feat: implement traverse support for :CommandT

Rather hacky, so want to test this a bit to make sure it works, probably
refactor it to make it less hacky, and then roll out coverage to the
other file-oriented finder types.

In the end, treating explicit path arguments as overriding the inferred
root directory; ie. `:CommandT foo` or `:CommandT ..` won't do
traversal, but `:CommandT` will.

In all cases, this behaves as if you `cd`'d into the root (either
explicitly specified or found via traversal) ran the command, and the
`cd`'d back. The match listing shows candidates relative to that root.

Author: wincent

lua/wincent/commandt/init.lua

@@ -615,13 +615,34 @@ end
 
 commandt.file_finder = function(directory)
   directory = vim.trim(directory)
+  local previous_cwd = vim.uv.cwd()
+  local next_cwd = previous_cwd
   if directory == '' then
-    directory = '.'
+    next_cwd = get_directory()
   end
   local ui = require('wincent.commandt.private.ui')
   local options = commandt.options()
-  local finder = require('wincent.commandt.private.finders.file')(directory, options)
-  ui.show(finder, merge(options, { name = 'file' }))
+  if previous_cwd ~= next_cwd then
+    vim.fn.chdir(get_directory())
+  end
+
+  local finder = require('wincent.commandt.private.finders.file')('.', options)
+  ui.show(finder, merge(options, {
+    name = 'file',
+    on_open = function(result)
+      if previous_cwd ~= next_cwd then
+        result = vim.fs.normalize(
+          vim.fs.joinpath(next_cwd, result)
+        )
+      end
+      return result
+    end,
+    on_close = function()
+      if previous_cwd ~= next_cwd then
+        vim.fn.chdir(previous_cwd)
+      end
+    end,
+  }))
 end
 
 local report_errors = function(errors, heading)

lua/wincent/commandt/private/ui.lua

@@ -12,6 +12,8 @@ local cmdline_enter_autocmd = nil
 local current_finder = nil -- Reference to avoid premature garbage collection.
 local current_window = nil
 local match_listing = nil
+local on_close = nil
+local on_open = nil
 local prompt = nil
 local results = nil
 local selected = nil
@@ -61,17 +63,26 @@ local close = function()
     current_window = nil
     vim.api.nvim_set_current_win(win)
   end
+  if on_close then
+    on_close()
+    on_close = nil
+  end
 end
 
 ui.open = function(kind)
   close()
   if results and #results > 0 then
-    -- Defer, to give autocommands a chance to run.
     local result = results[selected]
+    if on_open then
+      result = on_open(result)
+    end
+
+    -- Defer, to give autocommands a chance to run.
     vim.defer_fn(function()
       current_finder.open(result, kind)
     end, 0)
   end
+  on_open = nil
 end
 
 ui.show = function(finder, options)
@@ -80,6 +91,9 @@ ui.show = function(finder, options)
 
   current_window = vim.api.nvim_get_current_win()
 
+  on_close = options.on_close
+  on_open = options.on_open
+
   -- Temporarily override global settings.
   -- For now just 'hlsearch', but may add more later (see
   -- ruby/command-t/lib/command-t/match_window.rb)