fix(arrow): return owned field index slices

arrow/datatype_nested.go

@@ -19,6 +19,7 @@ package arrow
 import (
 	"errors"
 	"fmt"
+	"slices"
 	"strconv"
 	"strings"
 
@@ -501,9 +502,9 @@ func (t *StructType) FieldsByName(n string) ([]Field, bool) {
 	return fields, ok
 }
 
-// FieldIndices returns indices of all fields with the given name, or nil.
+// FieldIndices returns a copy of the indices of all fields with the given name, or nil.
 func (t *StructType) FieldIndices(name string) []int {
-	return t.index[name]
+	return slices.Clone(t.index[name])
 }
 
 func (t *StructType) Fingerprint() string {

arrow/datatype_nested_test.go

@@ -336,6 +336,17 @@ func TestStructField(t *testing.T) {
 	assert.Equal(t, ty.FieldIndices("f3"), []int(nil))
 }
 
+func TestStructTypeFieldIndicesReturnsCopy(t *testing.T) {
+	typeWithDuplicates := StructOf(
+		Field{Name: "id", Type: PrimitiveTypes.Int32},
+		Field{Name: "id", Type: PrimitiveTypes.Int64},
+	)
+	indices := typeWithDuplicates.FieldIndices("id")
+	indices[0] = 99
+
+	assert.Equal(t, []int{0, 1}, typeWithDuplicates.FieldIndices("id"))
+}
+
 func TestFieldEqual(t *testing.T) {
 	for _, tc := range []struct {
 		a, b Field

arrow/schema.go

@@ -232,12 +232,12 @@ func (sc *Schema) FieldsByName(n string) ([]Field, bool) {
 	return nil, false
 }
 
-// FieldIndices returns the indices of the named field or nil.
+// FieldIndices returns a copy of the indices of the named field or nil.
 func (sc *Schema) FieldIndices(n string) []int {
-	return sc.index[n]
+	return slices.Clone(sc.index[n])
 }
 
-func (sc *Schema) HasField(n string) bool { return len(sc.FieldIndices(n)) > 0 }
+func (sc *Schema) HasField(n string) bool { return len(sc.index[n]) > 0 }
 func (sc *Schema) HasMetadata() bool      { return len(sc.meta.keys) > 0 }
 
 // Equal returns whether two schema are equal.

arrow/schema_test.go

@@ -349,6 +349,19 @@ func TestSchemaFieldsByNameReturnsCopy(t *testing.T) {
 	}
 }
 
+func TestSchemaFieldIndicesReturnsCopy(t *testing.T) {
+	schema := NewSchema([]Field{
+		{Name: "id", Type: PrimitiveTypes.Int32},
+		{Name: "id", Type: PrimitiveTypes.Int64},
+	}, nil)
+	indices := schema.FieldIndices("id")
+	indices[0] = 99
+
+	if got, want := schema.FieldIndices("id"), []int{0, 1}; !reflect.DeepEqual(got, want) {
+		t.Fatalf("schema indices mutated through returned slice: got %v, want %v", got, want)
+	}
+}
+
 func TestSchemaAddField(t *testing.T) {
 	s := NewSchema([]Field{
 		{Name: "f1", Type: PrimitiveTypes.Int32},