Function populate_ecmascript_compiler_facts 

pub fn populate_ecmascript_compiler_facts(
    index: &mut DeclIndex,
    tree: &Tree,
    file: FileId,
    src: &[u8],
)

Attach ECMAScript-specific syntax meaning to the language-neutral compiler IR. TypeScript deliberately reuses this lowering because its expression grammar extends ECMAScript; downstream engines see only typed boolean relations and exact decoded literal values.