Add from.DirWalk

from/from.go

@@ -3,6 +3,8 @@ package from
 import (
 	"bufio"
 	"context"
+	"errors"
+	"io/fs"
 	"iter"
 )
 
@@ -39,3 +41,24 @@ func Chan[T any](ctx context.Context, src <-chan T) iter.Seq[T] {
 		}
 	}
 }
+
+// DirStep represents a step in a directory Walk.
+type DirStep struct {
+	FullPath string
+	Entry    fs.DirEntry
+}
+
+// DirWalk emits all entries for root and its subdirectories.
+// Errors are forwarded, and the consumer may decide wether to stop iteration or continue consuming further values.
+//
+// Use os.DirFS(path) to create fsys from disk.
+func DirWalk(ctx context.Context, fsys fs.FS, root string) iter.Seq2[DirStep, error] {
+	return func(yield func(DirStep, error) bool) {
+		fs.WalkDir(fsys, root, func(path string, d fs.DirEntry, err error) error {
+			if !yield(DirStep{FullPath: path, Entry: d}, err) {
+				return errors.New("consumer stopped")
+			}
+			return nil
+		})
+	}
+}

from/from_test.go

@@ -3,9 +3,11 @@ package from_test
 import (
 	"bufio"
 	"context"
+	"io/fs"
 	"slices"
 	"strings"
 	"testing"
+	"testing/fstest"
 
 	"github.com/empijei/itertools/from"
 	"github.com/google/go-cmp/cmp"
@@ -63,3 +65,28 @@ func TestChan(t *testing.T) {
 		}
 	})
 }
+
+func TestDirWalk(t *testing.T) {
+	fsys := fstest.MapFS(map[string]*fstest.MapFile{
+		"root/foo/bar.txt": {Data: []byte("hello bar")},
+		"root/empty":       {Mode: fs.ModeDir},
+		"root/cat.txt":     {Data: []byte("hello cat")},
+	})
+
+	var errs []error
+	var dirs []string
+	from.DirWalk(context.Background(), fsys, "root")(func(ds from.DirStep, err error) bool {
+		if err != nil {
+			errs = append(errs, err)
+		}
+		dirs = append(dirs, ds.FullPath)
+		return true
+	})
+	want := []string{"root", "root/cat.txt", "root/empty", "root/foo", "root/foo/bar.txt"}
+	if diff := cmp.Diff(want, dirs); diff != "" {
+		t.Errorf("DirWalk: got %v want %v diff:\n%s", dirs, want, diff)
+	}
+	if len(errs) != 0 {
+		t.Errorf("DirWalk errors: got %v want none", errs)
+	}
+}