redo version checks yet again

I'm starting to feel better after replacing 1 line with 20 and 2 new
bits of global state. I'm now handling two scenarios more explicitly:

* If I change Current_app within key_press, the corresponding text_input
  and key_release events go to the new app. If it's an editor it might
  insert the key, which is undesirable. Putting such handlers in
  key_release now feels overly clever, particularly since it took me
  forever to realize why I was getting stuck in an infinite loop.

* Both 'run' and 'source' can hit the version check, so we need to be
  able to transition from the 'error' app to either. Which
  necessitates yet another global bit of state: Next_app.

Manual_tests.md

@@ -30,7 +30,7 @@ Code loading:
     - analogously, how a shape precisely looks as you draw it
 
 * start out running the text editor, press ctrl+e to edit source, make a change to the source, press ctrl+e twice to return to the source editor; the change should be preserved.
-* run with an untested version. Error message pops up. Press a key. Text editor comes up, and doesn't receive the key. Press ctrl+e. Source editor opens up. Press ctrl+e. Text editor returns.
+* run with an untested version. Error message pops up. Press a key. Text editor comes up, and doesn't receive the key. Press ctrl+e. Error pops up. Press a key. Source editor opens up. Press ctrl+e. Error pops up. Press a key. Text editor returns.
 * create a couple of spuriously failing tests. Run with an untested version. Error message includes message about untested version.
 
 ### Other compromises

app.lua

@@ -12,7 +12,6 @@ function love.run()
   App.snapshot_love()
   -- Tests always run at the start.
   App.run_tests_and_initialize()
-  App.love_version_check()  -- hack: we want to run this just the first time and not every time we bounce between 'run' and 'source'
 --?   print('==')
 
   love.timer.step()

main.lua

@@ -89,25 +89,30 @@ function App.initialize_globals()
   Current_time = 0
   Last_focus_time = 0  -- https://love2d.org/forums/viewtopic.php?p=249700
   Last_resize_time = 0
+
+  -- Another weird bit for a class of corner cases. E.g.:
+  -- * I press ctrl+e, switch Current_app. I don't want the new app to receive
+  --   text_input and key_release events.
+  -- If I try to avoid text_input events by switching modes on key_release, I
+  -- hit a new problem:
+  -- * I press ctrl+e, am running an untested version, Current_app goes to
+  --   'error', and immediately rolls back out of 'error' in the key_release
+  --   event.
+  -- Skip_rest_of_key_events is ugly, but feels cleaner than creating yet
+  -- another possible value for Current_app.
+  Skip_rest_of_key_events = nil
+
+  -- Where to go from 'error' app.
+  Next_app = nil
 end
 
 function check_love_version_for_tests()
   if array.find(Supported_versions, Version) == nil then
-    Unsupported_version = true
     -- warning to include in an error message if any tests failed
     Warning_before_tests = ("This app hasn't been tested with LÖVE version %s."):format(Version)
   end
 end
 
-function App.love_version_check()
-  if Unsupported_version then
-    Current_app = 'error'
-    Error_message = ("This app hasn't been tested with LÖVE version %s; please switch to version %s if you run into issues. Press any key to continue."):format(Version, Supported_versions[1])
-    print(Error_message)
-    -- continue initializing everything; hopefully we won't have errors during initialization
-  end
-end
-
 function App.initialize(arg)
   love.keyboard.setTextInput(true)  -- bring up keyboard on touch screen
   love.keyboard.setKeyRepeat(true)
@@ -122,14 +127,25 @@ function App.initialize(arg)
   else
     assert(false, 'unknown app "'..Current_app..'"')
   end
+
+  check_love_version()
+end
+
+function check_love_version()
+  if array.find(Supported_versions, Version) == nil then
+    Next_app = Current_app
+    Current_app = 'error'
+    Error_message = ("This app hasn't been tested with LÖVE version %s; please switch to version %s if you run into issues. Press any key to continue."):format(Version, Supported_versions[1])
+    -- continue initializing everything; hopefully we won't have errors during initialization
+  end
 end
 
 function App.resize(w,h)
+  if Current_app == 'error' then return end
   if Current_app == 'run' then
     if run.resize then run.resize(w,h) end
   elseif Current_app == 'source' then
     if source.resize then source.resize(w,h) end
-  elseif Current_app == 'error' then
   else
     assert(false, 'unknown app "'..Current_app..'"')
   end
@@ -137,17 +153,18 @@ function App.resize(w,h)
 end
 
 function App.filedropped(file)
+  if Current_app == 'error' then return end
   if Current_app == 'run' then
     if run.file_drop then run.file_drop(file) end
   elseif Current_app == 'source' then
     if source.file_drop then source.file_drop(file) end
-  elseif Current_app == 'error' then
   else
     assert(false, 'unknown app "'..Current_app..'"')
   end
 end
 
 function App.focus(in_focus)
+  if Current_app == 'error' then return end
   if in_focus then
     Last_focus_time = Current_time
   end
@@ -155,7 +172,6 @@ function App.focus(in_focus)
     if run.focus then run.focus(in_focus) end
   elseif Current_app == 'source' then
     if source.focus then source.focus(in_focus) end
-  elseif Current_app == 'error' then
   else
     assert(false, 'unknown app "'..Current_app..'"')
   end
@@ -178,6 +194,7 @@ end
 
 function App.update(dt)
   Current_time = Current_time + dt
+  if Current_app == 'error' then return end
   -- some hysteresis while resizing
   if Current_time < Last_resize_time + 0.1 then
     return
@@ -187,7 +204,6 @@ function App.update(dt)
     run.update(dt)
   elseif Current_app == 'source' then
     source.update(dt)
-  elseif Current_app == 'error' then
   else
     assert(false, 'unknown app "'..Current_app..'"')
   end
@@ -199,9 +215,14 @@ function App.keychord_press(chord, key)
     return
   end
   --
+  Skip_rest_of_key_events = nil
   if Current_app == 'error' then
     if chord == 'C-c' then
       love.system.setClipboardText(Error_message)
+    else
+      Current_app = Next_app
+      Next_app = nil
+      Skip_rest_of_key_events = true
     end
     return
   end
@@ -229,6 +250,7 @@ function App.keychord_press(chord, key)
     load_file_from_source_or_save_directory('main.lua')
     App.undo_initialize()
     App.run_tests_and_initialize()
+    Skip_rest_of_key_events = true
     return
   end
   if Current_app == 'run' then
@@ -247,6 +269,7 @@ function App.textinput(t)
     return
   end
   --
+  if Skip_rest_of_key_events then return end
   if Current_app == 'run' then
     if run.text_input then run.text_input(t) end
   elseif Current_app == 'source' then
@@ -257,14 +280,14 @@ function App.textinput(t)
 end
 
 function App.keyreleased(key, scancode)
+  if Current_app == 'error' then return end
   -- ignore events for some time after window in focus (mostly alt-tab)
   if Current_time < Last_focus_time + 0.01 then
     return
   end
   --
-  if Current_app == 'error' then
+  if Skip_rest_of_key_events then return end
-    Current_app = 'run'
+  if Current_app == 'run' then
-  elseif Current_app == 'run' then
     if run.key_release then run.key_release(key, scancode) end
   elseif Current_app == 'source' then
     if source.key_release then source.key_release(key, scancode) end