compiler: add varg str method & varg / parser optimizations

vlib/compiler/comptime.v

@@ -331,7 +331,32 @@ fn (p mut Parser) gen_struct_str(typ Type) {
 	p.v.vgen_buf.writeln(sb.str())
 	// Need to manually add the definition to `fns` so that it stays
 	// at the top of the file.
-	// This function will get parsee by V after the main pass.
+	// This function will get parsed by V after the main pass.
+	p.cgen.fns << 'string ${typ.name}_str();'
+}
+
+fn (p mut Parser) gen_varg_str(typ Type) {
+	elm_type := typ.name[5..]
+	elm_type2 := p.table.find_type(elm_type)
+	is_array := elm_type.starts_with('array_')
+	if is_array {
+		p.gen_array_str(elm_type2)
+	} else if elm_type2.cat == .struct_ {
+		p.gen_struct_str(elm_type2)
+	}
+	p.v.vgen_buf.writeln('
+fn (a $typ.name) str() string {
+	mut sb := strings.new_builder(a.len * 3)
+	sb.write("[")
+	for i, elm in a {
+		sb.write(elm.str())
+		if i < a.len - 1 {
+			sb.write(", ")
+		}
+	}
+	sb.write("]")
+	return sb.str()
+}')
 	p.cgen.fns << 'string ${typ.name}_str();'
 }