Fix BusyCursor to use internal stack provided by setOverrideCursor/restoreOverrideCursor (#1827)

* un-busy as many times as needed

* lint

* add test to prove cursor behavior

* tentative change in the hopes that all supported qt versions behave properly

* remove unnecessary code

* use contextmanager decorator instead of class

* use full path to WaitCursor

* restore docstring; refactor variable for clarity

* fix docstring whitespace

* break up long lines

* use variable to shorten instead

pyqtgraph/widgets/BusyCursor.py

@@ -1,35 +1,28 @@
-from ..Qt import QtGui, QtCore, QT_LIB
+# -*- coding: utf-8 -*-
+from contextlib import contextmanager
 
-__all__ = ['BusyCursor']
+from ..Qt import QtGui, QtCore
 
-class BusyCursor(object):
-    """Class for displaying a busy mouse cursor during long operations.
+__all__ = ["BusyCursor"]
+
+
+@contextmanager
+def BusyCursor():
+    """
+    Display a busy mouse cursor during long operations.
     Usage::
 
-        with pyqtgraph.BusyCursor():
+        with BusyCursor():
             doLongOperation()
 
     May be nested. If called from a non-gui thread, then the cursor will not be affected.
     """
-    active = []
-
-    def __enter__(self):
-        app = QtCore.QCoreApplication.instance()
-        isGuiThread = (app is not None) and (QtCore.QThread.currentThread() == app.thread())
-        if isGuiThread and QtGui.QApplication.instance() is not None:
-            if QT_LIB == 'PySide':
-                # pass CursorShape rather than QCursor for PySide
-                # see https://bugreports.qt.io/browse/PYSIDE-243
-                QtGui.QApplication.setOverrideCursor(QtCore.Qt.CursorShape.WaitCursor)
-            else:
-                QtGui.QApplication.setOverrideCursor(QtGui.QCursor(QtCore.Qt.CursorShape.WaitCursor))
-            BusyCursor.active.append(self)
-            self._active = True
-        else:
-            self._active = False
-
-    def __exit__(self, *args):
-        if self._active:
-            BusyCursor.active.pop(-1)
-            if len(BusyCursor.active) == 0:
-                QtGui.QApplication.restoreOverrideCursor()
+    app = QtCore.QCoreApplication.instance()
+    in_gui_thread = (app is not None) and (QtCore.QThread.currentThread() == app.thread())
+    try:
+        if in_gui_thread:
+            QtGui.QApplication.setOverrideCursor(QtGui.QCursor(QtCore.Qt.CursorShape.WaitCursor))
+        yield
+    finally:
+        if in_gui_thread:
+            QtGui.QApplication.restoreOverrideCursor()

tests/widgets/test_busycursor.py

@@ -0,0 +1,13 @@
+# -*- coding: utf-8 -*-
+import pyqtgraph as pg
+
+pg.mkQApp()
+
+
+def test_nested_busy_cursors_clear_after_all_exit():
+    with pg.BusyCursor():
+        wait_cursor = pg.Qt.QtCore.Qt.CursorShape.WaitCursor
+        with pg.BusyCursor():
+            assert pg.Qt.QtGui.QApplication.overrideCursor().shape() == wait_cursor, "Cursor should be waiting"
+        assert pg.Qt.QtGui.QApplication.overrideCursor().shape() == wait_cursor, "Cursor should be waiting"
+    assert pg.Qt.QtGui.QApplication.overrideCursor() is None, "No override cursor should be set"