Implement middle fuzzy matching

Fixes #1422

doc/cmp.txt

@@ -451,7 +451,7 @@ confirmation.get_commit_characters~
   You can append or exclude commitCharacters via this configuration option
   function. The commitCharacters are defined by the LSP spec.
 
-                                                  *cmp-config.formatting.expandable_indicator*
+                                    *cmp-config.formatting.expandable_indicator*
 formatting.expandable_indicator~
   `cmp.expandable_indicator`
   Boolean to show the `~` expandable indicator in cmp's floating window.
@@ -474,6 +474,10 @@ matching.disallow_fuzzy_matching~
   `boolean`
   Whether to allow fuzzy matching.
 
+                           *cmp-config.matching.disallow_partial_fuzzy_matching*
+matching.disallow_partial_fuzzy_matching~
+  `boolean`
+  Whether to allow fuzzy matching without prefix matching.
                                  *cmp-config.matching.disallow_partial_matching*
 matching.disallow_partial_matching~
   `boolean`

lua/cmp/config/default.lua

@@ -50,6 +50,7 @@ return function()
 
     matching = {
       disallow_fuzzy_matching = false,
+      disallow_partial_fuzzy_matching = true,
       disallow_partial_matching = false,
       disallow_prefix_unmatching = false,
     },

lua/cmp/entry.lua

@@ -365,11 +365,13 @@ entry.match = function(self, input, matching_config)
     input,
     self.resolved_completion_item and '1' or '0',
     matching_config.disallow_fuzzy_matching and '1' or '0',
+    matching_config.disallow_partial_fuzzy_matching and '1' or '0',
     matching_config.disallow_partial_matching and '1' or '0',
     matching_config.disallow_prefix_unmatching and '1' or '0',
   }, function()
     local option = {
       disallow_fuzzy_matching = matching_config.disallow_fuzzy_matching,
+      disallow_partial_fuzzy_matching = matching_config.disallow_partial_fuzzy_matching,
       disallow_partial_matching = matching_config.disallow_partial_matching,
       disallow_prefix_unmatching = matching_config.disallow_prefix_unmatching,
       synonyms = {

lua/cmp/matcher.lua

@@ -78,7 +78,7 @@ end
 ---Match entry
 ---@param input string
 ---@param word string
----@param option { synonyms: string[], disallow_fuzzy_matching: boolean, disallow_partial_matching: boolean, disallow_prefix_unmatching: boolean }
+---@param option { synonyms: string[], disallow_fuzzy_matching: boolean, disallow_partial_fuzzy_matching: boolean, disallow_partial_matching: boolean, disallow_prefix_unmatching: boolean }
 ---@return integer
 matcher.match = function(input, word, option)
   option = option or {}
@@ -179,8 +179,10 @@ matcher.match = function(input, word, option)
   -- Check remaining input as fuzzy
   if matches[#matches].input_match_end < #input then
     if not option.disallow_fuzzy_matching then
-      if prefix and matcher.fuzzy(input, word, matches) then
-        return score, matches
+      if not option.disallow_partial_fuzzy_matching or prefix then
+        if  matcher.fuzzy(input, word, matches) then
+          return score, matches
+        end
       end
     end
     return 0, {}

lua/cmp/matcher_spec.lua

@@ -33,6 +33,9 @@ describe('matcher', function()
 
     assert.is.truthy(matcher.match('true', 'v:true', { synonyms = { 'true' } }) == matcher.match('true', 'true'))
     assert.is.truthy(matcher.match('g', 'get', { synonyms = { 'get' } }) > matcher.match('g', 'dein#get', { 'dein#get' }))
+
+    assert.is.truthy(matcher.match('Unit', 'net.UnixListener', { disallow_partial_fuzzy_matching = true }) == 0)
+    assert.is.truthy(matcher.match('Unit', 'net.UnixListener', { disallow_partial_fuzzy_matching = false }) >= 1)
   end)
 
   it('disallow_fuzzy_matching', function()

lua/cmp/types/cmp.lua

@@ -125,6 +125,7 @@ cmp.ItemField = {
 
 ---@class cmp.MatchingConfig
 ---@field public disallow_fuzzy_matching boolean
+---@field public disallow_partial_fuzzy_matching boolean
 ---@field public disallow_partial_matching boolean
 ---@field public disallow_prefix_unmatching boolean