start showing source menu file navigation state graphically

I'm a bit leery of going down this road:

- If there's a bug in how I render logs graphically that could be
  extremely misleading. Perhaps this suggests that the code to log
  things should be significantly simpler than the code that might be
  debugged. If writing the debug helper requires all my smarts I'm not
  smart enough to debug using the helper, etc. Given this idea, the fact
  that I'm copying production code into the logging helper is
  concerning.

- There's a question of what code it's ok for logging helpers to depend
  on. This is an issue shared with tests. I often implicitly (and
  without meaning to) assume the presence of some well-tested helpers
  when writing tests. If those helpers ever break I can get into a
  rabbit hole of debugging. This problem might be even more insidious
  with logging helpers that will give me no indication when they break.

Still and all, it's cool to see menus in my logs. Let's see if it's
useful.

commands.lua

@@ -54,10 +54,10 @@ end
 
 function source.draw_file_navigator()
   if File_navigation.num_lines == nil then
-    File_navigation.num_lines = source.num_lines_for_file_navigator()
+    File_navigation.num_lines = source.num_lines_for_file_navigator(File_navigation.candidates)
   end
   App.color(Menu_background_color)
-  love.graphics.rectangle('fill', 0,Menu_status_bar_height, App.screen.width, File_navigation.num_lines * Editor_state.line_height)
+  love.graphics.rectangle('fill', 0,Menu_status_bar_height, App.screen.width, File_navigation.num_lines * Editor_state.line_height + --[[highlight padding]] 2)
   local x,y = 5, Menu_status_bar_height
   for i,filename in ipairs(File_navigation.candidates) do
     if filename == 'source' then
@@ -71,10 +71,10 @@ function source.draw_file_navigator()
   end
 end
 
-function source.num_lines_for_file_navigator()
+function source.num_lines_for_file_navigator(candidates)
   local result = 1
   local x = 5
-  for i,filename in ipairs(File_navigation.candidates) do
+  for i,filename in ipairs(candidates) do
     local width = App.width(to_text(filename))
     if x + width > App.screen.width - 5 then
       result = result+1
@@ -105,7 +105,7 @@ end
 
 function keychord_pressed_on_file_navigator(chord, key)
   log(2, 'file navigator: '..chord)
-  log(2, ('cursor initially at %d %s'):format(File_navigation.index, File_navigation.candidates[File_navigation.index]))
+  log(2, {name='file_navigator_state', files=File_navigation.candidates, index=File_navigation.index})
   if chord == 'escape' then
     Show_file_navigator = false
   elseif chord == 'return' then
@@ -127,6 +127,54 @@ function keychord_pressed_on_file_navigator(chord, key)
   end
 end
 
+function log_render.file_navigator_state(o, x,y, w)
+  -- duplicate structure of source.draw_file_navigator
+  local num_lines = source.num_lines_for_file_navigator(o.files)
+  local h = num_lines * Editor_state.line_height
+  App.color(Menu_background_color)
+  love.graphics.rectangle('fill', x,y, w,h)
+  -- compute the x,y,width of the current index (in offsets from top left)
+  local x2,y2 = 0,0
+  local width = 0
+  for i,filename in ipairs(o.files) do
+    local filename_text = to_text(filename)
+    width = App.width(filename_text)
+    if x2 + width > App.screen.width - 5 then
+      y2 = y2 + Editor_state.line_height
+      x2 = 0
+    end
+    if i == o.index then
+      break
+    end
+    x2 = x2 + width + 30
+  end
+  -- figure out how much of the menu to display
+  local menu_xmin = math.max(0, x2-w/2)
+  local menu_xmax = math.min(App.screen.width, x2+w/2)
+  -- now selectively print out entries
+  local x3,y3 = 0,y  -- x3 is relative, y3 is absolute
+  local width = 0
+  for i,filename in ipairs(o.files) do
+    local filename_text = to_text(filename)
+    width = App.width(filename_text)
+    if x3 + width > App.screen.width - 5 then
+      y3 = y3 + Editor_state.line_height
+      x3 = 0
+    end
+    if i == o.index then
+      App.color(Menu_highlight_color)
+      love.graphics.rectangle('fill', x + x3-menu_xmin - 5, y3-2, width+5*2, Editor_state.line_height+2*2)
+    end
+    if x3 >= menu_xmin and x3 + width < menu_xmax then
+      App.color(Menu_command_color)
+      App.screen.draw(filename_text, x + x3-menu_xmin, y3)
+    end
+    x3 = x3 + width + 30
+  end
+  --
+  return h+20
+end
+
 function file_navigator_up()
   local y, x, width = file_coord(File_navigation.index)
   local index = file_index(y-Editor_state.line_height, x, width)

source.lua

@@ -1,4 +1,5 @@
 source = {}
+log_render = {}
 
 Editor_state = {}