internal/pkg: check for unclean shutdown

This avoids running into nasty surprises opening a cache that suffered unclean shutdown due to power loss. All other parts of the cache are not prone to inconsistent state.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/pkg_test.go

@@ -1852,6 +1852,49 @@ func TestOpen(t *testing.T) {
 			t.Errorf("Open: error = %#v, want %#v", err, wantErr)
 		}
 	})
+
+	t.Run("dirty", func(t *testing.T) {
+		t.Parallel()
+
+		tempDir := check.MustAbs(t.TempDir())
+		if err := os.MkdirAll(tempDir.Append(
+			"cache",
+			"work",
+			"dirty",
+		).String(), 0755); err != nil {
+			t.Fatal(err)
+		}
+
+		wantErr := errors.New("work is not empty, scrub likely required")
+		if _, err := pkg.Open(
+			t.Context(),
+			message.New(nil),
+			0, 0, 0, tempDir.Append("cache"),
+		); !reflect.DeepEqual(err, wantErr) {
+			t.Errorf("Open: error = %#v, want %#v", err, wantErr)
+		}
+	})
+
+	t.Run("scratch", func(t *testing.T) {
+		t.Parallel()
+
+		tempDir := check.MustAbs(t.TempDir())
+		if err := os.MkdirAll(tempDir.Append(
+			"cache",
+			"scratch",
+		).String(), 0755); err != nil {
+			t.Fatal(err)
+		}
+
+		wantErr := errors.New("scratch is present, scrub likely required")
+		if _, err := pkg.Open(
+			t.Context(),
+			message.New(nil),
+			0, 0, 0, tempDir.Append("cache"),
+		); !reflect.DeepEqual(err, wantErr) {
+			t.Errorf("Open: error = %#v, want %#v", err, wantErr)
+		}
+	})
 }
 
 func TestExtensionRegister(t *testing.T) {