Add DirvishShdoCreated autocmd

Allow users to process shdo scripts on creation.

The example from the doc is especially useful with 'autochdir' so
scripts start in the current dirvish working directory. Other users may
tend to create scripts with arguments, want their commands to be inside
a function, or output some diagnostic data.

Using the same escaping that is applied on lines since that seems like
the safest thing to do.

dirvish_dummy_events ensures no error if users haven't setup an autocmd.

Author: idbrii

autoload/dirvish.vim

@@ -5,6 +5,11 @@ let s:noau       = 'silent noautocmd keepjumps'
 let s:cb_map = {}   " callback map
 let s:rel = get(g:, 'dirvish_relative_paths', 0)
 
+augroup dirvish_dummy_events
+  autocmd!
+  autocmd User Dirvish* "
+augroup END
+
 " Debug:
 "     echo '' > dirvish.log ; tail -F dirvish.log
 "     nvim +"let g:dirvish_dbg=1" -- b1 b2
@@ -169,6 +174,9 @@ func! dirvish#shdo(paths, cmd) abort
   augroup END
 
   nnoremap <buffer><silent> Z! :silent write<Bar>exe '!'.(has('win32')?fnameescape(escape(expand('%:p:gs?\\?/?'), '&\')):join(map(split(&shell), 'shellescape(v:val)')).' %')<Bar>if !v:shell_error<Bar>close<Bar>endif<CR>
+
+  let b:dirvish_dir = escape(shellescape(head),'&\')
+  doautocmd <nomodeline> User DirvishShdoCreated
 endf
 
 " Returns true if the buffer was modified by the user.

doc/dirvish.txt

@@ -126,6 +126,28 @@ dirvish#remove_icon_fn(fn_id)
     Unregisters the function associated with {fn_id} returned from
     |dirvish#add_icon_fn()|.
 
+==============================================================================
+AUTOCOMMANDS                                            *dirvish-autocommands*
+
+DirvishShdoCreated                                   *User_DirvishShdoCreated*
+    A |User| |autocommand| invoked after creating a |:Shdo| buffer.
+    b:dirvish_dir is set to the previous Dirvish buffer's path.
+
+    To ensure scripts always cd to the current dirvish directory, you could
+    add this to your vimrc: >
+
+    autocmd User DirvishShdoCreated call OnShdoCreated()
+    function! OnShdoCreated() abort
+        if has('win32')
+            " work across hard drives
+            let chdir = 'pushd '
+        else
+            let chdir = 'cd '
+        endif
+        call append(0, [chdir .. b:dirvish_dir, ''])
+    endf
+<
+
 ==============================================================================
 OPTIONS                                                      *dirvish-options*