errcount: factor errcount abstraction from operations

fs/operations/operations.go

@@ -35,6 +35,7 @@ import (
 	"github.com/rclone/rclone/fs/object"
 	"github.com/rclone/rclone/fs/walk"
 	"github.com/rclone/rclone/lib/atexit"
+	"github.com/rclone/rclone/lib/errcount"
 	"github.com/rclone/rclone/lib/random"
 	"github.com/rclone/rclone/lib/readers"
 	"golang.org/x/sync/errgroup"
@@ -1353,9 +1354,7 @@ func Rmdirs(ctx context.Context, f fs.Fs, dir string, leaveRoot bool) error {
 	}
 
 	var (
-		errMu     sync.Mutex
-		errCount  int
-		lastError error
+		errCount = errcount.New()
 	)
 	// Delete all directories at the same level in parallel
 	for level := len(toDelete) - 1; level >= 0; level-- {
@@ -1378,10 +1377,7 @@ func Rmdirs(ctx context.Context, f fs.Fs, dir string, leaveRoot bool) error {
 				if err != nil {
 					err = fs.CountError(err)
 					fs.Errorf(dir, "Failed to rmdir: %v", err)
-					errMu.Lock()
-					lastError = err
-					errCount += 1
-					errMu.Unlock()
+					errCount.Add(err)
 				}
 				return nil // don't return errors, just count them
 			})
@@ -1391,10 +1387,7 @@ func Rmdirs(ctx context.Context, f fs.Fs, dir string, leaveRoot bool) error {
 			return err
 		}
 	}
-	if lastError != nil {
-		return fmt.Errorf("failed to remove %d directories: last error: %w", errCount, lastError)
-	}
-	return nil
+	return errCount.Err("failed to remove directories")
 }
 
 // GetCompareDest sets up --compare-dest

lib/errcount/errcount.go

@@ -0,0 +1,58 @@
+// Package errcount provides an easy to use error counter which
+// returns error count and last error so as to not overwhelm the user
+// with errors.
+package errcount
+
+import (
+	"fmt"
+	"sync"
+)
+
+// ErrCount stores the state of the error counter.
+type ErrCount struct {
+	mu      sync.Mutex
+	lastErr error
+	count   int
+}
+
+// New makes a new error counter
+func New() *ErrCount {
+	return new(ErrCount)
+}
+
+// Add an error to the error count.
+//
+// err may be nil.
+//
+// Thread safe.
+func (ec *ErrCount) Add(err error) {
+	if err == nil {
+		return
+	}
+	ec.mu.Lock()
+	ec.count++
+	ec.lastErr = err
+	ec.mu.Unlock()
+}
+
+// Err returns the error summary so far - may be nil
+//
+// txt is put in front of the error summary
+//
+//	txt: %d errors: last error: %w
+//
+// or this if only one error
+//
+//	txt: %w
+//
+// Thread safe.
+func (ec *ErrCount) Err(txt string) error {
+	ec.mu.Lock()
+	defer ec.mu.Unlock()
+	if ec.count == 0 {
+		return nil
+	} else if ec.count == 1 {
+		return fmt.Errorf("%s: %w", txt, ec.lastErr)
+	}
+	return fmt.Errorf("%s: %d errors: last error: %w", txt, ec.count, ec.lastErr)
+}

lib/errcount/errcount_test.go

@@ -0,0 +1,27 @@
+package errcount
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestErrCount(t *testing.T) {
+	ec := New()
+	assert.Equal(t, nil, ec.Err("none"))
+
+	e1 := errors.New("one")
+	ec.Add(e1)
+
+	err := ec.Err("stuff")
+	assert.True(t, errors.Is(err, e1), err)
+	assert.Equal(t, "stuff: one", err.Error())
+
+	e2 := errors.New("two")
+	ec.Add(e2)
+
+	err = ec.Err("stuff")
+	assert.True(t, errors.Is(err, e2), err)
+	assert.Equal(t, "stuff: 2 errors: last error: two", err.Error())
+}