Set brackets on TypeList in parser (#448)

Add a setter for brackets on `TypeList` and set them in the parser.

Author: doriable

experimental/ast/type_generic.go

@@ -126,6 +126,12 @@ func (d TypeList) Brackets() token.Token {
 	return d.raw.brackets.In(d.Context())
 }
 
+// SetBrackets sets the token tree for the brackets wrapping the argument list.
+func (d TypeList) SetBrackets(brackets token.Token) {
+	d.Context().Nodes().panicIfNotOurs(brackets)
+	d.raw.brackets = brackets.ID()
+}
+
 // Len implements [seq.Indexer].
 func (d TypeList) Len() int {
 	if d.IsZero() {
@@ -140,7 +146,7 @@ func (d TypeList) At(n int) TypeAny {
 	return newTypeAny(d.Context(), d.raw.args[n].Value)
 }
 
-// At implements [seq.Setter].
+// SetAt implements [seq.Setter].
 func (d TypeList) SetAt(n int, ty TypeAny) {
 	d.Context().Nodes().panicIfNotOurs(ty)
 	d.raw.args[n].Value = ty.raw

experimental/parser/parse_decl.go

@@ -371,6 +371,7 @@ func parseRange(p *parser, c *token.Cursor) ast.DeclRange {
 
 // parseTypeList parses a type list out of a bracket token.
 func parseTypeList(p *parser, parens token.Token, types ast.TypeList, in taxa.Noun) {
+	types.SetBrackets(parens)
 	delimited[ast.TypeAny]{
 		p:    p,
 		c:    parens.Children(),