fmt: fix anonymous struct in parameter with invalid type name. fix #15696 (#15711)

vlib/v/ast/str.v

@@ -137,26 +137,41 @@ fn stringify_fn_after_name(node &FnDecl, mut f strings.Builder, t &Table, cur_mo
 			f.write_string(arg.typ.share().str() + ' ')
 		}
 		f.write_string(arg.name)
-		mut s := t.type_to_str(arg.typ.clear_flag(.shared_f))
-		if arg.is_mut {
-			arg_sym := t.sym(arg.typ)
-			if s.starts_with('&') && ((!arg_sym.is_number() && arg_sym.kind != .bool)
-				|| node.language != .v) {
-				s = s[1..]
+		arg_sym := t.sym(arg.typ)
+		if arg_sym.kind == .struct_ && (arg_sym.info as Struct).is_anon {
+			f.write_string(' struct {')
+			struct_ := arg_sym.info as Struct
+			for field in struct_.fields {
+				f.write_string(' $field.name ${t.type_to_str(field.typ)}')
+				if field.has_default_expr {
+					f.write_string(' = $field.default_expr')
+				}
 			}
-		}
-		s = util.no_cur_mod(s, cur_mod)
-		for mod, alias in m2a {
-			s = s.replace(mod, alias)
-		}
-		if should_add_type {
-			if !is_type_only {
+			if struct_.fields.len > 0 {
 				f.write_string(' ')
 			}
-			if node.is_variadic && is_last_arg {
-				f.write_string('...')
+			f.write_string('}')
+		} else {
+			mut s := t.type_to_str(arg.typ.clear_flag(.shared_f))
+			if arg.is_mut {
+				if s.starts_with('&') && ((!arg_sym.is_number() && arg_sym.kind != .bool)
+					|| node.language != .v) {
+					s = s[1..]
+				}
+			}
+			s = util.no_cur_mod(s, cur_mod)
+			for mod, alias in m2a {
+				s = s.replace(mod, alias)
+			}
+			if should_add_type {
+				if !is_type_only {
+					f.write_string(' ')
+				}
+				if node.is_variadic && is_last_arg {
+					f.write_string('...')
+				}
+				f.write_string(s)
 			}
-			f.write_string(s)
 		}
 		if !is_last_arg {
 			f.write_string(', ')

vlib/v/fmt/struct.v

@@ -253,7 +253,7 @@ pub fn (mut f Fmt) struct_init(node ast.StructInit) {
 		if node.pos.line_nr < node.pos.last_line || node.pre_comments.len > 0 {
 			single_line_fields = false
 		}
-		if !use_short_args {
+		if !use_short_args || node.is_anon {
 			f.write('$name{')
 			f.mark_import_as_used(name)
 			if single_line_fields {
@@ -315,7 +315,7 @@ pub fn (mut f Fmt) struct_init(node ast.StructInit) {
 		if !single_line_fields {
 			f.indent--
 		}
-		if !use_short_args {
+		if !use_short_args || node.is_anon {
 			if single_line_fields {
 				f.write(' ')
 			}

vlib/v/fmt/tests/anon_struct_as_param_expected.vv

@@ -0,0 +1,9 @@
+fn func(arg struct { foo string = 'bar' }) {
+	println(arg.foo)
+}
+
+fn main() {
+	func(struct {
+		foo: 'foo'
+	})
+}

vlib/v/fmt/tests/anon_struct_as_param_input.vv

@@ -0,0 +1,8 @@
+fn func(arg struct{foo string='bar'}) {
+	println(arg.foo)
+}
+
+fn main() {
+	func(struct {foo: 'foo'
+	})
+}