vfmt: fix comments before ...f in Abc{...f} (#7870)

vlib/v/ast/ast.v

@@ -254,6 +254,7 @@ pub mut:
 	typ                  table.Type
 	update_expr          Expr
 	update_expr_type     table.Type
+	update_expr_comments []Comment
 	has_update_expr      bool
 	fields               []StructInitField
 	embeds               []StructInitEmbed

vlib/v/fmt/fmt.v

@@ -2054,13 +2054,14 @@ pub fn (mut f Fmt) struct_init(it ast.StructInit) {
 		}
 		init_start := f.out.len
 		f.indent++
+		short_args_loop: for {
+			f.comments(it.pre_comments, inline: true, has_nl: true, level: .keep)
 			if it.has_update_expr {
 				f.write('...')
 				f.expr(it.update_expr)
 				f.writeln('')
+				f.comments(it.update_expr_comments, inline: true, has_nl: true, level: .keep)
 			}
-		short_args_loop: for {
-			f.comments(it.pre_comments, inline: true, has_nl: true, level: .keep)
 			for i, field in it.fields {
 				f.write('$field.name: ')
 				f.prefix_expr_cast_expr(field.expr)

vlib/v/fmt/tests/struct_update_comment_keep.vv

@@ -0,0 +1,18 @@
+struct Foo {
+	name string
+	age  int
+}
+
+struct Foo2 {}
+
+fn main() {
+	f := Foo{
+		name: 'test'
+		age: 18
+	}
+	f2 := Foo{
+		// before
+		...f // after
+		name: 'f2'
+	}
+}

vlib/v/parser/struct.v

@@ -336,6 +336,7 @@ fn (mut p Parser) struct_init(short_syntax bool) ast.StructInit {
 	saved_is_amp := p.is_amp
 	p.is_amp = false
 	mut update_expr := ast.Expr{}
+	mut update_expr_comments := []ast.Comment{}
 	mut has_update_expr := false
 	for p.tok.kind !in [.rcbr, .rpar, .eof] {
 		mut field_name := ''
@@ -353,6 +354,7 @@ fn (mut p Parser) struct_init(short_syntax bool) ast.StructInit {
 			// struct updating syntax; f2 := Foo{ ...f, name: 'f2' }
 			p.check(.ellipsis)
 			update_expr = p.expr(0)
+			update_expr_comments << p.eat_line_end_comments()
 			has_update_expr = true
 		} else {
 			first_field_pos := p.tok.position()
@@ -394,6 +396,7 @@ fn (mut p Parser) struct_init(short_syntax bool) ast.StructInit {
 		typ: typ
 		fields: fields
 		update_expr: update_expr
+		update_expr_comments: update_expr_comments
 		has_update_expr: has_update_expr
 		pos: token.Position{
 			line_nr: first_pos.line_nr