fix(copystructure): handle nil interfaces and reject unexported struct fields

copyValue panicked in two more places when given values that are not
plain YAML data:

- a struct field or pointer element holding a nil interface hit
  'reflect: call of reflect.Value.Set on zero Value', because
  reflect.ValueOf(nil) returns a zero Value that cannot be set.
- a struct with unexported fields, such as time.Time, hit
  'reflect.Value.Interface: cannot return value obtained from
  unexported field or method'.

Both are reachable from the SDK through CoalesceValues and
action.Install/Upgrade, and crash the calling process.

Nil interfaces are now stored as the zero value of the destination,
matching the slice fix in #31751. Structs with unexported fields now
return an "unsupported type" error, like the existing default case,
since Helm only needs to deep copy POD values.

Closes #32711

Signed-off-by: Nitin Kumar <nitinraj844126@gmail.com>

internal/copystructure/copystructure.go

@@ -80,7 +80,7 @@ func copyValue(original reflect.Value) (any, error) {
 			return nil, err
 		}
 		ptr := reflect.New(original.Type().Elem())
-		ptr.Elem().Set(reflect.ValueOf(copied))
+		setValue(ptr.Elem(), copied)
 		return ptr.Interface(), nil
 
 	case reflect.Slice:
@@ -106,13 +106,20 @@ func copyValue(original reflect.Value) (any, error) {
 		return copied.Interface(), nil
 
 	case reflect.Struct:
-		copied := reflect.New(original.Type()).Elem()
+		t := original.Type()
+		for field := range t.Fields() {
+			// Unexported fields can't be read or set through reflection.
+			if !field.IsExported() {
+				return nil, fmt.Errorf("unsupported type %v: struct with unexported fields", t)
+			}
+		}
+		copied := reflect.New(t).Elem()
 		for i := 0; i < original.NumField(); i++ {
 			elem, err := copyValue(original.Field(i))
 			if err != nil {
 				return nil, err
 			}
-			copied.Field(i).Set(reflect.ValueOf(elem))
+			setValue(copied.Field(i), elem)
 		}
 		return copied.Interface(), nil
 
@@ -126,3 +133,13 @@ func copyValue(original reflect.Value) (any, error) {
 		return original.Interface(), fmt.Errorf("unsupported type %v", original)
 	}
 }
+
+// setValue sets dst to v. A nil v (the copy of a nil interface) is stored as
+// the zero value of dst's type, since reflect.ValueOf(nil) can't be passed to Set.
+func setValue(dst reflect.Value, v any) {
+	if v == nil {
+		dst.Set(reflect.Zero(dst.Type()))
+		return
+	}
+	dst.Set(reflect.ValueOf(v))
+}

internal/copystructure/copystructure_test.go

@@ -18,6 +18,7 @@ package copystructure
 
 import (
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -193,6 +194,7 @@ func TestCopy_Map(t *testing.T) {
 }
 
 func TestCopy_Struct(t *testing.T) {
+	t.Run("exported fields", func(t *testing.T) {
 		type TestStruct struct {
 			Name     string
 			Age      int
@@ -224,6 +226,35 @@ func TestCopy_Struct(t *testing.T) {
 		input.Scores[0] = 999
 		assert.Equal(t, "John", resultStruct.Name)
 		assert.Equal(t, 95, resultStruct.Scores[0])
+	})
+
+	t.Run("nil interface field", func(t *testing.T) {
+		type WithAny struct {
+			Name  string
+			Extra any
+		}
+
+		input := map[string]any{"s": WithAny{Name: "a"}}
+
+		result, err := Copy(input)
+		require.NoError(t, err)
+		assert.Equal(t, input, result)
+	})
+
+	t.Run("unexported fields", func(t *testing.T) {
+		type withUnexported struct {
+			Name   string
+			secret int
+		}
+
+		_, err := Copy(map[string]any{"s": withUnexported{Name: "a", secret: 1}})
+		require.Error(t, err)
+	})
+
+	t.Run("time.Time", func(t *testing.T) {
+		_, err := Copy(map[string]any{"t": time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)})
+		require.Error(t, err)
+	})
 }
 
 func TestCopy_Pointer(t *testing.T) {
@@ -269,6 +300,18 @@ func TestCopy_Pointer(t *testing.T) {
 		require.NoError(t, err)
 		assert.Nil(t, result)
 	})
+
+	t.Run("pointer to nil interface", func(t *testing.T) {
+		var value any
+
+		result, err := Copy(&value)
+		require.NoError(t, err)
+
+		resultPtr, ok := result.(*any)
+		require.True(t, ok)
+		assert.Nil(t, *resultPtr)
+		assert.NotSame(t, &value, resultPtr)
+	})
 }
 
 func TestCopy_Interface(t *testing.T) {

pkg/action/install_test.go

@@ -329,6 +329,13 @@ func TestInstallRelease_NoName(t *testing.T) {
 	assert.ErrorContains(t, err, "no name provided")
 }
 
+func TestInstallRelease_UnsupportedValueType(t *testing.T) {
+	instAction := installAction(t)
+	vals := map[string]any{"deployedAt": time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)}
+	_, err := instAction.Run(buildChart(), vals)
+	assert.ErrorContains(t, err, "struct with unexported fields")
+}
+
 func TestInstallRelease_WithNotes(t *testing.T) {
 	is := assert.New(t)
 	req := require.New(t)