checker, cgen: allow op overload for type with generic parent (#21262)

vlib/v/checker/infix.v

@@ -287,8 +287,8 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 					} else {
 						return_type = left_type
 					}
-				} else if left_final_sym.has_method(node.op.str()) {
-					if method := left_final_sym.find_method(node.op.str()) {
+				} else if left_final_sym.has_method_with_generic_parent(node.op.str()) {
+					if method := left_final_sym.find_method_with_generic_parent(node.op.str()) {
 						return_type = method.return_type
 					} else {
 						return_type = left_type

vlib/v/gen/c/infix.v

@@ -784,9 +784,16 @@ fn (mut g Gen) infix_expr_arithmetic_op(node ast.InfixExpr) {
 		if left.sym.has_method(node.op.str()) {
 			method = left.sym.find_method(node.op.str()) or { ast.Fn{} }
 			method_name = left.sym.cname + '_' + util.replace_op(node.op.str())
-		} else if left.unaliased_sym.has_method(node.op.str()) {
-			method = left.unaliased_sym.find_method(node.op.str()) or { ast.Fn{} }
+		} else if left.unaliased_sym.has_method_with_generic_parent(node.op.str()) {
+			method = left.unaliased_sym.find_method_with_generic_parent(node.op.str()) or {
+				ast.Fn{}
+			}
 			method_name = left.unaliased_sym.cname + '_' + util.replace_op(node.op.str())
+			if left.unaliased_sym.info is ast.Struct
+				&& left.unaliased_sym.info.generic_types.len > 0 {
+				method_name = g.generic_fn_name(left.unaliased_sym.info.concrete_types,
+					method_name)
+			}
 		} else {
 			g.gen_plain_infix_expr(node)
 			return

vlib/v/tests/operator_overloading_type_alias_generic_parent_test.v

@@ -0,0 +1,13 @@
+import math.vec
+
+type Vec3 = vec.Vec3[f64]
+
+fn test_operator_overloading_type_alias_generic_parent() {
+	a := Vec3{1.0, 2.0, 3.0}
+	b := Vec3{0.5, 1.5, 2.5}
+
+	assert a + b == Vec3{1.5, 3.5, 5.5}
+	assert a - b == Vec3{0.5, 0.5, 0.5}
+	assert a * b == Vec3{0.5, 3.0, 7.5}
+	assert a / b == Vec3{2.0, 1.3333333333333333, 1.2}
+}