checker,parser,ast: make type MyBuilder = strings.Builder work (part 1); add mod fields to ast.SumTypeDecl and ast.AliasTypeDecl (#25943)

Author: spytheman

cmd/tools/vast/vast.v

@@ -873,6 +873,7 @@ fn (t Tree) alias_type_decl(node ast.AliasTypeDecl) &Node {
 	mut obj := create_object()
 	obj.add_terse('ast_type', t.string_node('AliasTypeDecl'))
 	obj.add_terse('name', t.string_node(node.name))
+	obj.add_terse('mod', t.string_node(node.mod))
 	obj.add_terse('typ', t.type_node(node.typ))
 	obj.add_terse('parent_type', t.type_node(node.parent_type))
 	obj.add_terse('is_pub', t.bool_node(node.is_pub))
@@ -885,6 +886,7 @@ fn (t Tree) sum_type_decl(node ast.SumTypeDecl) &Node {
 	mut obj := create_object()
 	obj.add_terse('ast_type', t.string_node('SumTypeDecl'))
 	obj.add_terse('name', t.string_node(node.name))
+	obj.add_terse('mod', t.string_node(node.mod))
 	obj.add_terse('is_pub', t.bool_node(node.is_pub))
 	obj.add('pos', t.pos(node.pos))
 	obj.add_terse('typ', t.type_node(node.typ))

vlib/v/ast/ast.v

@@ -1508,6 +1508,7 @@ pub mut:
 pub struct AliasTypeDecl {
 pub:
 	name     string
+	mod      string
 	is_pub   bool
 	typ      Type
 	pos      token.Pos
@@ -1523,6 +1524,7 @@ pub mut:
 pub struct SumTypeDecl {
 pub:
 	name          string
+	mod           string
 	is_pub        bool
 	pos           token.Pos
 	name_pos      token.Pos

vlib/v/checker/checker.v

@@ -618,7 +618,10 @@ fn (mut c Checker) alias_type_decl(mut node ast.AliasTypeDecl) {
 		}
 		.alias {
 			orig_sym := c.table.sym((parent_typ_sym.info as ast.Alias).parent_type)
-			if !node.name.starts_with('C.') {
+			if !node.name.starts_with('C.')
+				&& parent_typ_sym.name !in ['strings.Builder', 'StringBuilder', 'builtin.StringBuilder'] {
+				// TODO: remove the whole check, or at least the need for special casing `strings.Builder` and `StringBuilder` here
+				// after more testing and bootstrapping of the strings.Builder -> builtin.StringBuilder change
 				c.error('type `${parent_typ_sym.str()}` is an alias, use the original alias type `${orig_sym.name}` instead',
 					node.type_pos)
 			}

vlib/v/parser/parser.v

@@ -3007,6 +3007,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 		}
 		node := ast.SumTypeDecl{
 			name:          name
+			mod:           p.mod
 			typ:           typ
 			is_pub:        is_pub
 			variants:      sum_variants
@@ -3072,6 +3073,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 	p.attrs = []
 	alias_type_decl := ast.AliasTypeDecl{
 		name:        name
+		mod:         p.mod
 		is_pub:      is_pub
 		typ:         idx
 		parent_type: parent_type