eval: add missing identity cast implementations

This adds missing identity casts for the ltree and void types. Identity
casts are usually elided by the optimizer, but LDR random schema tests
were flaking on schemas that involve these types.

Release note: none
Epic: CRDB-48647

Author: jeffswenson

pkg/sql/sem/eval/BUILD.bazel

@@ -116,6 +116,7 @@ go_test(
     name = "eval_test",
     srcs = [
         "cast_map_test.go",
+        "cast_rand_test.go",
         "cast_test.go",
         "compare_test.go",
         "eval_internal_test.go",

pkg/sql/sem/eval/cast.go

@@ -961,6 +961,8 @@ func performCastWithoutPrecisionTruncation(
 		}
 	case types.LTreeFamily:
 		switch v := d.(type) {
+		case *tree.DLTree:
+			return d, nil
 		case *tree.DString:
 			ltree, err := tree.ParseDLTree(string(*v))
 			if err != nil {
@@ -1051,7 +1053,7 @@ func performCastWithoutPrecisionTruncation(
 		}
 	case types.VoidFamily:
 		switch d.(type) {
-		case *tree.DString, *tree.DCollatedString:
+		case *tree.DString, *tree.DCollatedString, *tree.DVoid:
 			return tree.DVoidDatum, nil
 		}
 	}

pkg/sql/sem/eval/cast_rand_test.go

@@ -0,0 +1,76 @@
+// Copyright 2025 The Cockroach Authors.
+//
+// Use of this software is governed by the CockroachDB Software License
+// included in the /LICENSE file.
+
+package eval_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/cockroachdb/cockroach/pkg/settings/cluster"
+	"github.com/cockroachdb/cockroach/pkg/sql/randgen"
+	"github.com/cockroachdb/cockroach/pkg/sql/sem/eval"
+	"github.com/cockroachdb/cockroach/pkg/sql/types"
+	"github.com/cockroachdb/cockroach/pkg/util/leaktest"
+	"github.com/cockroachdb/cockroach/pkg/util/log"
+	"github.com/cockroachdb/cockroach/pkg/util/randutil"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCastIdentityRandom(t *testing.T) {
+	defer leaktest.AfterTest(t)()
+	defer log.Scope(t).Close(t)
+
+	var usesFamily func(typ *types.T, family types.Family) bool
+	usesFamily = func(typ *types.T, family types.Family) bool {
+		switch typ.Family() {
+		case family:
+			return true
+		case types.ArrayFamily:
+			return usesFamily(typ.ArrayContents(), family)
+		case types.TupleFamily:
+			for _, tupleType := range typ.TupleContents() {
+				if usesFamily(tupleType, family) {
+					return true
+				}
+			}
+			return false
+		default:
+			return false
+		}
+	}
+
+	ctx := context.Background()
+	castCtx := eval.MakeTestingEvalContext(cluster.MakeTestingClusterSettings())
+	rng, _ := randutil.NewTestRand()
+	for trial := 0; trial < 100; trial++ {
+		typ := randgen.RandType(rng)
+
+		// Test eval context does not support the OidFamily
+		if usesFamily(typ, types.OidFamily) {
+			continue
+		}
+
+		value := randgen.RandDatum(rng, typ, true /* nullOk */)
+
+		// A value should cast to its own type and be equal to itself after the
+		// cast.
+		identityCastValue, err := eval.PerformCast(ctx, &castCtx, value, typ)
+		require.NoError(t, err)
+
+		cmp, err := value.Compare(ctx, &castCtx, identityCastValue)
+		require.NoError(t, err)
+		require.Zero(t, cmp)
+
+		// A value should cast to its canonical type and be equal to itself after
+		// the cast.
+		canonicalCastValue, err := eval.PerformCast(ctx, &castCtx, value, typ.Canonical())
+		require.NoError(t, err)
+
+		cmp, err = value.Compare(ctx, &castCtx, canonicalCastValue)
+		require.NoError(t, err)
+		require.Zero(t, cmp)
+	}
+}