Function widenBinding

packages/compiler/src/typecheck/ops/bindings.ts:169–189

(expr: TcbExpr, tcb: Context, originalValue: string | AST)

 * Potentially widens the type of `expr` according to the type-checking configuration.
 */
export function widenBinding(expr: TcbExpr, tcb: Context, originalValue: string | AST): TcbExpr {
  if (!tcb.env.config.checkTypeOfInputBindings) {
    // If checking the type of bindings is disabled, cast the resulting expression to 'any'
    // before the assignment.
    return new TcbExpr(`((${expr.print()}) as any)`);
  } else if (!tcb.env.config.strictNullInputBindings) {
    if (originalValue instanceof LiteralMap || originalValue instanceof LiteralArray) {
      // Object literals and array literals should not be wrapped in non-null assertions as that
      // would cause literals to be prematurely widened, resulting in type errors when assigning
      // into a literal type.
      return expr;
    } else {
      // If strict null checks are disabled, erase `null` and `undefined` from the type by
      // wrapping the expression in a non-null assertion.
      return new TcbExpr(`(${expr.print()})!`);
    }
  } else {
    // No widening is requested, use the expression as is.
    return expr;
  }
}