feat(filetype): add fast option for faster filetype detection

runtime/doc/lua.txt

@@ -2848,6 +2848,10 @@ vim.filetype.match({args})                              *vim.filetype.match()*
                 • {contents}? (`string[]`) An array of lines representing file
                   contents to use for matching. Can be used with {filename}.
                   Mutually exclusive with {buf}.
+                • {fast}? (`boolean`) Whether to skip time consuming detection
+                  steps, like pattern and content matching. Makes detection
+                  significantly faster at the cost of slightly fewer filetypes
+                  detected.
 
     Return (multiple): ~
         (`string?`) If a match was found, the matched filetype.

runtime/doc/news.txt

@@ -206,6 +206,7 @@ LSP
 LUA
 
 • |vim.fs.rm()| can delete files and directories.
+• |vim.filetype.match()| now takes `fast` option to perform fast detection.
 • |vim.validate()| now has a new signature which uses less tables,
   is more peformant and easier to read.
 • |vim.str_byteindex()| and |vim.str_utfindex()| gained overload signatures
@@ -218,7 +219,7 @@ OPTIONS
 
 PERFORMANCE
 
-• TODO
+• |vim.filetype.match()| overall performance is improved.
 
 PLUGINS
 

runtime/lua/vim/filetype.lua

@@ -2704,6 +2704,11 @@ end
 --- matching. Can be used with {filename}. Mutually exclusive
 --- with {buf}.
 --- @field contents? string[]
+---
+--- Whether to skip time consuming detection steps, like
+--- pattern and content matching. Makes detection significantly
+--- faster at the cost of slightly fewer filetypes detected.
+--- @field fast? boolean
 
 --- Perform filetype detection.
 ---
@@ -2750,6 +2755,7 @@ function M.match(args)
   local bufnr = args.buf
   local name = args.filename
   local contents = args.contents
+  local not_fast = not args.fast
 
   if bufnr and not name then
     name = api.nvim_buf_get_name(bufnr)
@@ -2778,8 +2784,10 @@ function M.match(args)
     -- Next, check the file path against available patterns with non-negative priority
     -- Cache match results of all parent patterns to improve performance
     local parent_matches = {}
-    ft, on_detect =
-      match_pattern_sorted(name, path, tail, pattern_sorted_pos, parent_matches, bufnr)
+    if not_fast then
+      ft, on_detect =
+        match_pattern_sorted(name, path, tail, pattern_sorted_pos, parent_matches, bufnr)
+    end
     if ft then
       return ft, on_detect
     end
@@ -2794,15 +2802,17 @@ function M.match(args)
     end
 
     -- Next, check patterns with negative priority
-    ft, on_detect =
-      match_pattern_sorted(name, path, tail, pattern_sorted_neg, parent_matches, bufnr)
+    if not_fast then
+      ft, on_detect =
+        match_pattern_sorted(name, path, tail, pattern_sorted_neg, parent_matches, bufnr)
+    end
     if ft then
       return ft, on_detect
     end
   end
 
   -- Finally, check file contents
-  if contents or bufnr then
+  if not_fast and (contents or bufnr) then
     if contents == nil then
       assert(bufnr)
       if api.nvim_buf_line_count(bufnr) > 101 then

test/functional/lua/filetype_spec.lua

@@ -128,6 +128,44 @@ describe('vim.filetype', function()
     )
   end)
 
+  it('can be fast', function()
+    eq(
+      exec_lua(function()
+        return vim.filetype.match({ filename = 'init.lua', fast = true })
+      end),
+      'lua'
+    )
+    eq(
+      exec_lua(function()
+        return vim.filetype.match({ filename = 'Dockerfile', fast = true })
+      end),
+      'dockerfile'
+    )
+
+    -- Pattern and content matching should be skipped
+    eq(
+      exec_lua(function()
+        return {
+          no_fast = vim.filetype.match({ filename = '/etc/a2ps/top-secret.cfg' }),
+          yes_fast = vim.filetype.match({ filename = '/etc/a2ps/top-secret.cfg', fast = true }),
+        }
+      end),
+      { no_fast = 'a2ps', yes_fast = nil }
+    )
+
+    eq(
+      exec_lua(function()
+        local buf = vim.api.nvim_create_buf(false, true)
+        vim.api.nvim_buf_set_lines(buf, 0, -1, false, { '" vim' })
+        return {
+          no_fast = vim.filetype.match({ buf = buf }),
+          yes_fast = vim.filetype.match({ buf = buf, fast = true }),
+        }
+      end),
+      { no_fast = 'vim', yes_fast = nil }
+    )
+  end)
+
   it('considers extension mappings when matching from hashbang', function()
     eq(
       'fooscript',