Allow completion in the command-line window

README.md

@@ -2073,9 +2073,9 @@ Default: `[see next line]`
 ```viml
 let g:ycm_filetype_blacklist = {
       \ 'tagbar': 1,
-      \ 'qf': 1,
       \ 'notes': 1,
       \ 'markdown': 1,
+      \ 'netrw': 1,
       \ 'unite': 1,
       \ 'text': 1,
       \ 'vimwiki': 1,
@@ -3346,6 +3346,18 @@ more details.
 This is a Vim bug fixed in version 8.1.0256. Update your Vim to this version or
 later.
 
+### `TAB` is already mapped to trigger completion in the command-line window
+
+Vim automatically maps the key set by the `wildchar` option, which is `TAB` by
+default, to complete commands in the command-line window. If you would prefer
+using this key to cycle through YCM's suggestions without changing the value of
+`wildchar`, add the following to your vimrc:
+
+```viml
+autocmd CmdwinEnter * inoremap <expr><buffer> <TAB>
+      \ pumvisible() ? "\<C-n>" : "\<TAB>"
+```
+
 Contributor Code of Conduct
 ---------------------------
 

autoload/youcompleteme.vim

@@ -45,6 +45,11 @@ let s:pollers = {
       \     'wait_milliseconds': 100
       \   }
       \ }
+let s:buftype_blacklist = {
+      \   'help': 1,
+      \   'terminal': 1,
+      \   'quickfix': 1
+      \ }
 
 
 " When both versions are available, we prefer Python 3 over Python 2:
@@ -132,7 +137,7 @@ function! youcompleteme#Enable()
     " filetype) and if so, the FileType event has triggered before and thus the
     " buffer is already parsed.
     autocmd FileType * call s:OnFileTypeSet()
-    autocmd BufEnter * call s:OnBufferEnter()
+    autocmd BufEnter,CmdwinEnter * call s:OnBufferEnter()
     autocmd BufUnload * call s:OnBufferUnload()
     autocmd InsertLeave * call s:OnInsertLeave()
     autocmd VimLeave * call s:OnVimLeave()
@@ -428,23 +433,23 @@ endfunction
 
 
 function! s:AllowedToCompleteInBuffer( buffer )
-  let buffer_filetype = getbufvar( a:buffer, '&filetype' )
+  let buftype = getbufvar( a:buffer, '&buftype' )
 
-  if empty( buffer_filetype ) ||
+  if has_key( s:buftype_blacklist, buftype )
-        \ getbufvar( a:buffer, '&buftype' ) ==# 'nofile' ||
-        \ buffer_filetype ==# 'qf'
     return 0
   endif
 
-  if s:DisableOnLargeFile( a:buffer )
+  let filetype = getbufvar( a:buffer, '&filetype' )
+
+  if empty( filetype ) || s:DisableOnLargeFile( a:buffer )
     return 0
   endif
 
   let whitelist_allows = type( g:ycm_filetype_whitelist ) != type( {} ) ||
         \ has_key( g:ycm_filetype_whitelist, '*' ) ||
-        \ has_key( g:ycm_filetype_whitelist, buffer_filetype )
+        \ has_key( g:ycm_filetype_whitelist, filetype )
   let blacklist_allows = type( g:ycm_filetype_blacklist ) != type( {} ) ||
-        \ !has_key( g:ycm_filetype_blacklist, buffer_filetype )
+        \ !has_key( g:ycm_filetype_blacklist, filetype )
 
   let allowed = whitelist_allows && blacklist_allows
   if allowed
@@ -528,6 +533,13 @@ endfunction
 
 
 function! s:OnFileTypeSet()
+  " The contents of the command-line window are empty when the filetype is set
+  " for the first time. Users should never change its filetype so we only rely
+  " on the CmdwinEnter event for that window.
+  if !empty( getcmdwintype() )
+    return
+  endif
+
   if !s:AllowedToCompleteInCurrentBuffer()
     return
   endif

doc/youcompleteme.txt

@@ -181,6 +181,7 @@ module could not be loaded" |youcompleteme-on-windows-i-get-e887-sorry-this-comm
   35. YCM does not shut down when I quit Vim |youcompleteme-ycm-does-not-shut-down-when-i-quit-vim|
   36. YCM does not work with my Anaconda Python setup |youcompleteme-ycm-does-not-work-with-my-anaconda-python-setup|
   37. Automatic import insertion after selecting a completion breaks undo |youcompleteme-automatic-import-insertion-after-selecting-completion-breaks-undo|
+  38. 'TAB' is already mapped to trigger completion in the command-line window |youcompleteme-tab-is-already-mapped-to-trigger-completion-in-command-line-window|
  14. Contributor Code of Conduct    |youcompleteme-contributor-code-of-conduct|
  15. Contact                                            |youcompleteme-contact|
  16. License                                            |youcompleteme-license|
@@ -2331,9 +2332,9 @@ Default: '[see next line]'
 >
   let g:ycm_filetype_blacklist = {
         \ 'tagbar': 1,
-        \ 'qf': 1,
         \ 'notes': 1,
         \ 'markdown': 1,
+        \ 'netrw': 1,
         \ 'unite': 1,
         \ 'text': 1,
         \ 'vimwiki': 1,
@@ -3601,6 +3602,18 @@ Automatic import insertion after selecting a completion breaks undo ~
 This is a Vim bug fixed in version 8.1.0256. Update your Vim to this version or
 later.
 
+-------------------------------------------------------------------------------
+*youcompleteme-tab-is-already-mapped-to-trigger-completion-in-command-line-window*
+'TAB' is already mapped to trigger completion in the command-line window ~
+
+Vim automatically maps the key set by the 'wildchar' option, which is 'TAB' by
+default, to complete commands in the command-line window. If you would prefer
+using this key to cycle through YCM's suggestions without changing the value of
+'wildchar', add the following to your vimrc:
+>
+  autocmd CmdwinEnter * inoremap <expr><buffer> <TAB>
+        \ pumvisible() ? "\<C-n>" : "\<TAB>"
+<
 ===============================================================================
                                     *youcompleteme-contributor-code-of-conduct*
 Contributor Code of Conduct ~

plugin/youcompleteme.vim

@@ -91,7 +91,6 @@ let g:ycm_filetype_whitelist =
 let g:ycm_filetype_blacklist =
       \ get( g:, 'ycm_filetype_blacklist', {
       \   'tagbar': 1,
-      \   'qf': 1,
       \   'notes': 1,
       \   'markdown': 1,
       \   'netrw': 1,