Edit book: If the book being edited is deleted instead of showing an error message on save, ask the user to choose a new file location before saving.

src/calibre/ebooks/oeb/polish/container.py

@@ -985,9 +985,13 @@ class EpubContainer(Container):
             f.write(guess_type('a.epub'))
         zip_rebuilder(self.root, outpath)
 
-    @property
+    @dynamic_property
     def path_to_ebook(self):
-        return self.pathtoepub
+        def fget(self):
+            return self.pathtoepub
+        def fset(self, val):
+            self.pathtoepub = val
+        return property(fget=fget, fset=fset)
 
 # }}}
 
@@ -1097,9 +1101,13 @@ class AZW3Container(Container):
             outpath = self.pathtoazw3
         opf_to_azw3(self.name_path_map[self.opf_name], outpath, self.log)
 
-    @property
+    @dynamic_property
     def path_to_ebook(self):
-        return self.pathtoazw3
+        def fget(self):
+            return self.pathtoazw3
+        def fset(self, val):
+            self.pathtoazw3 = val
+        return property(fget=fget, fset=fset)
 
     @property
     def names_that_must_not_be_changed(self):

src/calibre/gui2/__init__.py

@@ -722,7 +722,7 @@ def choose_files(window, name, title,
         return fd.get_files()
     return None
 
-def choose_save_file(window, name, title, filters=[], all_files=True):
+def choose_save_file(window, name, title, filters=[], all_files=True, initial_dir=None):
     '''
     Ask user to choose a file to save to. Can be a non-existent file.
     :param filters: list of allowable extensions. Each element of the list
@@ -731,9 +731,12 @@ def choose_save_file(window, name, title, filters=[], all_files=True):
                      of extensions.
     :param all_files: If True add All files to filters.
     '''
-    mode = QFileDialog.AnyFile
+    kwargs = dict(title=title, name=name, filters=filters,
-    fd = FileDialog(title=title, name=name, filters=filters,
+                    parent=window, add_all_files_filter=all_files, mode=QFileDialog.AnyFile)
-                    parent=window, add_all_files_filter=all_files, mode=mode)
+    if initial_dir is not None:
+        kwargs['no_save_dir'] = True
+        kwargs['default_dir'] = initial_dir
+    fd = FileDialog(**kwargs)
     fd.setParent(None)
     ans = None
     if fd.accepted:

src/calibre/gui2/tweak_book/boss.py

@@ -31,7 +31,7 @@ from calibre.gui2.dialogs.message_box import MessageBox
 from calibre.gui2.tweak_book import set_current_container, current_container, tprefs, actions, editors
 from calibre.gui2.tweak_book.undo import GlobalUndoHistory
 from calibre.gui2.tweak_book.file_list import NewFileDialog
-from calibre.gui2.tweak_book.save import SaveManager, save_container
+from calibre.gui2.tweak_book.save import SaveManager, save_container, find_first_existing_ancestor
 from calibre.gui2.tweak_book.preview import parse_worker, font_cache
 from calibre.gui2.tweak_book.toc import TOCEditor
 from calibre.gui2.tweak_book.editor import editor_from_syntax, syntax_from_mime
@@ -829,6 +829,22 @@ class Boss(QObject):
             if ed.is_modified or not ed.is_synced_to_container:
                 self.commit_editor_to_container(name, c)
                 ed.is_modified = False
+        destdir = os.path.dirname(c.path_to_ebook)
+        if not os.path.exists(destdir):
+            info_dialog(self.gui, _('Path does not exist'), _(
+                'The file you are editing (%s) no longer exists. You have to choose a new save location.') % c.path_to_ebook,
+                        show_copy_button=False, show=True)
+            fmt = c.path_to_ebook.rpartition('.')[-1].lower()
+            start_dir = find_first_existing_ancestor(c.path_to_ebook)
+            path = choose_save_file(self.gui, 'choose-new-save-location', _('Choose file location'), initial_dir=start_dir,
+                                    filters=[(fmt.upper(), (fmt,))], all_files=False)
+            if path is not None:
+                if not path.lower().endswith('.' + fmt):
+                    path = path + '.' + fmt
+                c.path_to_ebook = path
+                self.global_undo.update_path_to_ebook(path)
+            else:
+                return
         self.gui.action_save.setEnabled(False)
         tdir = self.mkdtemp(prefix='save-')
         container = clone_container(c, tdir)
@@ -868,7 +884,8 @@ class Boss(QObject):
             return
         error_dialog(self.gui, _('Could not save'),
                      _('Saving of the book failed. Click "Show Details"'
-                       ' for more information.'), det_msg=tb, show=True)
+                       ' for more information. You can try to save a copy'
+                       ' to a different location, via File->Save a Copy'), det_msg=tb, show=True)
 
     def go_to_line_number(self):
         ed = self.gui.central.current_editor

src/calibre/gui2/tweak_book/save.py

@@ -40,6 +40,14 @@ def send_message(msg=''):
             t.conn.send('bookedited:'+msg)
             t.conn.close()
 
+def find_first_existing_ancestor(path):
+    while path and not os.path.exists(path):
+        npath = os.path.dirname(path)
+        if npath == path:
+            break
+        path = npath
+    return path
+
 class SaveWidget(QWidget):
 
     def __init__(self, parent=None):

src/calibre/gui2/tweak_book/undo.py

@@ -167,6 +167,10 @@ class GlobalUndoHistory(QAbstractListModel):
             return ''
         return self.states[self.pos + 1].message or _('[Unnamed state]')
 
+    def update_path_to_ebook(self, path):
+        for state in self.states:
+            state.container.path_to_ebook = path
+
 class SpacedDelegate(QStyledItemDelegate):
 
     def sizeHint(self, *args):