環境

vim 8.2(Ubuntu 22.04)
(vim 8.1 では起きないかもしれません)

背景

~/.vimrc で

set nocp
set indentexpr=
set noautoindent
set nocindent                                                                                                                               set nosmartindent                                                                                                                             

filetype indent off 

au! BufNewFile,BufRead *.cc setl ts=2 sw=2 expandtab nocindent noautoindent nosmartindent                                                   au! BufNewFile,BufRead *.cpp setl ts=2 sw=2 expandtab nocindent noautoindent nosmartinden

としても, cpp ファイル(filetype=cpp と判定される)開くと常に cindent が設定され, 勝手にインデントされつらい...
(ts は設定変えると反映されるのに...)

原因

vim -V (verbose レベルを変えることができるが, デフォルトの 10 で十分)で cindent の設定を追うと,

...
autocommand setl ts=2 sw=2 expandtab nocindent noautoindent nosmartindent
Executing BufRead Autocommands for "*.cc"
autocommand if exists("cynlib_syntax_for_cc")|setf cynlib|else|setf cpp|endif
Executing FileType Autocommands for "*"
autocommand exe "set syntax=" . expand("<amatch>")
Executing Syntax Autocommands for "*"
autocommand call s:SynSet()
chdir(/usr/share/vim/vim82/syntax)
fchdir() to previous dir
line 25: sourcing "/usr/share/vim/vim82/syntax/cpp.vim"
chdir(/usr/share/vim/vim82/syntax)
fchdir() to previous dir
line 16: sourcing "/usr/share/vim/vim82/syntax/c.vim"
finished sourcing /usr/share/vim/vim82/syntax/c.vim
continuing in /usr/share/vim/vim82/syntax/cpp.vim
finished sourcing /usr/share/vim/vim82/syntax/cpp.vim
continuing in <SNR>4_SynSet
Executing Syntax Autocommands for "cpp"
autocommand if (exists('b:load_doxygen_syntax') && b:load_doxygen_syntax)^I|| (exists('g:load_doxygen_syntax') && g:load_doxygen_syntax)   | runtime! syntax/doxygen.vim | endif
Executing FileType Autocommands for "*"
autocommand call s:LoadFTPlugin()
chdir(/usr/share/vim/vim82/ftplugin)
fchdir() to previous dir
line 17: sourcing "/usr/share/vim/vim82/ftplugin/cpp.vim"
chdir(/usr/share/vim/vim82/ftplugin)
fchdir() to previous dir
line 12: sourcing "/usr/share/vim/vim82/ftplugin/c.vim"
finished sourcing /usr/share/vim/vim82/ftplugin/c.vim
continuing in /usr/share/vim/vim82/ftplugin/cpp.vim
finished sourcing /usr/share/vim/vim82/ftplugin/cpp.vim
continuing in <SNR>14_LoadFTPlugin
Executing FileType Autocommands for "*"
autocommand call s:LoadIndent()
chdir(/usr/share/vim/vim82/indent)
fchdir() to previous dir
line 14: sourcing "/usr/share/vim/vim82/indent/cpp.vim"
finished sourcing /usr/share/vim/vim82/indent/cpp.vim
...

autocomand BufRead の設定したあとに, /usr/share/vim/vim82/indent/cpp.vim で cindent が上書きされていました...
(setl を set にしても同様)

" Only load this indent file when no other was loaded.
if exists("b:did_indent")
   finish
endif
let b:did_indent = 1

" C++ indenting is built-in, thus this is very simple
setlocal cindent

解決 `BufEnter` も追加する

au! に BufEnter も必要でした!
(BufEnter だけでいいかも)

au! BufNewFile,BufRead,BufEnter *.cc setl ts=2 sw=2 expandtab nocindent noautoindent nosmartindent                                          au! BufNewFile,BufRead,BufEnter *.cpp setl ts=2 sw=2 expandtab nocindent noautoindent nosmartindent

...
Executing FileType Autocommands for "*"
autocommand call s:LoadIndent()
chdir(/usr/share/vim/vim82/indent)
fchdir() to previous dir
line 14: sourcing "/usr/share/vim/vim82/indent/cpp.vim"
finished sourcing /usr/share/vim/vim82/indent/cpp.vim
continuing in <SNR>15_LoadIndent
Executing BufRead Autocommands for "*"
autocommand if !did_filetype() && expand("<amatch>") !~ g:ft_ignore_pat | runtime! scripts.vim | endif
Executing BufRead Autocommands for "*"
autocommand if !did_filetype() && expand("<amatch>") !~ g:ft_ignore_pat    && (getline(1) =~ '^#' || getline(2) =~ '^#' || getline(3) =~ '^#'^I|| getline(4) =~ '^#' || getline(5) =~ '^#') |   setf FALLBACK conf | endif
Executing BufEnter Autocommands for "*.cc"
autocommand setl ts=2 sw=2 expandtab nocindent noautoindent nosmartindent
Executing BufEnter Autocommands for "*"
...

ident の設定を読み込んだあとに BufEnter で設定上書きしてくれました.
ややこしいですね...

バグ?

今回は .cc ファイルで filetype plugin が起動して indent ファイルを読んだことにより起こった... はず?

filetype indent off(filetype indent plugin off でも)だと, indent ファイルは読み込まないとあるのですけどね...
`

TODO

.vimrc でグローバルかつトップレベルで強制的に nocindent する方法を探す旅に出たい 🥺