feat: register.AtMostOnce.Temp{Override,Clear}() methods

Author: ARR4N

libevm/register/register.go

@@ -1,4 +1,4 @@
-// Copyright 2024 the libevm authors.
+// Copyright 2024-2025 the libevm authors.
 //
 // The libevm additions to go-ethereum are free software: you can redistribute
 // them and/or modify them under the terms of the GNU Lesser General Public License
@@ -66,3 +66,28 @@ func (o *AtMostOnce[T]) TestOnlyClear() {
 		o.v = nil
 	})
 }
+
+// TempOverride calls `fn`, overriding any registered `T`, but only for the life
+// of the call.
+//
+// It is valid to call this method with or without a prior call to
+// [AtMostOnce.Register].
+func (o *AtMostOnce[T]) TempOverride(with T, fn func()) {
+	o.temp(&with, fn)
+}
+
+// TempClear calls `fn`, clearing any registered `T`, but only for the life of
+// the call.
+//
+// It is valid to call this method with or without a prior call to
+// [AtMostOnce.Register].
+func (o *AtMostOnce[T]) TempClear(fn func()) {
+	o.temp(nil, fn)
+}
+
+func (o *AtMostOnce[T]) temp(with *T, fn func()) {
+	old := o.v
+	o.v = with
+	fn()
+	o.v = old
+}

libevm/register/register_test.go

@@ -0,0 +1,78 @@
+// Copyright 2025 the libevm authors.
+//
+// The libevm additions to go-ethereum are free software: you can redistribute
+// them and/or modify them under the terms of the GNU Lesser General Public License
+// as published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The libevm additions are distributed in the hope that they will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package register
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestAtMostOnce(t *testing.T) {
+	var sut AtMostOnce[int]
+	assertRegistered := func(t *testing.T, want int) {
+		t.Helper()
+		require.True(t, sut.Registered(), "Registered()")
+		assert.Equal(t, want, sut.Get(), "Get()")
+	}
+
+	const val int = 42
+	require.NoError(t, sut.Register(val), "Register()")
+	assertRegistered(t, val)
+
+	assert.PanicsWithValue(
+		t, ErrReRegistration,
+		func() { sut.MustRegister(0) },
+		"MustRegister() after Register()",
+	)
+
+	t.Run("TestOnlyClear", func(t *testing.T) {
+		sut.TestOnlyClear()
+		require.False(t, sut.Registered(), "Registered()")
+
+		t.Run("re-registration", func(t *testing.T) {
+			sut.MustRegister(val)
+			assertRegistered(t, val)
+		})
+	})
+	if t.Failed() {
+		return
+	}
+
+	t.Run("TempOverride", func(t *testing.T) {
+		t.Run("during", func(t *testing.T) {
+			sut.TempOverride(val+1, func() {
+				assertRegistered(t, val+1)
+			})
+		})
+		t.Run("after", func(t *testing.T) {
+			assertRegistered(t, val)
+		})
+	})
+
+	t.Run("TempClear", func(t *testing.T) {
+		t.Run("during", func(t *testing.T) {
+			sut.TempClear(func() {
+				assert.False(t, sut.Registered(), "Registered()")
+			})
+		})
+		t.Run("after", func(t *testing.T) {
+			assertRegistered(t, val)
+		})
+	})
+}