v.gen.js: support operator overloading (#11171)

vlib/v/gen/js/js.v

@@ -428,6 +428,9 @@ fn (mut g JsGen) js_name(name_ string) string {
 			'*' {
 				'\$mul'
 			}
+			'%' {
+				'\$mod'
+			}
 			'==' {
 				'eq'
 			}
@@ -1769,8 +1772,14 @@ fn (mut g JsGen) gen_infix_expr(it ast.InfixExpr) {
 	}
 
 	if it.op == .eq || it.op == .ne {
+		has_operator_overloading := g.table.type_has_method(l_sym, '==')
+		if has_operator_overloading {
+			g.expr(it.left)
+			g.write('.eq(')
+			g.expr(it.right)
+			g.write(')')
 			// Shallow equatables
-		if l_sym.kind in js.shallow_equatables && r_sym.kind in js.shallow_equatables {
+		} else if l_sym.kind in js.shallow_equatables && r_sym.kind in js.shallow_equatables {
 			// wrap left expr in parens so binary operations will work correctly.
 			g.write('(')
 			g.expr(it.left)
@@ -1816,9 +1825,52 @@ fn (mut g JsGen) gen_infix_expr(it ast.InfixExpr) {
 		g.expr(it.left)
 		g.write(' instanceof ')
 		g.write(g.typ(it.right_type))
+	} else if it.op in [.lt, .gt, .ge, .le] && g.table.type_has_method(l_sym, '<')
+		&& l_sym.kind == r_sym.kind {
+		if it.op in [.le, .ge] {
+			g.write('!')
+		}
+		if it.op in [.lt, .ge] {
+			g.expr(it.left)
+			g.write('.\$lt (')
+			g.expr(it.right)
+			g.write(')')
+		} else {
+			g.expr(it.right)
+			g.write('.\$lt (')
+			g.expr(it.left)
+			g.write(')')
+		}
 	} else {
 		is_arithmetic := it.op in [token.Kind.plus, .minus, .mul, .div, .mod]
-
+		has_operator_overloading := g.table.type_has_method(l_sym, it.op.str())
+		if has_operator_overloading {
+			g.expr(it.left)
+			name := match it.op.str() {
+				'+' {
+					'\$add'
+				}
+				'-' {
+					'\$sub'
+				}
+				'/' {
+					'\$div'
+				}
+				'*' {
+					'\$mul'
+				}
+				'%' {
+					'\$mod'
+				}
+				else {
+					panic('unreachable')
+					''
+				}
+			}
+			g.write('.$name (')
+			g.expr(it.right)
+			g.write(')')
+		} else {
 			mut greater_typ := 0
 			// todo(playX): looks like this cast is always required to perform .eq operation on types.
 			if is_arithmetic {
@@ -1847,6 +1899,7 @@ fn (mut g JsGen) gen_infix_expr(it ast.InfixExpr) {
 				g.write(')')
 			}
 		}
+	}
 
 	if is_not {
 		g.write(')')

vlib/v/gen/js/tests/testdata/overloading.out

@@ -0,0 +1,3 @@
+Foo { x: 5 , y: 5 }
+true
+true

vlib/v/gen/js/tests/testdata/overloading.v

@@ -0,0 +1,24 @@
+struct Foo {
+	x f32
+	y f32
+}
+
+pub fn (x Foo) == (y Foo) bool {
+	return x.x == y.y
+}
+
+pub fn (x Foo) < (y Foo) bool {
+	return x.x < y.x && x.y < y.y
+}
+
+pub fn (a Foo) + (b Foo) Foo {
+	return Foo{a.x + b.x, a.y + b.y}
+}
+
+fn main() {
+	x := Foo{4.0, 3.0}
+	y := Foo{1.0, 2.0}
+	println(x + y)
+	println(Foo{42.42, 0.0} == Foo{0.0, 42.42})
+	println(x > y)
+}