checker: make sure that the operator check is made on the concrete type (#13360)

vlib/v/checker/checker.v

@@ -541,10 +541,10 @@ pub fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 	defer {
 		c.expected_type = former_expected_type
 	}
-	left_type := c.expr(node.left)
+	mut left_type := c.expr(node.left)
 	node.left_type = left_type
 	c.expected_type = left_type
-	right_type := c.expr(node.right)
+	mut right_type := c.expr(node.right)
 	node.right_type = right_type
 	if left_type.is_number() && !left_type.is_ptr()
 		&& right_type in [ast.int_literal_type, ast.float_literal_type] {
@@ -796,6 +796,18 @@ pub fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 				} else if !left_sym.has_method('<') && node.op == .gt {
 					c.error('cannot use `>` as `<=` operator method is not defined', left_right_pos)
 				}
+			} else if left_type.has_flag(.generic) && right_type.has_flag(.generic) {
+				// Try to unwrap the generic type to make sure that
+				// the below check works as expected
+				left_gen_type := c.unwrap_generic(left_type)
+				gen_sym := c.table.sym(left_gen_type)
+				need_overload := gen_sym.kind in [.struct_, .interface_]
+				if need_overload && !gen_sym.has_method('<') && node.op in [.ge, .le] {
+					c.error('cannot use `$node.op` as `<` operator method is not defined',
+						left_right_pos)
+				} else if need_overload && !gen_sym.has_method('<') && node.op == .gt {
+					c.error('cannot use `>` as `<=` operator method is not defined', left_right_pos)
+				}
 			}
 		}
 		.left_shift {

vlib/v/checker/tests/cmp_between_struct.out

@@ -0,0 +1,21 @@
+vlib/datatypes/heap.v:16:15: error: cannot use `>` as `<=` operator method is not defined
+   14 |     mut child := heap.data.len - 1
+   15 |     mut parent := heap.parent(child)
+   16 |     for heap.data[parent] > heap.data[child] {
+      |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+   17 |         heap.data[parent], heap.data[child] = heap.data[child], heap.data[parent]
+   18 |         child = parent
+vlib/datatypes/heap.v:37:15: error: cannot use `>` as `<=` operator method is not defined
+   35 |     mut left := heap.left_child(parent) or { return item }
+   36 |     mut right := heap.right_child(parent) or { left }
+   37 |     for heap.data[parent] > heap.data[left] || heap.data[parent] > heap.data[right] {
+      |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~
+   38 |         // choose min for min heap
+   39 |         swap := if heap.data[left] <= heap.data[right] { left } else { right }
+vlib/datatypes/heap.v:39:23: error: cannot use `<=` as `<` operator method is not defined
+   37 |     for heap.data[parent] > heap.data[left] || heap.data[parent] > heap.data[right] {
+   38 |         // choose min for min heap
+   39 |         swap := if heap.data[left] <= heap.data[right] { left } else { right }
+      |                             ~~~~~~~~~~~~~~~~~~~~~~~~~~
+   40 |         heap.data[parent], heap.data[swap] = heap.data[swap], heap.data[parent]
+   41 |         parent = swap

vlib/v/checker/tests/cmp_between_struct.vv

@@ -0,0 +1,31 @@
+module main
+
+import datatypes
+
+struct Item {
+	priority int
+}
+
+// Issue https://github.com/vlang/v/issues/13318
+
+/*
+fn (a Item) < (b Item) bool {
+	return a.priority < b.priority
+}
+
+fn (a Item) == (b Item) bool {
+	return a.priority == b.priority
+}
+*/
+
+fn  main() {
+	min_heap()
+}
+
+fn min_heap() {
+	mut heap := datatypes.MinHeap<Item>{}
+
+	heap.insert(Item{10})
+
+	println(heap)
+}