Opt-in function declarations

Date: 2026-04-23 Area: parser

Opt-in function declarations (--compat-function). Added function declaration and expression support behind a --compat-function CLI flag for ECMAScript compatibility when porting legacy code. Function declarations desugar to var-scoped bindings backed by TGocciaFunctionExpression, which produces call-site this binding (not lexical). Declarations are hoisted per ES spec: both name and value are available before the declaration is reached, using the same DefineVariableBinding infrastructure as --compat-var. Async functions are supported; generators (function*) and arguments remain excluded. No new AST node types — uses IsFunctionDeclaration flag on TGocciaVariableDeclaration. language.md § function Keyword.