parser: add a better error message, for multiple attributes, used on the same struct field (#16954)

vlib/v/checker/tests/struct_multiple_attrs_test.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/struct_multiple_attrs_test.vv:4:10: error: multiple attributes should be in the same [], with ; separators
+    2 | 
+    3 | struct Test {
+    4 |     a int [a][b]
+      |             ~~
+    5 | }
+    6 |

vlib/v/checker/tests/struct_multiple_attrs_test.vv

@@ -0,0 +1,9 @@
+module main
+
+struct Test {
+	a int [a][b]
+}
+
+fn test_main() {
+	assert true
+}

vlib/v/parser/parser.v

@@ -60,6 +60,7 @@ mut:
 	inside_generic_params     bool // indicates if parsing between `<` and `>` of a method/function
 	inside_receiver_param     bool // indicates if parsing the receiver parameter inside the first `(` and `)` of a method
 	inside_struct_field_decl  bool
+	inside_struct_attr_decl   bool
 	inside_map_init           bool
 	or_is_handled             bool       // ignore `or` in this expression
 	builtin_mod               bool       // are we in the `builtin` module?
@@ -1773,6 +1774,11 @@ fn (mut p Parser) attributes() {
 		p.error_with_pos('attributes cannot be empty', p.prev_tok.pos().extend(p.tok.pos()))
 		return
 	}
+	if p.inside_struct_attr_decl && p.tok.kind == .lsbr {
+		p.error_with_pos('multiple attributes should be in the same [], with ; separators',
+			p.prev_tok.pos().extend(p.tok.pos()))
+		return
+	}
 }
 
 fn (mut p Parser) parse_attr() ast.Attr {

vlib/v/parser/struct.v

@@ -268,6 +268,7 @@ fn (mut p Parser) struct_decl(is_anon bool) ast.StructDecl {
 			// Comments after type (same line)
 			comments << p.eat_comments()
 			if p.tok.kind == .lsbr {
+				p.inside_struct_attr_decl = true
 				// attrs are stored in `p.attrs`
 				p.attributes()
 				for fa in p.attrs {
@@ -275,6 +276,7 @@ fn (mut p Parser) struct_decl(is_anon bool) ast.StructDecl {
 						is_field_deprecated = true
 					}
 				}
+				p.inside_struct_attr_decl = false
 			}
 			mut default_expr := ast.empty_expr
 			mut has_default_expr := false