the layout is decided by document shape alone, and expression semantics are applied by consumers that already own the expression parser.

Layout semantics and the line-model contract

Control actions in real charts frequently do not nest cleanly with YAML structure (a mapping entry opened inside an if branch can adopt children after {{ end }}). Container structure is therefore derived purely from the visible YAML lines by indent discipline — action-only lines, comments, and blanks are transparent to layout — and control regions are attached into the tree as first-class overlay nodes. Regions whose branch bodies align with whole nodes stay structured; regions that provably violate the well-nested assumption are flagged (or degraded to [Node::Opaque] when they open mid-scalar) instead of guessed at.

open-slot semantics that helm-schema-ast's attribution previously recovered with an O(n²) per-query line replay; here the parse is a single pass and each query is an O(depth) chain walk.