cgen: fix anon struct auto string method generation

vlib/v/ast/table.v

@@ -46,6 +46,7 @@ pub mut:
 	pointer_size      int
 	// cache for type_to_str_using_aliases
 	cached_type_to_str map[u64]string
+	anon_struct_names  map[string]int // anon struct name -> struct sym idx
 }
 
 // used by vls to avoid leaks
@@ -834,6 +835,11 @@ pub fn (mut t Table) register_enum_decl(enum_decl EnumDecl) {
 	t.enum_decls[enum_decl.name] = enum_decl
 }
 
+[inline]
+pub fn (mut t Table) register_anon_struct(name string, sym_idx int) {
+	t.anon_struct_names[name] = sym_idx
+}
+
 pub fn (t &Table) known_type(name string) bool {
 	return t.find_type_idx(name) != 0 || t.parsing_type == name
 }

vlib/v/gen/c/cgen.v

@@ -1037,8 +1037,13 @@ fn (mut g Gen) write_results() {
 		}
 		done << base
 		g.typedefs.writeln('typedef struct $styp $styp;')
+		dump(g.result_type_text(styp, base))
 		g.out_results.write_string(g.result_type_text(styp, base) + ';\n\n')
 	}
+	for k, _ in g.table.anon_struct_names {
+		ck := c_name(k)
+		g.typedefs.writeln('typedef struct $ck $ck;')
+	}
 }
 
 fn (mut g Gen) find_or_register_shared(t ast.Type, base string) string {

vlib/v/gen/c/struct.v

@@ -350,7 +350,8 @@ fn (mut g Gen) struct_decl(s ast.Struct, name string, is_anon bool) {
 	g.type_definitions.writeln(pre_pragma)
 
 	if is_anon {
-		g.type_definitions.writeln('struct {')
+		g.type_definitions.write_string('\t$name ')
+		return
 	} else if s.is_union {
 		g.type_definitions.writeln('union $name {')
 	} else {

vlib/v/parser/struct.v

@@ -350,6 +350,9 @@ fn (mut p Parser) struct_decl(is_anon bool) ast.StructDecl {
 		return ast.StructDecl{}
 	}
 	mut ret := p.table.register_sym(sym)
+	if is_anon {
+		p.table.register_anon_struct(name, ret)
+	}
 	// allow duplicate c struct declarations
 	if ret == -1 && language != .c {
 		if _ := p.table.find_fn('main.main') {

vlib/v/tests/struct_test.v

@@ -447,3 +447,11 @@ fn test_anon() {
 	assert book2.author.age == 24
 	println(book2.author.name)
 }
+
+fn test_anon_auto_stringify() {
+	b := Book{}
+	s := b.str()
+	assert s.contains('author: ')
+	assert s.contains('name: ')
+	assert s.contains('age: 0')
+}