comptime expandable match statements

compiler/ast/ast.odin

@@ -180,7 +180,7 @@ Stmt :: struct {
 	immutable:  bool,
 	value_control_flow: bool,
 	pointer_capture: bool,
-	inline: bool,
+	expand: bool,
 	error_only: bool,
 	// Assignments store the lvalue in `target`, the right-hand side in `expr`,
 	// and the source operator in `assignment_op`. `Set` is ordinary `=`;
@@ -207,7 +207,8 @@ Stmt :: struct {
 	// list (empty marks the `else` arm; more than one is a multi-pattern arm),
 	// `captures` for the optional payload capture (0 or 1 name, tagged-union variants
 	// only) with `pointer_capture` distinguishing `|@cap|` from `|cap|`, and `body`
-	// as the arm body.
+	// as the arm body. An expanded arm has `expand` set, no patterns, and one or two
+	// captures for its specialized value/payload and optional tagged-union tag.
 	captures:   []symbol.Id,
 	// `Match_Arm` pattern list; empty ⇒ the `else` arm.
 	patterns:   []Expr_Id,