parser: check const declaration using multiple assign (#14886)

vlib/v/parser/parser.v

@@ -3364,6 +3364,9 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 				pos)
 		}
 		full_name := p.prepend_mod(name)
+		if p.tok.kind == .comma {
+			p.error_with_pos('const declaration do not support multiple assign yet', p.tok.pos())
+		}
 		p.check(.assign)
 		end_comments << p.eat_comments()
 		if p.tok.kind == .key_fn {

vlib/v/parser/tests/const_decl_err.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/const_decl_err.vv:6:3: error: const declaration do not support multiple assign yet
+    4 |
+    5 | const (
+    6 |     a, b, c = foo()
+      |      ^
+    7 | )
+    8 |

vlib/v/parser/tests/const_decl_err.vv

@@ -0,0 +1,12 @@
+fn foo() (int, int, int) {
+	return 1, 2, 3
+}
+
+const (
+	a, b, c = foo()
+)
+
+
+fn main() {
+	println("$a $b $c")
+}