Bootstrap compiler:
- ast.nim: add exprCallArgNames to ekCall for named arg tracking
- parser.nim: detect name: value syntax in call args
- sema.nim: add resolveCallArgs helper that injects default values
for missing params and reorders named args into param order.
Parser already parsed default param values; sema now uses them.
Selfhost compiler:
- ast.bux: add defaultExpr to Param, argName to ExprList
- parser.bux: parse = defaultExpr in param list, detect name: value
syntax in call arguments
- sema.bux: add Sema_ResolveCallArgs with same logic as bootstrap
Tests:
- _test_named_params verifies defaults, named args, mixed positional+named,
and named args with defaults in both compilers.
All verifications pass: build, selfhost-loop, test-examples, test-golden.