Add option for symbol matching logic. (#1515)

The no_symbol_match makes command line completion a lot less useful. It
disables any matches for file names with symbols in them. This prevents
completing things like ":b foo/bar" to ":b foo/bar.txt" or ":b foo_" to
":b baz/foo_bar.txt". Add an option `disallow_symbol_nonprefix_matching`
that prevents a match if it contains a symbol and isn't a prefix match.
Make that option the default. Add the option to documentation and tests.
Add to the examples for command line setup disabling the option.

lua/cmp/config/default.lua

@@ -57,6 +57,7 @@ return function()
       disallow_partial_fuzzy_matching = true,
       disallow_partial_matching = false,
       disallow_prefix_unmatching = false,
+      disallow_symbol_nonprefix_matching = true,
     },
 
     sorting = {

lua/cmp/entry.lua

@@ -360,12 +360,13 @@ end
 ---@param matching_config cmp.MatchingConfig
 ---@return { score: integer, matches: table[] }
 entry.match = function(self, input, matching_config)
-  return self.match_cache:ensure(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()
+  return self.match_cache:ensure(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') .. ':' .. (matching_config.disallow_symbol_nonprefix_matching 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,
+      disallow_symbol_nonprefix_matching = matching_config.disallow_symbol_nonprefix_matching,
       synonyms = {
         self:get_word(),
         self:get_completion_item().label,

lua/cmp/matcher.lua

@@ -73,12 +73,15 @@ end
 --     `,` -> print,
 --                 ~
 --      * Typically, the middle match with symbol characters only is false positive. should be ignored.
+--        This doesn't work for command line completions like ":b foo_" which we like to match
+--        "lib/foo_bar.txt". The option disallow_symbol_nonprefix_matching controls this and defaults
+--        to preventing matches like these. The documentation recommends it for command line completion.
 --
 --
 ---Match entry
 ---@param input string
 ---@param word string
----@param option { synonyms: string[], disallow_fullfuzzy_matching: boolean, disallow_fuzzy_matching: boolean, disallow_partial_fuzzy_matching: boolean, disallow_partial_matching: boolean, disallow_prefix_unmatching: boolean }
+---@param option { synonyms: string[], disallow_fullfuzzy_matching: boolean, disallow_fuzzy_matching: boolean, disallow_partial_fuzzy_matching: boolean, disallow_partial_matching: boolean, disallow_prefix_unmatching: boolean, disallow_symbol_nonprefix_matching: boolean }
 ---@return integer, table
 matcher.match = function(input, word, option)
   option = option or {}
@@ -160,7 +163,9 @@ matcher.match = function(input, word, option)
   end
 
   if no_symbol_match and not prefix then
-    return 0, {}
+    if option.disallow_symbol_nonprefix_matching then
+      return 0, {}
+    end
   end
 
   -- Compute prefix match score

lua/cmp/matcher_spec.lua

@@ -49,6 +49,7 @@ describe('matcher', function()
       disallow_partial_matching = false,
       disallow_prefix_unmatching = false,
       disallow_partial_fuzzy_matching = false,
+      disallow_symbol_nonprefix_matching = true,
     })
     assert.is.truthy(score >= 1)
     assert.equals(matches[1].word_match_start, 5)
@@ -58,6 +59,7 @@ describe('matcher', function()
       disallow_partial_matching = false,
       disallow_prefix_unmatching = false,
       disallow_partial_fuzzy_matching = true,
+      disallow_symbol_nonprefix_matching = true,
     })
     assert.is.truthy(score == 0)
   end)
@@ -84,6 +86,11 @@ describe('matcher', function()
     assert.is.truthy(matcher.match('bar', 'foo_bar', { disallow_prefix_unmatching = false }) >= 1)
   end)
 
+  it('disallow_symbol_nonprefix_matching', function()
+    assert.is.truthy(matcher.match('foo_', 'b foo_bar', { disallow_symbol_nonprefix_matching = true }) == 0)
+    assert.is.truthy(matcher.match('foo_', 'b foo_bar', { disallow_symbol_nonprefix_matching = false }) >= 1)
+  end)
+
   it('debug', function()
     matcher.debug = function(...)
       print(vim.inspect({ ... }))

lua/cmp/types/cmp.lua

@@ -137,6 +137,7 @@ cmp.ItemField = {
 ---@field public disallow_partial_fuzzy_matching boolean
 ---@field public disallow_partial_matching boolean
 ---@field public disallow_prefix_unmatching boolean
+---@field public disallow_symbol_nonprefix_matching boolean
 
 ---@class cmp.SortingConfig
 ---@field public priority_weight integer