Make sure the document isn't overwritten if it exists, but we have an error loading it due to encoding, or otherwise

nw/gui/doceditor.py

@@ -162,9 +162,21 @@ class GuiDocEditor(QTextEdit):
         return True
 
     def loadText(self, tHandle):
+        """Load text from a document into the editor. If we have an io error, we must handle this
+        and clear the editor so that we don't risk overwriting the file if it exists. This can for
+        instance happen of the file contains binary elements or an encoding that novelWriter does
+        not support. If load is successful, ot the document is new (empty string) we set up the
+        editor for editing the file.
+        """
+
+        theDoc = self.nwDocument.openDocument(tHandle)
+        if theDoc is None:
+            # There was an io error
+            self.clearEditor()
+            return False
 
         self.hLight.setHandle(tHandle)
-        self.setPlainText(self.nwDocument.openDocument(tHandle))
+        self.setPlainText(theDoc)
         self.setCursorPosition(self.nwDocument.theItem.cursorPos)
         self.lastEdit = time()
         self._runCounter()

nw/gui/winmain.py

@@ -332,10 +332,12 @@ class GuiMain(QMainWindow):
     def openDocument(self, tHandle):
         if self.hasProject:
             self.closeDocument()
-            self.docEditor.loadText(tHandle)
-            self.docEditor.setFocus()
-            self.docEditor.changeWidth()
-            self.theProject.setLastEdited(tHandle)
+            if self.docEditor.loadText(tHandle):
+                self.docEditor.setFocus()
+                self.docEditor.changeWidth()
+                self.theProject.setLastEdited(tHandle)
+            else:
+                return False
         return True
 
     def saveDocument(self):

nw/project/document.py

@@ -57,8 +57,13 @@ class NWDoc():
                     theDoc = inFile.read()
             except Exception as e:
                 self.makeAlert(["Failed to open document file.",str(e)], nwAlert.ERROR)
-                return ""
+                # Note: Document must be cleared in case of an io error, or else the auto-save or
+                # save will try to overwrite it with an empty file. Return None to alert the caller.
+                self.clearDocument()
+                return None
         else:
+            # The document file does not exist, so we assume it's a new document and initialise an
+            # empty text string.
             logger.debug("The requested document does not exist.")
             return ""