chore: Convert iterators in pattern module to v2.Iterator interface (#13407)

This is first follow up to #13273 

It changes the iterator from the pattern module to use the `v2.CloseIterator` to avoid re-implementing the iterator logic. With this change, the function `Error()` on the pattern iterator is renamed to `Err()` to conform with the `v2.Iterator` interface.

Signed-off-by: Christian Haudum <christian.haudum@gmail.com>

pkg/iter/iterator.go

@@ -7,11 +7,11 @@ import (
 	"github.com/grafana/loki/v3/pkg/logproto"
 )
 
-type Value interface {
+type logprotoType interface {
 	logproto.Entry | logproto.Sample
 }
 
-type StreamIterator[T Value] interface {
+type StreamIterator[T logprotoType] interface {
 	v2.CloseIterator[T]
 	// Labels returns the labels for the current entry.
 	// The labels can be mutated by the query engine and not reflect the original stream.
@@ -24,7 +24,7 @@ type EntryIterator StreamIterator[logproto.Entry]
 type SampleIterator StreamIterator[logproto.Sample]
 
 // noOpIterator implements StreamIterator
-type noOpIterator[T Value] struct{}
+type noOpIterator[T logprotoType] struct{}
 
 func (noOpIterator[T]) Next() bool         { return false }
 func (noOpIterator[T]) Err() error         { return nil }
@@ -37,7 +37,7 @@ var NoopEntryIterator = noOpIterator[logproto.Entry]{}
 var NoopSampleIterator = noOpIterator[logproto.Sample]{}
 
 // errorIterator implements StreamIterator
-type errorIterator[T Value] struct{}
+type errorIterator[T logprotoType] struct{}
 
 func (errorIterator[T]) Next() bool         { return false }
 func (errorIterator[T]) Err() error         { return errors.New("error") }

pkg/iter/v2/iter.go

@@ -159,15 +159,15 @@ func NewCancelableIter[T any](ctx context.Context, itr Iterator[T]) *Cancellable
 	return &CancellableIter[T]{ctx: ctx, Iterator: itr}
 }
 
-func NewCloseableIterator[T io.Closer](itr Iterator[T]) *CloseIter[T] {
-	return &CloseIter[T]{itr}
+func NewCloserIter[T io.Closer](itr Iterator[T]) *CloserIter[T] {
+	return &CloserIter[T]{itr}
 }
 
-type CloseIter[T io.Closer] struct {
+type CloserIter[T io.Closer] struct {
 	Iterator[T]
 }
 
-func (i *CloseIter[T]) Close() error {
+func (i *CloserIter[T]) Close() error {
 	return i.At().Close()
 }
 
@@ -226,3 +226,22 @@ func (it *CounterIter[T]) Next() bool {
 func (it *CounterIter[T]) Count() int {
 	return it.count
 }
+
+func WithClose[T any](itr Iterator[T], close func() bool) *CloseIter[T] {
+	return &CloseIter[T]{
+		Iterator: itr,
+		close:    close,
+	}
+}
+
+type CloseIter[T any] struct {
+	Iterator[T]
+	close func() bool
+}
+
+func (i *CloseIter[T]) Close() error {
+	if i.close != nil {
+		return i.Close()
+	}
+	return nil
+}

pkg/pattern/iter/batch.go

@@ -31,7 +31,7 @@ func ReadBatch(it Iterator, batchSize int) (*logproto.QueryPatternsResponse, err
 			Samples: samples,
 		})
 	}
-	return &result, it.Error()
+	return &result, it.Err()
 }
 
 func ReadAll(it Iterator) (*logproto.QueryPatternsResponse, error) {

pkg/pattern/iter/iterator.go

@@ -1,82 +1,39 @@
 package iter
 
 import (
+	iter "github.com/grafana/loki/v3/pkg/iter/v2"
 	"github.com/grafana/loki/v3/pkg/logproto"
 )
 
-var Empty Iterator = &emptyIterator{}
-
-// TODO(chaudum): inline v2.Iteratpr[logproto.PatternSample]
 type Iterator interface {
-	Next() bool
+	iter.CloseIterator[logproto.PatternSample]
 
 	Pattern() string
-	At() logproto.PatternSample
-
-	Error() error
-	Close() error
 }
 
-func NewSlice(pattern string, s []logproto.PatternSample) Iterator {
-	// TODO(chaudum): replace with v2.NewSliceIter()
-	return &sliceIterator{
-		values:  s,
-		pattern: pattern,
-		i:       -1,
+func NewSlice(pattern string, s []logproto.PatternSample) *PatternIter {
+	return &PatternIter{
+		CloseIterator: iter.WithClose(iter.NewSliceIter(s), nil),
+		pattern:       pattern,
 	}
 }
 
-type sliceIterator struct {
-	i       int
+func NewEmpty(pattern string) *PatternIter {
+	return &PatternIter{
+		CloseIterator: iter.WithClose(iter.NewEmptyIter[logproto.PatternSample](), nil),
+		pattern:       pattern,
+	}
+}
+
+type PatternIter struct {
+	iter.CloseIterator[logproto.PatternSample]
 	pattern string
-	values  []logproto.PatternSample
 }
 
-func (s *sliceIterator) Next() bool {
-	s.i++
-	return s.i < len(s.values)
-}
-
-func (s *sliceIterator) Pattern() string {
+func (s *PatternIter) Pattern() string {
 	return s.pattern
 }
 
-func (s *sliceIterator) At() logproto.PatternSample {
-	return s.values[s.i]
-}
-
-func (s *sliceIterator) Error() error {
-	return nil
-}
-
-func (s *sliceIterator) Close() error {
-	return nil
-}
-
-type emptyIterator struct {
-	pattern string
-}
-
-func (e *emptyIterator) Next() bool {
-	return false
-}
-
-func (e *emptyIterator) Pattern() string {
-	return e.pattern
-}
-
-func (e *emptyIterator) At() logproto.PatternSample {
-	return logproto.PatternSample{}
-}
-
-func (e *emptyIterator) Error() error {
-	return nil
-}
-
-func (e *emptyIterator) Close() error {
-	return nil
-}
-
 type nonOverlappingIterator struct {
 	iterators []Iterator
 	curr      Iterator
@@ -116,11 +73,11 @@ func (i *nonOverlappingIterator) Pattern() string {
 	return i.pattern
 }
 
-func (i *nonOverlappingIterator) Error() error {
-	if i.curr == nil {
-		return nil
+func (i *nonOverlappingIterator) Err() error {
+	if i.curr != nil {
+		return i.curr.Err()
 	}
-	return i.curr.Error()
+	return nil
 }
 
 func (i *nonOverlappingIterator) Close() error {

pkg/pattern/iter/iterator_test.go

@@ -65,8 +65,8 @@ func slice(it Iterator) []patternSample {
 			sample:  it.At(),
 		})
 	}
-	if it.Error() != nil {
-		panic(it.Error())
+	if it.Err() != nil {
+		panic(it.Err())
 	}
 	return samples
 }

pkg/pattern/iter/merge_pattern.go

@@ -78,7 +78,7 @@ func (m *mergeIterator) At() logproto.PatternSample {
 	return m.current.sample
 }
 
-func (m *mergeIterator) Error() error {
+func (m *mergeIterator) Err() error {
 	return nil
 }
 

pkg/pattern/iter/query_client.go

@@ -47,7 +47,7 @@ func (i *queryClientIterator) At() logproto.PatternSample {
 	return i.curr.At()
 }
 
-func (i *queryClientIterator) Error() error {
+func (i *queryClientIterator) Err() error {
 	return i.err
 }