start supporting LÖVE v12

To do this I need some support for multiple versions. And I need an
'error' mode to go with existing 'run' and 'source' modes
(`Current_app`). Most errors will automatically transition to 'source'
editor mode, but some errors aren't really actionable in the editor. For
those we'll use 'error' mode.

The app doesn't yet work with LÖVE v12. There are some unit tests failing
because of differences in font rendering.

app.lua

@@ -8,6 +8,7 @@
 --     and a source editor, while giving each the illusion of complete
 --     control.
 function love.run()
+  App.version_check()
   App.snapshot_love()
   -- Tests always run at the start.
   App.run_tests_and_initialize()

conf.lua

@@ -1,3 +0,0 @@
-function love.conf(t)
-  t.version = '11.4'
-end

main.lua

@@ -71,6 +71,23 @@ function App.load()
   end
 end
 
+function App.version_check()
+  -- available modes: run, error
+  Error_message = nil
+  Error_count = 0
+  -- we'll reuse error mode on load for an initial version check
+  local supported_versions = {'11.4', '12.0'}  -- put the recommended version first
+  local minor_version
+  Major_version, minor_version = love.getVersion()
+  Version = Major_version..'.'..minor_version
+  if array.find(supported_versions, Version) == nil then
+    Current_app = 'error'
+    Error_message = ("This app doesn't support version %s; please use version %s. Press any key to try it with this version anyway."):format(Version, supported_versions[1])
+    print(Error_message)
+    -- continue initializing everything; hopefully we won't have errors during initialization
+  end
+end
+
 function App.initialize_globals()
   if Current_app == 'run' then
     run.initialize_globals()
@@ -136,7 +153,12 @@ function App.focus(in_focus)
 end
 
 function App.draw()
-  if Current_app == 'run' then
+  if Current_app == 'error' then
+    love.graphics.setColor(0,0,1)
+    love.graphics.rectangle('fill', 0,0, App.screen.width, App.screen.height)
+    love.graphics.setColor(1,1,1)
+    love.graphics.printf(Error_message, 40,40, 600)
+  elseif Current_app == 'run' then
     run.draw()
   elseif Current_app == 'source' then
     source.draw()
@@ -167,6 +189,12 @@ function App.keychord_press(chord, key)
     return
   end
   --
+  if Current_app == 'error' then
+    if chord == 'C-c' then
+      love.system.setClipboardText(Error_message)
+    end
+    return
+  end
   if chord == 'C-e' then
     -- carefully save settings
     if Current_app == 'run' then
@@ -202,6 +230,7 @@ function App.keychord_press(chord, key)
 end
 
 function App.textinput(t)
+  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
@@ -217,6 +246,7 @@ 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
@@ -232,6 +262,7 @@ function App.keyreleased(key, scancode)
 end
 
 function App.mousepressed(x,y, mouse_button)
+  if Current_app == 'error' then return end
 --?   print('mouse press', x,y)
   if Current_app == 'run' then
     if run.mouse_press then run.mouse_press(x,y, mouse_button) end
@@ -243,6 +274,7 @@ function App.mousepressed(x,y, mouse_button)
 end
 
 function App.mousereleased(x,y, mouse_button)
+  if Current_app == 'error' then return end
   if Current_app == 'run' then
     if run.mouse_release then run.mouse_release(x,y, mouse_button) end
   elseif Current_app == 'source' then
@@ -253,6 +285,7 @@ function App.mousereleased(x,y, mouse_button)
 end
 
 function App.wheelmoved(dx,dy)
+  if Current_app == 'error' then return end
   if Current_app == 'run' then
     if run.mouse_wheel_move then run.mouse_wheel_move(dx,dy) end
   elseif Current_app == 'source' then
@@ -263,6 +296,7 @@ function App.wheelmoved(dx,dy)
 end
 
 function love.quit()
+  if Current_app == 'error' then return end
   if Current_app == 'run' then
     local source_settings = Settings.source
     Settings = run.settings()