feat(performance): Major performance improvements using async v2 from @oberblastmeister (#987)

* start: Working w/ async jobs

* short circuit to using bad finder if you pass writer.

lua/telescope/sorters.lua

@@ -96,10 +96,10 @@ function Sorter:_start(prompt)
   local len_previous = #previous
 
   if #prompt < len_previous then
-    log.debug "Reset discard because shorter prompt"
+    log.trace "Reset discard because shorter prompt"
     self._discard_state.filtered = {}
   elseif string.sub(prompt, 1, len_previous) ~= previous then
-    log.debug "Reset discard no match"
+    log.trace "Reset discard no match"
     self._discard_state.filtered = {}
   end
 
@@ -167,11 +167,10 @@ end
 
 sorters.Sorter = Sorter
 
-TelescopeCachedTails = TelescopeCachedTails or nil
-if not TelescopeCachedTails then
+local make_cached_tail = function()
   local os_sep = util.get_separator()
   local match_string = "[^" .. os_sep .. "]*$"
-  TelescopeCachedTails = setmetatable({}, {
+  return setmetatable({}, {
     __index = function(t, k)
       local tail = string.match(k, match_string)
 
@@ -181,8 +180,8 @@ if not TelescopeCachedTails then
   })
 end
 
-TelescopeCachedUppers = TelescopeCachedUppers
-  or setmetatable({}, {
+local make_cached_uppers = function()
+  return setmetatable({}, {
     __index = function(t, k)
       local obj = {}
       for i = 1, #k do
@@ -196,8 +195,7 @@ TelescopeCachedUppers = TelescopeCachedUppers
       return obj
     end,
   })
-
-TelescopeCachedNgrams = TelescopeCachedNgrams or {}
+end
 
 -- TODO: Match on upper case words
 -- TODO: Match on last match
@@ -206,9 +204,11 @@ sorters.get_fuzzy_file = function(opts)
 
   local ngram_len = opts.ngram_len or 2
 
+  local cached_ngrams = {}
+
   local function overlapping_ngrams(s, n)
-    if TelescopeCachedNgrams[s] and TelescopeCachedNgrams[s][n] then
-      return TelescopeCachedNgrams[s][n]
+    if cached_ngrams[s] and cached_ngrams[s][n] then
+      return cached_ngrams[s][n]
     end
 
     local R = {}
@@ -216,15 +216,18 @@ sorters.get_fuzzy_file = function(opts)
       R[#R + 1] = s:sub(i, i + n - 1)
     end
 
-    if not TelescopeCachedNgrams[s] then
-      TelescopeCachedNgrams[s] = {}
+    if not cached_ngrams[s] then
+      cached_ngrams[s] = {}
     end
 
-    TelescopeCachedNgrams[s][n] = R
+    cached_ngrams[s][n] = R
 
     return R
   end
 
+  local cached_tails = make_cached_tail()
+  local cached_uppers = make_cached_uppers()
+
   return Sorter:new {
     scoring_function = function(_, prompt, line)
       local N = #prompt
@@ -243,8 +246,8 @@ sorters.get_fuzzy_file = function(opts)
       -- Contains the original string
       local contains_string = line_lower:find(prompt_lower, 1, true)
 
-      local prompt_uppers = TelescopeCachedUppers[prompt]
-      local line_uppers = TelescopeCachedUppers[line]
+      local prompt_uppers = cached_uppers[prompt]
+      local line_uppers = cached_uppers[line]
 
       local uppers_matching = 0
       for k, _ in pairs(prompt_uppers) do
@@ -254,7 +257,7 @@ sorters.get_fuzzy_file = function(opts)
       end
 
       -- TODO: Consider case senstivity
-      local tail = TelescopeCachedTails[line_lower]
+      local tail = cached_tails[line_lower]
       local contains_tail = tail:find(prompt, 1, true)
 
       local consecutive_matches = 0
@@ -313,9 +316,10 @@ sorters.get_generic_fuzzy_sorter = function(opts)
 
   local ngram_len = opts.ngram_len or 2
 
+  local cached_ngrams = {}
   local function overlapping_ngrams(s, n)
-    if TelescopeCachedNgrams[s] and TelescopeCachedNgrams[s][n] then
-      return TelescopeCachedNgrams[s][n]
+    if cached_ngrams[s] and cached_ngrams[s][n] then
+      return cached_ngrams[s][n]
     end
 
     local R = {}
@@ -323,11 +327,11 @@ sorters.get_generic_fuzzy_sorter = function(opts)
       R[#R + 1] = s:sub(i, i + n - 1)
     end
 
-    if not TelescopeCachedNgrams[s] then
-      TelescopeCachedNgrams[s] = {}
+    if not cached_ngrams[s] then
+      cached_ngrams[s] = {}
     end
 
-    TelescopeCachedNgrams[s][n] = R
+    cached_ngrams[s][n] = R
 
     return R
   end
@@ -462,6 +466,9 @@ sorters.get_fzy_sorter = function(opts)
   }
 end
 
+-- TODO: Could probably do something nice where we check their conf
+--          and choose their default for this.
+--          But I think `fzy` is good default for now.
 sorters.highlighter_only = function(opts)
   opts = opts or {}
   local fzy = opts.fzy_mod or require "telescope.algos.fzy"