Exit non-zero when snapshot create --skip-errors skips anything it cannot read (closes #310)

A backup under --skip-errors printed its skip errors, then "Finished
successfully.", and exited 0, so a cron wrapper could not tell it from
a complete backup.

Each skipped entry, including a directory the walk could not list, is
now counted as examined and failed. If --skip-errors skipped anything
it could not read or list, the run still keeps its snapshots and
prunes as before, then fails with "Backup completed, but N file(s)
could not be read". A file removed during the run, even before the
walk reaches it, counts once as failed and leaves the exit status
alone; without the flag it no longer stops the backup. Excluded
entries are never counted.

Model: opus-5-5

internal/vaultik/snapshot_skip_errors_test.go

@@ -3,6 +3,7 @@ package vaultik_test
 import (
 	"context"
 	"fmt"
+	"os"
 	"path/filepath"
 	"testing"
 
@@ -73,3 +74,144 @@ func TestSkipErrorsBackupStopsOnIndexErrorRecordingDirectory(t *testing.T) {
 	require.Len(t, snapshots, 1)
 	assert.Nil(t, snapshots[0].CompletedAt)
 }
+
+// A backup under --skip-errors that skips a file it cannot open, or a
+// directory it cannot list, keeps the snapshot, counts what it skipped
+// as failed and returns an error instead of finishing successfully. See
+// https://git.eeqj.de/sneak/vaultik/issues/310.
+func TestSkipErrorsBackupKeepsSnapshotAndFailsWhenItSkips(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	tests := []struct {
+		name    string
+		skipped string // relative to the source directory
+	}{
+		{name: "file it cannot open", skipped: "skipdir/file.txt"},
+		{name: "directory it cannot list", skipped: "skipdir"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			env := newDeletedCountEnv(t, map[string][]byte{
+				"stored.txt":       []byte("stored"),
+				"skipdir/file.txt": []byte("in skipdir"),
+			})
+			env.setSnapshot("work", "")
+
+			// A mode does not lock out root, who runs the tests, so
+			// opening the skipped path is made to fail instead.
+			env.v.Fs = &openFailFs{
+				path: filepath.Join(env.src, tt.skipped),
+				err:  os.ErrPermission,
+			}
+
+			err := env.v.CreateSnapshot(&vaultik.SnapshotCreateOptions{
+				SkipErrors: true,
+				Snapshots:  []string{"work"},
+			})
+			require.ErrorIs(t, err, vaultik.ErrFilesUnreadable)
+
+			assert.Contains(t, env.out.String(),
+				"Files: 2 examined, 1 backed up, 0 unchanged, 1 failed.")
+			assert.NotContains(t, env.out.String(), "Finished successfully.")
+
+			snapshots, err := env.v.Repositories.Snapshots.ListRecent(
+				context.Background(), listRecentTestLimit)
+			require.NoError(t, err)
+			require.Len(t, snapshots, 1)
+			assert.NotNil(t, snapshots[0].CompletedAt, "the snapshot is kept")
+		})
+	}
+}
+
+// removeOnLookupFs is the real filesystem, except that path is removed
+// just before it is looked up. The walk looks an entry up after listing
+// its directory, so path is listed but gone when the walk reaches it.
+type removeOnLookupFs struct {
+	afero.OsFs
+
+	path string
+}
+
+func (f *removeOnLookupFs) LstatIfPossible(
+	name string,
+) (os.FileInfo, bool, error) {
+	if name == f.path {
+		_ = os.Remove(name)
+	}
+
+	return f.OsFs.LstatIfPossible(name)
+}
+
+// A file removed before the walk reaches it is counted once, as failed,
+// like a file removed before its data is read, and the backup finishes
+// successfully, with or without --skip-errors. See
+// https://git.eeqj.de/sneak/vaultik/issues/310.
+func TestBackupCountsFileRemovedBeforeWalkReachesItAsFailed(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	tests := []struct {
+		name       string
+		skipErrors bool
+	}{
+		{name: "under skip-errors", skipErrors: true},
+		{name: "without skip-errors", skipErrors: false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			env := newDeletedCountEnv(t, map[string][]byte{
+				"stays.txt":   []byte("stays"),
+				"removed.txt": []byte("removed"),
+			})
+			env.setSnapshot("walk", "")
+
+			// The previous snapshot has the file, so a removal the walk
+			// also counted as deleted would show.
+			env.backUp(t, "walk")
+
+			env.v.Fs = &removeOnLookupFs{
+				path: filepath.Join(env.src, "removed.txt"),
+			}
+
+			env.out.Reset()
+			require.NoError(t, env.v.CreateSnapshot(&vaultik.SnapshotCreateOptions{
+				SkipErrors: tt.skipErrors,
+				Snapshots:  []string{"walk"},
+			}))
+			assert.Contains(t, env.out.String(),
+				"Files: 2 examined, 0 backed up, 1 unchanged, 1 failed.")
+			assert.Contains(t, env.out.String(), "Finished successfully.")
+		})
+	}
+}
+
+// A file an exclude pattern matches is not counted when it is removed
+// before the walk reaches it. See
+// https://git.eeqj.de/sneak/vaultik/issues/310.
+func TestBackupIgnoresExcludedFileRemovedBeforeWalkReachesIt(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	env := newDeletedCountEnv(t, map[string][]byte{
+		"stays.txt":   []byte("stays"),
+		"removed.tmp": []byte("removed"),
+	})
+	env.setSnapshot("walk", "", "*.tmp")
+	env.v.Fs = &removeOnLookupFs{
+		path: filepath.Join(env.src, "removed.tmp"),
+	}
+
+	require.NoError(t, env.v.CreateSnapshot(&vaultik.SnapshotCreateOptions{
+		SkipErrors: true,
+		Snapshots:  []string{"walk"},
+	}))
+	assert.Contains(t, env.out.String(), filesLine(1, 1, 0))
+	assert.Contains(t, env.out.String(), "Finished successfully.")
+}