feat: add fuzzy matching sorter experimentally

lua/frecency/picker.lua

@@ -108,7 +108,7 @@ function Picker:start(opts)
     prompt_title = "Frecency",
     finder = finder,
     previewer = config_values.file_previewer(opts),
-    sorter = sorters.get_substr_matcher(),
+    sorter = require "frecency.sorter",
     on_input_filter_cb = self:on_input_filter_cb(opts),
     attach_mappings = function(prompt_bufnr)
       return self:attach_mappings(prompt_bufnr)

lua/frecency/sorter.lua

@@ -0,0 +1,49 @@
+local sorters = require "telescope.sorters"
+
+---@type table<string, string[]>
+local regexp_cache = {}
+
+---@param prompt string
+local function regexps(prompt)
+  if not regexp_cache[prompt] then
+    ---@type string[]
+    local res = {}
+    for c in prompt:lower():gmatch "." do
+      local escaped = c:gsub([=[[%^%$%(%)%%%.%[%]%*%+%-%?]]=], "%%%0")
+      table.insert(res, escaped)
+    end
+    regexp_cache[prompt] = res
+  end
+  return regexp_cache[prompt]
+end
+
+return sorters.Sorter:new {
+  ---@param prompt string
+  ---@param display string
+  highlighter = function(_, prompt, display)
+    local converted = display:lower()
+    local res = regexps(prompt)
+    ---@type { start: number, finish: number }[]
+    local highlights = {}
+    local init = 1
+    for _, re in ipairs(res) do
+      local start, finish = converted:find(re, init)
+      if start and finish then
+        init = finish + 1
+        table.insert(highlights, { start = start, finish = finish })
+      end
+    end
+    return highlights
+  end,
+
+  ---@param prompt string
+  ---@param entry FrecencyEntry
+  scoring_function = function(_, prompt, _, entry)
+    if #prompt == 0 then
+      return 1
+    end
+    local res = regexps(prompt)
+    local display = entry.ordinal:lower()
+    return display:match(table.concat(res, ".*")) and entry.index or -1
+  end,
+}