From 2c20e459fafbf7f571833ce9a26143878c4f5902 Mon Sep 17 00:00:00 2001
From: Tom Ryder <tom@sanctum.geek.nz>
Date: Fri, 31 May 2019 22:02:49 +1200
Subject: Handle :cd then buffer write of non-existent path

---
 autoload/write_mkpath.vim | 52 +++++++++++++++++++++++++++++++++++++++++------
 plugin/write_mkpath.vim   |  4 +++-
 2 files changed, 49 insertions(+), 7 deletions(-)

diff --git a/autoload/write_mkpath.vim b/autoload/write_mkpath.vim
index 0d3e357..aca49f1 100644
--- a/autoload/write_mkpath.vim
+++ b/autoload/write_mkpath.vim
@@ -1,13 +1,42 @@
-function! write_mkpath#(path) abort
+" Handle a buffer created for a new file; anchor its filename to be absolute
+" if it's relative and the directory path doesn't yet exist; this stops Vim
+" trying to save in the wrong place if the user changes directory before
+" writing the buffer
+function! write_mkpath#New(path) abort
 
-  " Path exists, we don't need to do anything
-  if isdirectory(a:path)
+  " We don't have fnameescape(); this old Vim < v7.1.299 is likely too buggy
+  " to handle the buffer renaming for paths safely, so better not to mess with
+  " it and instead to stick with suboptimal but consistent behaviour
+  if !exists('*fnameescape')
     return
   endif
 
-  " If :write! was issued, we'll try to create the path; failing that, if
-  " 'confirm' is enabled, and the user responds affirmatively to the prompt,
-  " that will do, too.  Otherwise, we will allow the write to fail.
+  " Path exists, or is absolute; we don't need to do anything
+  if isdirectory(fnamemodify(a:path, ':h'))
+        \ || s:Absolute(a:path)
+    return
+  endif
+
+  " Set filename to absolute path using :file {name}
+  execute 'file '.fnameescape(getcwd().'/'.a:path)
+
+endfunction
+
+" Handle a :write operation; prompt for directory creation if needed with
+" 'confirm', force it with :write!
+function! write_mkpath#Write(path) abort
+
+  " Get all directory elements leading up to directory
+  let dir = fnamemodify(a:path, ':h')
+
+  " Directory exists, we don't need to do anything
+  if isdirectory(dir)
+    return
+  endif
+
+  " If :write! was issued, we'll try to create the missing path; failing that,
+  " if 'confirm' is enabled, and the user responds affirmatively to the
+  " prompt, that will do, too.  Otherwise, we will allow the write to fail.
   if v:cmdbang
     let mkpath = 1
   elseif &confirm
@@ -22,3 +51,14 @@ function! write_mkpath#(path) abort
   endif
 
 endfunction
+
+" Clumsy and probably wrong helper function to check if a path is absolute
+function! s:Absolute(path) abort
+  if has('unix')
+    return a:path =~# '^/'    " Leading slash on Unix
+  elseif has('win32') || has('win64')
+    return a:path =~# '^\u:'  " e.g. C: -- I'm not sure this is right
+  else
+    echoerr 'Unrecognised operating system'
+  endif
+endfunction
diff --git a/plugin/write_mkpath.vim b/plugin/write_mkpath.vim
index 334f24e..c7c9543 100644
--- a/plugin/write_mkpath.vim
+++ b/plugin/write_mkpath.vim
@@ -12,6 +12,8 @@ endif
 " Check path to every file before it's saved
 augroup write_mkpath
   autocmd!
+  autocmd BufNewFile *
+        \ call write_mkpath#New(expand('<afile>'))
   autocmd BufWritePre *
-        \ call write_mkpath#(expand('<afile>:p:h'))
+        \ call write_mkpath#Write(expand('<afile>'))
 augroup END
-- 
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