autocmd for markdown textwidth=100 failing

Question

I want to set my markdown files to have textwidth=100 but cannot get it working. The strange thing is that it works sometimes and sometimes not. My autocmd is:

augroup auFileTypes
  autocmd! auFileTypes
  audocmd BufNewFile,BufRead *.md set filetype=markdown | setlocal textwidth=100
augroup end

Some files (such as create_template.md or index.md) just work; some files (such as completed_jobs.md or issues.md) don't work.

I thought at first it might be a "sequencing" problem such as every other one works, but that turned out not to be the case.

I'm on version 8.1-650, via Homebrew.

UPDATE: When I load the file completed_jobs.md, :setlocal says this:

--- Local option values ---
  autoindent          cryptmethod=        errorformat=        grepprg=            linebreak           number              scroll=33           sidescrolloff=-1    syntax=markdown
--autoread            cursorline          expandtab           include=            lispwords=          path=               scrolloff=-1        softtabstop=2       tabstop=2
  backupcopy=         define=             filetype=markdown   keywordprg=         makeprg=            relativenumber      shiftwidth=2      noswapfile            tagcase=
  cinkeys=0{,0},0),:,0#,!^F,o,O,e
  comments=fb:*,fb:-,fb:+,n:>
  commentstring=<!--%s-->
  fileencoding=utf-8
  formatlistpat=^\s*\d\+\.\s\+\|^[-*+]\s\+\|^\[^\ze[^\]]\+\]:
  indentkeys=0{,0},:,0#,!^F,o,O,e
  iskeyword=@,48-57,_,192-255,$
  tags=./tags,tags,~/workspace/automation-ui-core-etap/tags
  undolevels=-123456

and `onboarding.md :setlocal says this:

--- Local option values ---
  autoindent          cryptmethod=      noendofline           filetype=markdown   keywordprg=         makeprg=            relativenumber      shiftwidth=2      noswapfile            tagcase=
--autoread            cursorline          errorformat=        grepprg=            linebreak           number              scroll=33           sidescrolloff=-1    syntax=markdown     textwidth=100
  backupcopy=         define=             expandtab           include=            lispwords=          path=               scrolloff=-1        softtabstop=2       tabstop=2
  cinkeys=0{,0},0),:,0#,!^F,o,O,e
  comments=fb:*,fb:-,fb:+,n:>
  commentstring=<!--%s-->
  fileencoding=utf-8
  formatoptions=tcqln
  formatlistpat=^\s*\d\+\.\s\+\|^[-*+]\s\+\|^\[^\ze[^\]]\+\]:
  indentkeys=0{,0},:,0#,!^F,o,O,e
  iskeyword=@,48-57,_,192-255,58,-,$
  tags=./tags,tags,~/workspace/automation-ui-core-etap/tags
  undolevels=-123456

Only difference I can see (besides the missing textwidth=100) is the noendofline setting. However, even that is not consistent across the various successes and failures.

Answer 1

Files matching *.md are detected as markdown. The extension md was removed from Modula and "given" to Markdown. So you don't need to act on file extensions, but you can use the FileType event.

Change your vimrc to contain:

augroup auFileTypes
  autocmd!
  autocmd FileType markdown setlocal textwidth=100
augroup end

This autocommand is executed when the file type "markdown" is detected.

If this doesn't work as expected, reduce your Vim setup to only contain the four lines above and test. Then slowly build up your Vim setup again, until you find the part that interferes with above autocommands.

---

As statox mentioned in the comments, there is a defined way to activate filetype specific settings, by creating a file in the directory ~/.vim/after/ftplugin with the file name like the file type (~/.vim/after/ftplugin/markdown.vim).

I have to admit, that if you only want to change one option, this is oversized.