Editor: Fix restoring current cursor line after autoformat takes place

- The previous solution was giving a segfault when auto-formatting on
save is enabled.
- Add test to check this functionality and auto-formatting on save.

Author: ccordoba12

spyder/plugins/editor/widgets/codeeditor.py

@@ -526,7 +526,7 @@ def __init__(self, parent=None):
         self.format_on_save = False
         self.format_eventloop = QEventLoop(None)
         self.format_timer = QTimer(self)
-        self.__cursor_position_before_format = 0
+        self.__line_number_before_format = 0
 
         # Mouse tracking
         self.setMouseTracking(True)
@@ -1804,10 +1804,6 @@ def handle_go_to_definition(self, position):
     # -------------------------------------------------------------------------
     def format_document_or_range(self):
         """Format current document or selected text."""
-        # Save current cursor position to restore it after the current text has
-        # been replaced by the auto-formatted one.
-        self.__cursor_position_before_format = self.textCursor().position()
-
         if self.has_selected_text() and self.range_formatting_enabled:
             self.format_document_range()
         else:
@@ -1816,6 +1812,8 @@ def format_document_or_range(self):
     @schedule_request(method=CompletionRequestTypes.DOCUMENT_FORMATTING)
     def format_document(self):
         """Format current document."""
+        self.__line_number_before_format = self.textCursor().blockNumber()
+
         if not self.formatting_enabled:
             return
         if self.formatting_in_progress:
@@ -1849,6 +1847,8 @@ def format_document(self):
     @schedule_request(method=CompletionRequestTypes.DOCUMENT_RANGE_FORMATTING)
     def format_document_range(self):
         """Format selected text."""
+        self.__line_number_before_format = self.textCursor().blockNumber()
+
         if not self.range_formatting_enabled or not self.has_selected_text():
             return
         if self.formatting_in_progress:
@@ -2007,18 +2007,22 @@ def _apply_document_edits(self, edits):
             # Insert formatted text in place of the previous one
             cursor.insertText(merged_text)
 
-            # Don't run the lines below when testing because they give
-            # segfaults.
-            if not running_under_pytest():
-                # Restore previous cursor position and center it.
-                # Fixes spyder-ide/spyder#19958
-                cursor.setPosition(self.__cursor_position_before_format)
-                self.setTextCursor(cursor)
-                self.centerCursor()
-
             # End text insertion
             cursor.endEditBlock()
 
+            # Restore previous cursor line and center it.
+            # Fixes spyder-ide/spyder#19958
+            if self.__line_number_before_format < self.blockCount():
+                self.moveCursor(QTextCursor.Start)
+                cursor = self.textCursor()
+                cursor.movePosition(
+                    QTextCursor.Down,
+                    QTextCursor.MoveAnchor,
+                    self.__line_number_before_format
+                )
+                self.setTextCursor(cursor)
+                self.centerCursor()
+
     # ---- LSP: Code folding
     # -------------------------------------------------------------------------
     def compute_whitespace(self, line):

spyder/plugins/editor/widgets/tests/test_formatting.py

@@ -9,9 +9,11 @@
 # Standard library imports
 import os
 import os.path as osp
+import random
 
 # Third party imports
 import pytest
+from qtpy.QtCore import Qt
 from qtpy.QtGui import QTextCursor
 from qtpy.QtWidgets import QMessageBox
 import yapf
@@ -257,3 +259,60 @@ def test_closing_document_formatting(
     code_editor = editorstack.load(str(file_path)).editor
 
     assert code_editor.get_text_with_eol() == expected
+
+
+@pytest.mark.order(1)
+@pytest.mark.parametrize('formatter', [autopep8, black])
+def test_formatting_on_save(completions_editor, formatter, qtbot):
+    """
+    Check that auto-formatting on save works as expected and that we restore
+    the current line after doing it.
+
+    This includes a regression test for issue spyder-ide/spyder#19958
+    """
+    file_path, editorstack, code_editor, completion_plugin = completions_editor
+    text, expected = get_formatter_values(formatter, newline='\n')
+
+    # Set formatter
+    editorstack.set_format_on_save(True)
+    CONF.set(
+        'completions',
+        ('provider_configuration', 'lsp', 'values', 'formatting'),
+        formatter
+    )
+
+    with qtbot.waitSignal(completion_plugin.sig_editor_rpc):
+        completion_plugin.after_configuration_update([])
+    qtbot.wait(2000)
+
+    # Set text in editor
+    code_editor.set_text(text)
+
+    # Notify changes
+    with qtbot.waitSignal(
+            code_editor.completions_response_signal, timeout=30000):
+        code_editor.document_did_change()
+
+    # Set a random current line
+    current_line = random.randint(0, code_editor.blockCount())
+    code_editor.moveCursor(QTextCursor.Start)
+    cursor = code_editor.textCursor()
+    cursor.movePosition(QTextCursor.Down, QTextCursor.MoveAnchor, current_line)
+    code_editor.setTextCursor(cursor)
+    qtbot.wait(500)
+
+    # Make a simple change to the file
+    code_editor.moveCursor(QTextCursor.EndOfLine)
+    qtbot.keyPress(code_editor, Qt.Key_Space)
+    qtbot.wait(500)
+
+    # Save the file
+    with qtbot.waitSignal(
+            code_editor.completions_response_signal, timeout=30000):
+        editorstack.save(force=True)
+    qtbot.wait(500)
+
+    # Check that auto-formatting was applied on save and that we restored the
+    # previous line.
+    assert code_editor.get_text_with_eol() == expected
+    assert code_editor.textCursor().blockNumber() == current_line