TUI::Form

Block-DSL sugar over FieldSpec(M) construction. Must be called as a bare top-level statement (not the right-hand side of an assignment) — the macro itself emits both a helper class declaration and the name = HelperClass.build assignment as two sibling top-level statements, since Crystal disallows a macro emitting a class declaration from expression/value position ("can't declare class dynamically").

Every field call still ends up as a literal m.prop/m.prop = v reference inside the generated self.build method — a property name that doesn't exist on the model is an ordinary Crystal "undefined method" compile error, not a silent no-op, PROVIDED the constant this macro assigns is actually read somewhere (Crystal skips type-checking of an unread top-level constant's initializer entirely — this macro can't change that ordinary Crystal semantic, so a TUI::Form.define block whose target constant is never referenced elsewhere would not be type-checked; every real call site passes the result straight into Form::Host, which reads it, so this is a non-issue in practice, but it means a spec exercising this safety guarantee must actually call .get/.set, not just assert "it compiles").