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Standalone-Line Whitespace Stripping

Status: Supported for comments and section open / close tags.

Summary​

Mustache defines a "standalone line" as any line whose only non-whitespace content is a single tag from a specific set. When a line is standalone, the entire line - leading whitespace, the tag, and the trailing newline - is consumed from the output. Variable interpolation tags ({{x}}, {{{x}}}, {{&x}}) are deliberately excluded.

Bigodin applies this rule to:

  • Comments: {{! ... }}
  • Section openers and closers: {{#x}}, {{/x}}, {{^x}}

Set-delimiter, partial, and inheritance tags are not implemented in Bigodin, so the rule does not apply to them.

For explicit, greedier trimming that is not limited to standalone lines, use whitespace control ({{~ ~}}). When a tag side carries ~, it is handled by whitespace control and skips this standalone rule.

Hello
{{! a comment }}
World

renders as:

Hello
World

The leading whitespace and trailing newline on the comment line are both consumed.

Spec coverage​

All standalone-line tests in comments.json, sections.json, and inverted.json pass:

  • Standalone, Indented Standalone, Standalone Line Endings
  • Standalone Without Previous Line, Standalone Without Newline
  • Multiline Standalone, Indented Multiline Standalone
  • Standalone Lines, Indented Standalone Lines, Standalone Indented Lines

The standalone-line tests in delimiters.json and partials.json are skipped at the file level because the host features (set-delimiters, partials) are not implemented; the whitespace rule itself is not the blocker.

Implementation note​

Standalone stripping is a post-parse pass over the AST in src/parser/index.ts (stripStandaloneLines). It walks each statement list (top-level and every block's statements / elseStatements), looks at the surrounding TEXT statements, and trims leading/trailing whitespace where the line qualifies as standalone. Block openers are checked against the parent list's previous TEXT plus the first TEXT inside the block; block closers are checked against the last TEXT inside the block plus the parent list's next TEXT.

No AST shape change is required for this feature; whitespace edits live inside existing TextStatement.value.