internal/shader: bug fix: deduction checks for the % operator were lacked

internal/shader/expr.go

@@ -202,9 +202,11 @@ func (cs *compileState) parseExpr(block *block, expr ast.Expr, markLocalVariable
 			return nil, nil, nil, false
 		}
 
+		// For `%`, both types must be deducible to integers.
 		if op == shaderir.ModOp {
 			// TODO: What about ivec?
-			if lhst.Main != shaderir.Int || rhst.Main != shaderir.Int {
+			if lhst.Main != shaderir.Int && (lhs[0].ConstType == shaderir.ConstTypeNone || !canTruncateToInteger(lhs[0].Const)) ||
+				rhst.Main != shaderir.Int && (rhs[0].ConstType == shaderir.ConstTypeNone || !canTruncateToInteger(rhs[0].Const)) {
 				var wrongType shaderir.Type
 				if lhst.Main != shaderir.Int {
 					wrongType = lhst

shader_test.go

@@ -1283,6 +1283,24 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 
 	if _, err := ebiten.NewShader([]byte(`package main
 
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	a := int(2) % 0.5
+	return vec4(a)
+}`)); err == nil {
+		t.Errorf("error must be non-nil but was nil")
+	}
+
+	if _, err := ebiten.NewShader([]byte(`package main
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	a := int(2) % 1.0
+	return vec4(a)
+}`)); err != nil {
+		t.Error(err)
+	}
+
+	if _, err := ebiten.NewShader([]byte(`package main
+
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	a := 2.0
 	b := 0.5