ReaderSearch: delay adding to location stack until we change page

Search may highlight matches on the current page, and if there
are no others in the book, we would stay there and resume reading;
but we would get a spurious previous location (ie. in Book map)
that we would not expect keeping, and we may accidently go back
to previous location, losing our reading position.
Avoid this by only adding current page to location stack when
actually leaving the current page.
Because of complications with other reading modes, this is
currently only enabled for CRE document when in page mode.

frontend/apps/reader/modules/readerlink.lua

@@ -712,6 +712,10 @@ function ReaderLink:addCurrentLocationToStack(loc)
     table.insert(self.location_stack, location)
 end
 
+function ReaderLink:popFromLocationStack()
+    return table.remove(self.location_stack)
+end
+
 function ReaderLink:onClearLocationStack(show_notification)
     self.location_stack = {}
     self:onClearForwardLocationStack()

frontend/apps/reader/modules/readersearch.lua

@@ -289,6 +289,9 @@ function ReaderSearch:onShowSearchDialog(text, direction, regex, case_insensitiv
             local res = search_func(self, search_term, param, regex, case_insensitive)
             if res then
                 if self.ui.paging then
+                    if not current_page then -- initial search
+                        current_page = self.ui.paging.current_page
+                    end
                     no_results = false
                     self.ui.link:onGotoLink({page = res.page - 1}, neglect_current_location)
                     self.view.highlight.temp[res.page] = res
@@ -357,8 +360,24 @@ function ReaderSearch:onShowSearchDialog(text, direction, regex, case_insensitiv
                         self.ui.link:onGotoLink({xpointer=valid_link}, neglect_current_location)
                     end
                 end
-                -- Don't add result pages to location ("Go back") stack
-                neglect_current_location = true
+                if not neglect_current_location then
+                    -- Initial search: onGotoLink() has added the current page to the location stack,
+                    -- and we don't want this to be done when showing further pages with results.
+                    -- But if this initial search is showing results on the current page, we don't want
+                    -- the original page added: we will do it when we jump to a different page.
+                    -- For now, only do this with CreDocument. With PDF, whether in single page mode or
+                    -- in scroll mode, the view can scroll a bit when showing results, and we want to
+                    -- allow "go back" to restore the original viewport.
+                    if self.ui.rolling and self.view.view_mode == "page" then
+                        if current_page == (self.ui.rolling and self.ui.document:getCurrentPage() or self.ui.paging.current_page) then
+                            self.ui.link:popFromLocationStack()
+                            neglect_current_location = false
+                        else
+                            -- We won't add further result pages to the location stack ("Go back").
+                            neglect_current_location = true
+                        end
+                    end
+                end
             end
             if no_results then
                 local notification_text