Skip archiver.Scan before backup when --quiet is set

changelog/unreleased/issue-1160

@@ -0,0 +1,5 @@
+Enhancement: Improve backup speed by skipping the initial scan when the quiet flag is set
+
+We've improved the backup speed when the quiet flag -q or --quiet is set by skipping the initial scan which gathers information for displaying the progress bar and the ETA estimation.
+
+https://github.com/restic/restic/issues/1160

cmd/restic/cmd_backup.go

@@ -451,9 +451,12 @@ func runBackup(opts BackupOptions, gopts GlobalOptions, args []string) error {
 		return true
 	}
 
-	stat, err := archiver.Scan(target, selectFilter, newScanProgress(gopts))
-	if err != nil {
-		return err
+	var stat restic.Stat
+	if !gopts.Quiet {
+		stat, err = archiver.Scan(target, selectFilter, newScanProgress(gopts))
+		if err != nil {
+			return err
+		}
 	}
 
 	arch := archiver.New(repo)

cmd/restic/integration_test.go

@@ -1312,3 +1312,38 @@ func linkEqual(source, dest []string) bool {
 
 	return true
 }
+
+func TestQuietBackup(t *testing.T) {
+	env, cleanup := withTestEnvironment(t)
+	defer cleanup()
+
+	datafile := filepath.Join("testdata", "backup-data.tar.gz")
+	fd, err := os.Open(datafile)
+	if os.IsNotExist(errors.Cause(err)) {
+		t.Skipf("unable to find data file %q, skipping", datafile)
+		return
+	}
+	rtest.OK(t, err)
+	rtest.OK(t, fd.Close())
+
+	testRunInit(t, env.gopts)
+
+	rtest.SetupTarTestFixture(t, env.testdata, datafile)
+	opts := BackupOptions{}
+
+	env.gopts.Quiet = false
+	testRunBackup(t, []string{env.testdata}, opts, env.gopts)
+	snapshotIDs := testRunList(t, "snapshots", env.gopts)
+	rtest.Assert(t, len(snapshotIDs) == 1,
+		"expected one snapshot, got %v", snapshotIDs)
+
+	testRunCheck(t, env.gopts)
+
+	env.gopts.Quiet = true
+	testRunBackup(t, []string{env.testdata}, opts, env.gopts)
+	snapshotIDs = testRunList(t, "snapshots", env.gopts)
+	rtest.Assert(t, len(snapshotIDs) == 2,
+		"expected two snapshots, got %v", snapshotIDs)
+
+	testRunCheck(t, env.gopts)
+}

doc/manual_rest.rst

@@ -107,7 +107,9 @@ Subcommand that support showing progress information such as ``backup``,
 ``check`` and ``prune`` will do so unless the quiet flag ``-q`` or
 ``--quiet`` is set. When running from a non-interactive console progress
 reporting will be limited to once every 10 seconds to not fill your
-logs.
+logs. Use ``backup`` with the quiet flag ``-q`` or ``--quiet`` can skip
+the initial scan of the source directory, this may shorten the backup
+time needed for large directories.
 
 Additionally on Unix systems if ``restic`` receives a SIGUSR1 signal the
 current progress will written to the standard output so you can check up