repository: Remove RunWorkers, report ctx.Err()

This removes RunWorkers, which had become mere overhead by successive
refactors. It also ensures that each former user of that function
returns any context error that occurs, so failure to complete an
operation is always reported as an error.

internal/repository/index_parallel.go

@@ -37,7 +37,7 @@ func ForAllIndexes(ctx context.Context, repo restic.Repository,
 		return repo.List(ctx, restic.IndexFile, func(id restic.ID, size int64) error {
 			select {
 			case <-ctx.Done():
-				return nil
+				return ctx.Err()
 			case ch <- FileInfo{id, size}:
 			}
 			return nil
@@ -69,9 +69,9 @@ func ForAllIndexes(ctx context.Context, repo restic.Repository,
 	}
 
 	// run workers on ch
-	wg.Go(func() error {
-		return RunWorkers(loadIndexParallelism, worker)
-	})
+	for i := 0; i < loadIndexParallelism; i++ {
+		wg.Go(worker)
+	}
 
 	return wg.Wait()
 }

internal/repository/master_index.go

@@ -365,7 +365,7 @@ func (mi *MasterIndex) Save(ctx context.Context, repo restic.Repository, packBla
 					select {
 					case ch <- newIndex:
 					case <-ctx.Done():
-						return nil
+						return ctx.Err()
 					}
 					newIndex = NewIndex()
 				}
@@ -397,10 +397,9 @@ func (mi *MasterIndex) Save(ctx context.Context, repo restic.Repository, packBla
 	}
 
 	// run workers on ch
-	wg.Go(func() error {
-		return RunWorkers(saveIndexParallelism, worker)
-	})
-
+	for i := 0; i < saveIndexParallelism; i++ {
+		wg.Go(worker)
+	}
 	err = wg.Wait()
 
 	return obsolete, err

internal/repository/repository.go

@@ -679,7 +679,7 @@ func (r *Repository) CreateIndexFromPacks(ctx context.Context, packsize map[rest
 		for id, size := range packsize {
 			select {
 			case <-ctx.Done():
-				return nil
+				return ctx.Err()
 			case ch <- FileInfo{id, size}:
 			}
 		}
@@ -705,9 +705,9 @@ func (r *Repository) CreateIndexFromPacks(ctx context.Context, packsize map[rest
 	}
 
 	// run workers on ch
-	wg.Go(func() error {
-		return RunWorkers(listPackParallelism, worker)
-	})
+	for i := 0; i < listPackParallelism; i++ {
+		wg.Go(worker)
+	}
 
 	err = wg.Wait()
 	if err != nil {

internal/repository/worker_group.go

@@ -1,18 +0,0 @@
-package repository
-
-import (
-	"golang.org/x/sync/errgroup"
-)
-
-// RunWorkers runs count instances of workerFunc using an errgroup.Group.
-// If an error occurs in one of the workers, it is returned.
-func RunWorkers(count int, workerFunc func() error) error {
-	var wg errgroup.Group
-
-	// run workers
-	for i := 0; i < count; i++ {
-		wg.Go(workerFunc)
-	}
-
-	return wg.Wait()
-}