Trigger BufRead when a plugin is loaded by `on` condition

Close #489

plug.vim

@@ -397,7 +397,9 @@ function! s:reorg_rtp()
 endfunction
 
 function! s:doautocmd(...)
-  execute 'doautocmd' ((v:version > 703 || has('patch442')) ? '<nomodeline>' : '') join(a:000)
+  if exists('#'.join(a:000, '#'))
+    execute 'doautocmd' ((v:version > 703 || has('patch442')) ? '<nomodeline>' : '') join(a:000)
+  endif
 endfunction
 
 function! plug#load(...)
@@ -415,9 +417,7 @@ function! plug#load(...)
   for name in a:000
     call s:lod([name], ['ftdetect', 'after/ftdetect', 'plugin', 'after/plugin'])
   endfor
-  if exists('#BufRead')
-    doautocmd BufRead
-  endif
+  call s:doautocmd('BufRead')
   return 1
 endfunction
 
@@ -453,9 +453,7 @@ function! s:lod(names, types, ...)
       endif
       call s:source(rtp, a:2)
     endif
-    if exists('#User#'.name)
-      call s:doautocmd('User', name)
-    endif
+    call s:doautocmd('User', name)
   endfor
 endfunction
 
@@ -463,21 +461,19 @@ function! s:lod_ft(pat, names)
   let syn = 'syntax/'.a:pat.'.vim'
   call s:lod(a:names, ['plugin', 'after/plugin'], syn, 'after/'.syn)
   execute 'autocmd! PlugLOD FileType' a:pat
-  if exists('#filetypeplugin#FileType')
-    doautocmd filetypeplugin FileType
-  endif
-  if exists('#filetypeindent#FileType')
-    doautocmd filetypeindent FileType
-  endif
+  call s:doautocmd('filetypeplugin', 'FileType')
+  call s:doautocmd('filetypeindent', 'FileType')
 endfunction
 
 function! s:lod_cmd(cmd, bang, l1, l2, args, names)
   call s:lod(a:names, ['ftdetect', 'after/ftdetect', 'plugin', 'after/plugin'])
+  call s:doautocmd('BufRead')
   execute printf('%s%s%s %s', (a:l1 == a:l2 ? '' : (a:l1.','.a:l2)), a:cmd, a:bang, a:args)
 endfunction
 
 function! s:lod_map(map, names, prefix)
   call s:lod(a:names, ['ftdetect', 'after/ftdetect', 'plugin', 'after/plugin'])
+  call s:doautocmd('BufRead')
   let extra = ''
   while 1
     let c = getchar(0)

test/regressions.vader

@@ -7,13 +7,13 @@ Execute (#112 On-demand loading should not suppress messages from ftplugin):
   redir => out
   tabnew a.c
   redir END
-  Assert stridx(out, 'ftplugin') >= 0
+  Assert stridx(out, 'ftplugin-c') >= 0
 
 * The same applies to plug#load())
   redir => out
   call plug#load('ftplugin-msg')
   redir END
-  Assert stridx(out, 'ftplugin') >= 0
+  Assert stridx(out, 'ftplugin-c') >= 0
   q
 
 
@@ -302,3 +302,16 @@ Execute (#474: Load ftdetect files in filetypedetect augroup):
   AssertEqual 'rust', &filetype
   Log &filetype
   bd
+
+**********************************************************************
+Execute (#489 On-demand loading with 'on' option should trigger BufRead autocmd):
+  call plug#begin('$PLUG_FIXTURES')
+  Plug 'ftplugin-msg', { 'on': 'XXX' }
+  call plug#end()
+
+  tabnew a.java
+  redir => out
+  silent! XXX
+  redir END
+  Assert stridx(out, 'ftplugin-java') >= 0
+  q

test/run

@@ -2,6 +2,7 @@
 
 cd $(dirname "${BASH_SOURCE[0]}")
 
+export HOME=/tmp
 export BASE="$PWD"
 export PLUG_SRC="$PWD/../plug.vim"
 export PLUG_FIXTURES="$PWD/fixtures"
@@ -77,7 +78,8 @@ DOC
 
   rm -rf "$PLUG_FIXTURES/ftplugin-msg"
   mkdir -p "$PLUG_FIXTURES/ftplugin-msg/ftplugin"
-  echo "echomsg 'ftplugin'" > "$PLUG_FIXTURES/ftplugin-msg/ftplugin/c.vim"
+  echo "echomsg 'ftplugin-c'" > "$PLUG_FIXTURES/ftplugin-msg/ftplugin/c.vim"
+  echo "echomsg 'ftplugin-java'" > "$PLUG_FIXTURES/ftplugin-msg/ftplugin/java.vim"
 
   rm -rf /tmp/new-branch
   cd /tmp