feat: Improve filtering ideas for sorters.

lua/telescope/sorters.lua

@@ -20,6 +20,8 @@ local ngram_highlighter = function(ngram_len, prompt, display)
   return highlights
 end
 
+local FILTERED = -1
+
 
 local Sorter = {}
 Sorter.__index = Sorter
@@ -39,12 +41,68 @@ function Sorter:new(opts)
     state = {},
     scoring_function = opts.scoring_function,
     highlighter = opts.highlighter,
+    discard = opts.discard,
+    _discard_state = {
+      filtered = {},
+      prompt = '',
+    },
   }, Sorter)
 end
 
+-- TODO: We could make this a bit smarter and cache results "as we go" and where they got filtered.
+--          Then when we hit backspace, we don't have to re-caculate everything.
+--          Prime did a lot of the hard work already, but I don't want to copy as much memory around
+--              as he did in his example.
+--              Example can be found in ./scratch/prime_prompt_cache.lua
+function Sorter:_start(prompt)
+  if not self.discard then
+    return
+  end
+
+  local previous = self._discard_state.prompt
+  local len_previous = #previous
+
+  if #prompt < len_previous then
+    log.debug("Reset discard because shorter prompt")
+    self._discard_state.filtered = {}
+  elseif string.sub(prompt, 1, len_previous) ~= previous then
+    log.debug("Reset discard no match")
+    self._discard_state.filtered = {}
+  end
+
+  self._discard_state.prompt = prompt
+end
+
+-- TODO: Consider doing something that makes it so we can skip the filter checks
+--          if we're not discarding. Also, that means we don't have to check otherwise as well :)
 function Sorter:score(prompt, entry)
   if not entry or not entry.ordinal then return -1 end
-  return self:scoring_function(prompt or "", entry.ordinal, entry)
+
+  local ordinal = entry.ordinal
+
+  if self:_was_discarded(prompt, ordinal) then
+    return FILTERED
+  end
+
+  local score = self:scoring_function(prompt or "", ordinal, entry)
+
+  if score == FILTERED then
+    self:_mark_discarded(prompt, ordinal)
+  end
+
+  return score
+end
+
+function Sorter:_was_discarded(prompt, ordinal)
+  return self.discard and self._discard_state.filtered[ordinal]
+end
+
+function Sorter:_mark_discarded(prompt, ordinal)
+  if not self.discard then
+    return
+  end
+
+  self._discard_state.filtered[ordinal] = true
 end
 
 function sorters.new(...)
@@ -313,6 +371,8 @@ sorters.get_fzy_sorter = function()
   local OFFSET = -fzy.get_score_floor()
 
   return sorters.Sorter:new{
+    discard = true,
+
     scoring_function = function(_, prompt, line)
       -- Check for actual matches before running the scoring alogrithm.
       if not fzy.has_match(prompt, line) then