Function emit_pest 

pub fn emit_pest(
    grammar: &Grammar,
) -> Result<(String, EmitReport), GrammarEmitError>

Emits pest PEG grammar text from the grammar IR.

pest maps closely to the grammar IR: ordered choice uses |, sequences use ~, predicates use &/!, and repetition forms are native. RuleKind::Token is emitted as pest’s compound-atomic $ rule modifier, the closest pest analogue to a token-level rule and the syntax a future round-trip importer should invert. Rust peg::parser! and winnow combinator emission follow the same PEG algebra but are intentionally left to the Rust codegen path.

Errors

Returns GrammarEmitError when the IR contains an internal invariant that cannot form valid pest text, such as an empty choice, an empty character class, a descending character range, or counted repetition with max < min.