Security/forbid halt

README.md

@@ -42,6 +42,7 @@ The following customizations have been made to adapt the original `ichiban/prolo
 - Removed support for trigonometric functions (`sin`, `cos`, `tan`, `asin`, `acos`, `atan`).
 - Introduced VM hooks for enhanced Prolog execution control.
 - Added support for the `Dict` term.
+- `halt/0` and `halt/1` are forbidden and will throw an error.
 
 ## License
 

engine/builtin.go

@@ -1960,7 +1960,9 @@ func PeekChar(vm *VM, streamOrAlias, char Term, k Cont, env *Env) *Promise {
 	}
 }
 
-var osExit = os.Exit
+var osExit = func(_ int) {
+	panic("halt/1 is not allowed")
+}
 
 // Halt exits the process with exit code of n.
 func Halt(_ *VM, n Term, k Cont, env *Env) *Promise {

engine/builtin_test.go

@@ -37,6 +37,12 @@ func TestCall(t *testing.T) {
 	vm.Register0(NewAtom("do_not_call_wrapped"), func(*VM, Cont, *Env) *Promise {
 		panic(errors.New("told you"))
 	})
+	vm.Register0(NewAtom("do_not_call_exception"), func(*VM, Cont, *Env) *Promise {
+		panic(Exception{NewAtom("error").Apply(NewAtom("panic_error").Apply(NewAtom("told you")))})
+	})
+	vm.Register0(NewAtom("do_not_call_misc_error"), func(*VM, Cont, *Env) *Promise {
+		panic(42)
+	})
 	assert.NoError(t, vm.Compile(context.Background(), `
 foo.
 foo(_, _).
@@ -64,9 +70,11 @@ f(g([a, [b, c|X], Y{x:5}])).
 
 		{title: `cover all`, goal: atomComma.Apply(atomCut, NewAtom("f").Apply(NewAtom("g").Apply(List(NewAtom("a"), PartialList(NewVariable(), NewAtom("b"), NewAtom("c")), makeDict(NewAtom("foo"), NewAtom("x"), Integer(5)))))), ok: true},
 		{title: `out of memory`, goal: NewAtom("foo").Apply(NewVariable(), NewVariable(), NewVariable(), NewVariable(), NewVariable(), NewVariable(), NewVariable(), NewVariable(), NewVariable()), err: resourceError(resourceMemory, nil), mem: 1},
-		{title: `panic`, goal: NewAtom("do_not_call"), err: PanicError{errors.New("told you")}},
-		{title: `panic (lazy)`, goal: NewAtom("lazy_do_not_call"), err: PanicError{errors.New("told you")}},
-		{title: `panic (wrapped)`, goal: NewAtom("do_not_call_wrapped"), err: PanicError{errors.New("told you")}},
+		{title: `panic`, goal: NewAtom("do_not_call"), err: Exception{NewAtom("error").Apply(NewAtom("panic_error").Apply(NewAtom("told you")))}},
+		{title: `panic (lazy)`, goal: NewAtom("lazy_do_not_call"), err: Exception{NewAtom("error").Apply(NewAtom("panic_error").Apply(NewAtom("told you")))}},
+		{title: `panic (wrapped)`, goal: NewAtom("do_not_call_wrapped"), err: Exception{NewAtom("error").Apply(NewAtom("panic_error").Apply(NewAtom("told you")))}},
+		{title: `panic (exception)`, goal: NewAtom("do_not_call_exception"), err: Exception{NewAtom("error").Apply(NewAtom("panic_error").Apply(NewAtom("told you")))}},
+		{title: `panic (misc)`, goal: NewAtom("do_not_call_misc_error"), err: Exception{NewAtom("error").Apply(NewAtom("panic_error").Apply(NewAtom("42")))}},
 	}
 
 	for _, tt := range tests {
@@ -5519,20 +5527,11 @@ func TestPeekChar(t *testing.T) {
 
 func Test_Halt(t *testing.T) {
 	t.Run("ok", func(t *testing.T) {
-		var exitCalled bool
-		osExit = func(code int) {
-			assert.Equal(t, 2, code)
-			exitCalled = true
-		}
-		defer func() {
-			osExit = os.Exit
-		}()
-
-		ok, err := Halt(nil, Integer(2), Success, nil).Force(context.Background())
-		assert.NoError(t, err)
-		assert.True(t, ok)
-
-		assert.True(t, exitCalled)
+		ok, err := Delay(func(ctx context.Context) *Promise {
+			return Halt(nil, Integer(2), Success, nil)
+		}).Force(context.Background())
+		assert.EqualError(t, err, "error(panic_error(halt/1 is not allowed))")
+		assert.False(t, ok)
 	})
 
 	t.Run("n is a variable", func(t *testing.T) {

engine/promise.go

@@ -162,10 +162,12 @@ func ensurePromise(p **Promise) {
 
 func panicError(r interface{}) error {
 	switch r := r.(type) {
+	case Exception:
+		return r
 	case error:
-		return PanicError{r}
+		return Exception{term: atomError.Apply(NewAtom("panic_error").Apply(NewAtom(r.Error())))}
 	default:
-		return PanicError{fmt.Errorf("%v", r)}
+		return Exception{term: atomError.Apply(NewAtom("panic_error").Apply(NewAtom(fmt.Sprintf("%v", r))))}
 	}
 }