ui/backup: Replace channels with a mutex

The channel-based algorithm had grown quite complicated. This is easier
to reason about and likely to be more performant with very many
CompleteBlob calls.

internal/ui/backup/progress_test.go

@@ -0,0 +1,87 @@
+package backup
+
+import (
+	"context"
+	"io"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/restic/restic/internal/archiver"
+	"github.com/restic/restic/internal/restic"
+)
+
+type mockPrinter struct {
+	sync.Mutex
+	dirUnchanged, fileNew bool
+	id                    restic.ID
+}
+
+func (p *mockPrinter) Update(total, processed Counter, errors uint, currentFiles map[string]struct{}, start time.Time, secs uint64) {
+}
+func (p *mockPrinter) Error(item string, err error) error        { return err }
+func (p *mockPrinter) ScannerError(item string, err error) error { return err }
+
+func (p *mockPrinter) CompleteItem(messageType string, item string, previous, current *restic.Node, s archiver.ItemStats, d time.Duration) {
+	p.Lock()
+	defer p.Unlock()
+
+	switch messageType {
+	case "dir unchanged":
+		p.dirUnchanged = true
+	case "file new":
+		p.fileNew = true
+	}
+}
+
+func (p *mockPrinter) ReportTotal(_ string, _ time.Time, _ archiver.ScanStats) {}
+func (p *mockPrinter) Finish(id restic.ID, _ time.Time, summary *Summary, dryRun bool) {
+	p.Lock()
+	defer p.Unlock()
+
+	_ = *summary // Should not be nil.
+	p.id = id
+}
+
+func (p *mockPrinter) Reset() {}
+
+func (p *mockPrinter) Stdout() io.WriteCloser { return nil }
+func (p *mockPrinter) Stderr() io.WriteCloser { return nil }
+
+func (p *mockPrinter) P(msg string, args ...interface{}) {}
+func (p *mockPrinter) V(msg string, args ...interface{}) {}
+
+func TestProgress(t *testing.T) {
+	t.Parallel()
+
+	prnt := &mockPrinter{}
+	prog := NewProgress(prnt, time.Millisecond)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	go prog.Run(ctx)
+
+	prog.StartFile("foo")
+	prog.CompleteBlob(1024)
+
+	// "dir unchanged"
+	node := restic.Node{Type: "dir"}
+	prog.CompleteItem("foo", &node, &node, archiver.ItemStats{}, 0)
+	// "file new"
+	node.Type = "file"
+	prog.CompleteItem("foo", nil, &node, archiver.ItemStats{}, 0)
+
+	time.Sleep(10 * time.Millisecond)
+	cancel()
+	id := restic.NewRandomID()
+	prog.Finish(id, false)
+
+	if !prnt.dirUnchanged {
+		t.Error(`"dir unchanged" event not seen`)
+	}
+	if !prnt.fileNew {
+		t.Error(`"file new" event not seen`)
+	}
+	if prnt.id != id {
+		t.Errorf("id not stored (has %v)", prnt.id)
+	}
+}