Clarify and verify option hook behavior

Author: oschwald

internal/decoder/decoder.go

@@ -18,7 +18,8 @@ type Decoder struct {
 }
 
 type decoderOptions struct {
-	// Reserved for future options
+	// Intentionally empty for now. DecoderOption callbacks are still invoked so
+	// adding options in a future release is non-breaking.
 }
 
 // DecoderOption configures a Decoder.

internal/decoder/decoder_test.go

@@ -556,12 +556,21 @@ func ExampleDecoder_PeekKind() {
 func TestDecoderOptions(t *testing.T) {
 	buffer := []byte{0x44, 't', 'e', 's', 't'} // String "test"
 	dd := NewDataDecoder(buffer)
+	optionCalled := false
+	option := func(*decoderOptions) {
+		optionCalled = true
+	}
 
-	// Test that options infrastructure works (even with no current options)
+	// Test that options infrastructure works (even with no current options).
 	decoder1 := NewDecoder(dd, 0)
 	require.NotNil(t, decoder1)
 
-	// Test that passing empty options slice works
+	// Test that passing options invokes each option callback.
+	decoderWithOption := NewDecoder(dd, 0, option)
+	require.NotNil(t, decoderWithOption)
+	require.True(t, optionCalled)
+
+	// Test that passing empty options slice works.
 	decoder2 := NewDecoder(dd, 0)
 	require.NotNil(t, decoder2)
 }

reader.go

@@ -202,7 +202,10 @@ func (m Metadata) BuildTime() time.Time {
 	return time.Unix(int64(m.BuildEpoch), 0)
 }
 
-type readerOptions struct{}
+type readerOptions struct {
+	// Intentionally empty for now. ReaderOption callbacks are still invoked so
+	// adding options in a future release is non-breaking.
+}
 
 // ReaderOption are options for [Open] and [OpenBytes].
 //

reader_test.go

@@ -68,6 +68,15 @@ func TestReaderBytes(t *testing.T) {
 	}
 }
 
+func TestOpenBytesAppliesReaderOptions(t *testing.T) {
+	optionCalled := false
+	_, err := OpenBytes(nil, func(*readerOptions) {
+		optionCalled = true
+	})
+	require.Error(t, err)
+	require.True(t, optionCalled)
+}
+
 func TestReaderLeaks(t *testing.T) {
 	collected := make(chan struct{})