internal/shader: add type checks for the builtin function step

Updates #2184

internal/shader/expr.go

@@ -430,9 +430,6 @@ func (cs *compileState) parseExpr(block *block, fname string, expr ast.Expr, mar
 					return nil, nil, nil, false
 				}
 				t = shaderir.Type{Main: shaderir.Mat4}
-			case shaderir.Step:
-				// TODO: Check arg types.
-				t = argts[1]
 			case shaderir.Smoothstep:
 				// TODO: Check arg types.
 				t = argts[2]
@@ -478,7 +475,7 @@ func (cs *compileState) parseExpr(block *block, fname string, expr ast.Expr, mar
 
 				t = argts[0]
 
-			case shaderir.Atan2, shaderir.Mod, shaderir.Min, shaderir.Max, shaderir.Distance, shaderir.Dot, shaderir.Cross, shaderir.Reflect:
+			case shaderir.Atan2, shaderir.Mod, shaderir.Min, shaderir.Max, shaderir.Step, shaderir.Distance, shaderir.Dot, shaderir.Cross, shaderir.Reflect:
 				// 2 arguments
 				if len(args) != 2 {
 					cs.addError(e.Pos(), fmt.Sprintf("number of %s's arguments must be 2 but %d", callee.BuiltinFunc, len(args)))
@@ -503,6 +500,11 @@ func (cs *compileState) parseExpr(block *block, fname string, expr ast.Expr, mar
 						cs.addError(e.Pos(), fmt.Sprintf("the second argument for %s must equal to the first argument %s or float but %s", callee.BuiltinFunc, argts[0].String(), argts[1].String()))
 						return nil, nil, nil, false
 					}
+				case shaderir.Step:
+					if !argts[0].Equal(&argts[1]) && argts[0].Main != shaderir.Float {
+						cs.addError(e.Pos(), fmt.Sprintf("the first argument for %s must equal to the second argument %s or float but %s", callee.BuiltinFunc, argts[1].String(), argts[0].String()))
+						return nil, nil, nil, false
+					}
 				case shaderir.Cross:
 					for i := range argts {
 						if argts[i].Main != shaderir.Vec3 {
@@ -516,9 +518,12 @@ func (cs *compileState) parseExpr(block *block, fname string, expr ast.Expr, mar
 						return nil, nil, nil, false
 					}
 				}
-				if callee.BuiltinFunc == shaderir.Distance || callee.BuiltinFunc == shaderir.Dot {
+				switch callee.BuiltinFunc {
+				case shaderir.Distance, shaderir.Dot:
 					t = shaderir.Type{Main: shaderir.Float}
-				} else {
+				case shaderir.Step:
+					t = argts[1]
+				default:
 					t = argts[0]
 				}
 

internal/shader/syntax_test.go

@@ -1793,6 +1793,55 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	}
 }
 
+// Issue #2184
+func TestSyntaxBuiltinFuncStepType(t *testing.T) {
+	cases := []struct {
+		stmt string
+		err  bool
+	}{
+		{stmt: "a := step(); _ = a", err: true},
+		{stmt: "a := step(1); _ = a", err: true},
+		{stmt: "a := step(false, false); _ = a", err: true},
+		{stmt: "a := step(1, 1); _ = a", err: false},
+		{stmt: "a := step(1.0, 1); _ = a", err: false},
+		{stmt: "a := step(1, 1.0); _ = a", err: false},
+		{stmt: "a := step(int(1), int(1)); _ = a", err: true},
+		{stmt: "a := step(1, vec2(1)); _ = a", err: false}, // The first argument can be a scalar.
+		{stmt: "a := step(1, vec3(1)); _ = a", err: false}, // The first argument can be a scalar.
+		{stmt: "a := step(1, vec4(1)); _ = a", err: false}, // The first argument can be a scalar.
+		{stmt: "a := step(vec2(1), 1); _ = a", err: true},
+		{stmt: "a := step(vec2(1), vec2(1)); _ = a", err: false},
+		{stmt: "a := step(vec2(1), vec3(1)); _ = a", err: true},
+		{stmt: "a := step(vec2(1), vec4(1)); _ = a", err: true},
+		{stmt: "a := step(vec3(1), 1); _ = a", err: true},
+		{stmt: "a := step(vec3(1), vec2(1)); _ = a", err: true},
+		{stmt: "a := step(vec3(1), vec3(1)); _ = a", err: false},
+		{stmt: "a := step(vec3(1), vec4(1)); _ = a", err: true},
+		{stmt: "a := step(vec4(1), 1); _ = a", err: true},
+		{stmt: "a := step(vec4(1), vec2(1)); _ = a", err: true},
+		{stmt: "a := step(vec4(1), vec3(1)); _ = a", err: true},
+		{stmt: "a := step(vec4(1), vec4(1)); _ = a", err: false},
+		{stmt: "a := step(mat2(1), mat2(1)); _ = a", err: true},
+		{stmt: "a := step(1, 1, 1); _ = a", err: true},
+	}
+
+	for _, c := range cases {
+		stmt := c.stmt
+		src := fmt.Sprintf(`package main
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	%s
+	return position
+}`, stmt)
+		_, err := compileToIR([]byte(src))
+		if err == nil && c.err {
+			t.Errorf("%s must return an error but does not", stmt)
+		} else if err != nil && !c.err {
+			t.Errorf("%s must not return nil but returned %v", stmt, err)
+		}
+	}
+}
+
 // Issue #2184
 func TestSyntaxBuiltinFuncClampType(t *testing.T) {
 	cases := []struct {