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Add *State.XMove method
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Same signature as `lua_xmove`,
but permits moving between unrelated states
if the values are frozen.
If we support coroutines later,
we can relax the restriction between related states.

Updates #75
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@zombiezen
zombiezen committed Feb 17, 2025
1 parent d5b3027 commit f42fff7
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Showing 2 changed files with 209 additions and 0 deletions.
38 changes: 38 additions & 0 deletions internal/lua/lua.go
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Original file line number Diff line number Diff line change
Expand Up @@ -394,6 +394,44 @@ func (l *State) grow(wantTop int) bool {
return true
}

// XMove exchanges values between states:
// n values are popped from src,
// then pushed onto the stack of l.
// If l and src are different states
// and the top n values of src's stack are not frozen using [*State.Freeze],
// then XMove returns an error.
func (l *State) XMove(src *State, n int) error {
if n < 0 {
return errors.New("negative count to move")
}
if n == 0 {
return nil
}
if src.Top() < n {
return errMissingArguments
}
if src == l {
// No-op on same state.
return nil
}

src.init()
l.init()
if len(l.stack)+n > cap(l.stack) {
return errStackOverflow
}
newTop := len(src.stack) - n
elems := src.stack[newTop:]
for _, v := range elems {
if !isFrozen(v) {
return errors.New("moving unfrozen values between independent states")
}
}
l.stack = append(l.stack, elems...)
src.setTop(newTop)
return nil
}

// IsNumber reports if the value at the given index is a number
// or a string convertible to a number.
func (l *State) IsNumber(idx int) bool {
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171 changes: 171 additions & 0 deletions internal/lua/lua_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1546,6 +1546,177 @@ func TestFreeze(t *testing.T) {
})
}

func TestXMove(t *testing.T) {
t.Run("SameState", func(t *testing.T) {
state := new(State)
defer func() {
if err := state.Close(); err != nil {
t.Error("state1.Close:", err)
}
}()

state.PushInteger(555)
state.PushInteger(123)
state.CreateTable(2, 0)
tableID := state.ID(-1)
state.PushInteger(456)
if err := state.RawSetIndex(-2, 1); err != nil {
t.Fatal("t[1] = 456 raised", err)
}
state.PushInteger(789)
if err := state.RawSetIndex(-2, 2); err != nil {
t.Fatal("t[2] = 789 raised", err)
}
if got, want := state.Top(), 3; got != want {
t.Errorf("before XMove, state.Top() = %d; want %d", got, want)
}

if err := state.XMove(state, 2); err != nil {
t.Error("XMove:", err)
}

if got, want := state.Top(), 3; got != want {
t.Errorf("after XMove, state.Top() = %d; want %d", got, want)
}
if got, err := valueToGo(state, 1); err != nil {
t.Errorf("after XMove, state.stack[1] %v", err)
} else if want := int64(555); !cmp.Equal(got, want) {
t.Errorf("after XMove, state.stack[1] = %v; want %v", got, want)
}
if got, err := valueToGo(state, 2); err != nil {
t.Errorf("after XMove, state.stack[2] %v", err)
} else if want := int64(123); !cmp.Equal(got, want) {
t.Errorf("after XMove, state.stack[2] = %v; want %v", got, want)
}
if got, want := state.Type(3), TypeTable; got != want {
t.Errorf("after XMove, state.Type(3) = %v; want %v", got, want)
} else if got, want := state.ID(3), tableID; got != want {
t.Errorf("after XMove, state.ID(3) = %d; want %d", got, want)
}
})

t.Run("DifferentStates", func(t *testing.T) {
state1 := new(State)
state2 := new(State)
defer func() {
if err := state1.Close(); err != nil {
t.Error("state1.Close:", err)
}
if err := state2.Close(); err != nil {
t.Error("state2.Close:", err)
}
}()

state1.PushInteger(555)
state1.PushInteger(123)
state1.CreateTable(2, 0)
tableID := state1.ID(-1)
state1.PushInteger(456)
if err := state1.RawSetIndex(-2, 1); err != nil {
t.Fatal("t[1] = 456 raised", err)
}
state1.PushInteger(789)
if err := state1.RawSetIndex(-2, 2); err != nil {
t.Fatal("t[2] = 789 raised", err)
}
if err := state1.Freeze(-1); err != nil {
t.Fatal(err)
}
if got, want := state1.Top(), 3; got != want {
t.Errorf("before XMove, state1.Top() = %d; want %d", got, want)
}
if got, want := state2.Top(), 0; got != want {
t.Errorf("before XMove, state2.Top() = %d; want %d", got, want)
}

if err := state2.XMove(state1, 2); err != nil {
t.Error("XMove:", err)
}

if got, want := state1.Top(), 1; got != want {
t.Errorf("after XMove, state1.Top() = %d; want %d", got, want)
}
if got, err := valueToGo(state1, 1); err != nil {
t.Errorf("after XMove, state1.stack[1] %v", err)
} else if want := int64(555); !cmp.Equal(got, want) {
t.Errorf("after XMove, state1.stack[1] = %v; want %v", got, want)
}

if got, want := state2.Top(), 2; got != want {
t.Errorf("after XMove, state2.Top() = %d; want %d", got, want)
}
if got, err := valueToGo(state2, 1); err != nil {
t.Errorf("after XMove, state2.stack[1] %v", err)
} else if want := int64(123); !cmp.Equal(got, want) {
t.Errorf("after XMove, state2.stack[1] = %v; want %v", got, want)
}
if got, want := state2.Type(2), TypeTable; got != want {
t.Errorf("after XMove, state2.Type(2) = %v; want %v", got, want)
} else if got, want := state2.ID(2), tableID; got != want {
t.Errorf("after XMove, state2.ID(2) = %d; want %d", got, want)
}
})

t.Run("DifferentStatesWithoutFreeze", func(t *testing.T) {
state1 := new(State)
state2 := new(State)
defer func() {
if err := state1.Close(); err != nil {
t.Error("state1.Close:", err)
}
if err := state2.Close(); err != nil {
t.Error("state2.Close:", err)
}
}()

state1.PushInteger(555)
state1.PushInteger(123)
state1.CreateTable(2, 0)
tableID := state1.ID(-1)
state1.PushInteger(456)
if err := state1.RawSetIndex(-2, 1); err != nil {
t.Fatal("t[1] = 456 raised", err)
}
state1.PushInteger(789)
if err := state1.RawSetIndex(-2, 2); err != nil {
t.Fatal("t[2] = 789 raised", err)
}
if got, want := state1.Top(), 3; got != want {
t.Errorf("before XMove, state1.Top() = %d; want %d", got, want)
}
if got, want := state2.Top(), 0; got != want {
t.Errorf("before XMove, state2.Top() = %d; want %d", got, want)
}

if err := state2.XMove(state1, 2); err == nil {
t.Error("XMove did not return an error")
}

if got, want := state1.Top(), 3; got != want {
t.Errorf("after XMove, state1.Top() = %d; want %d", got, want)
}
if got, err := valueToGo(state1, 1); err != nil {
t.Errorf("after XMove, state1.stack[1] %v", err)
} else if want := int64(555); !cmp.Equal(got, want) {
t.Errorf("after XMove, state1.stack[1] = %v; want %v", got, want)
}
if got, err := valueToGo(state1, 2); err != nil {
t.Errorf("after XMove, state1.stack[2] %v", err)
} else if want := int64(123); !cmp.Equal(got, want) {
t.Errorf("after XMove, state1.stack[2] = %v; want %v", got, want)
}
if got, want := state1.Type(3), TypeTable; got != want {
t.Errorf("after XMove, state1.Type(3) = %v; want %v", got, want)
} else if got, want := state1.ID(3), tableID; got != want {
t.Errorf("after XMove, state1.ID(3) = %d; want %d", got, want)
}

if got, want := state2.Top(), 0; got != want {
t.Errorf("after XMove, state2.Top() = %d; want %d", got, want)
}
})
}

func TestRotate(t *testing.T) {
tests := []struct {
s []int
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