Merge branch 'release/v8.24.0'v8.24.0

* release/v8.24.0:
  Use v:null in XDG-related contexts
  Add handling of "after" subdirs in Vim XDG config
  Separate cache runtime behaviour from config
  Tolerate unset iteration variables
  Improve "absolute path" check for XDG base dirs
  Tidy and correct XDG var getenv() fallback

2 files changed, 32 insertions, 13 deletions

diff --git a/vim/autoload/getenv.vim b/vim/autoload/getenv.vim
new file mode 100644
index 00000000..2b8fef1b
--- /dev/null
+++ b/vim/autoload/getenv.vim
@@ -0,0 +1,22 @@
+" Backport getenv() from v8.1.1305
+"
+" <https://github.com/vim/vim/releases/tag/v8.1.1305>
+"
+function! getenv#(name) abort
+
+  " Use native if available
+  if exists('*getenv')
+    return getenv(a:name)
+  endif
+
+  " Backport
+  if a:name !~# '^[A-Z][A-Z0-9_]*$'
+    throw 'Illegal env var name'
+  endif
+  let value = v:null
+  if exists('$'.a:name)
+    execute 'let value = $'.a:name
+  endif
+  return value
+
+endfunction
diff --git a/vim/autoload/xdg.vim b/vim/autoload/xdg.vim
index 2b1e7c56..2b90f5f1 100644
--- a/vim/autoload/xdg.vim
+++ b/vim/autoload/xdg.vim
@@ -11,28 +11,25 @@ let s:subdir = 'vim'
 
 function! s:Get(name) abort
   let name = a:name
-  if name !~# '^[A-Z][A-Z0-9_]*$'
-    throw 'Illegal env var name'
-  endif
-  let value = ''
-  execute 'let value = $'.name
-  if value !=# ''
-    return value
-  elseif has_key(s:defaults, name)
-    return s:defaults[name]
-  else
-    return ''
+  if !has_key(s:defaults, name)
+    throw 'Illegal XDG basedirs env var name'
   endif
+  let value = getenv#(name)
+  return value !=# v:null
+        \ ? value
+        \ : s:defaults[name]
 endfunction
 
 function! s:Absolute(path) abort
-  return a:path =~# '^[/~]'
+  return a:path =~# '^/'
+        \ || a:path =~# '^\~/'
+        \ || a:path ==# '~'
 endfunction
 
 function! s:Home(name) abort
   let home = s:Get(a:name)
   if !s:Absolute(home)
-    return ''
+    return v:null
   endif
   return join([home, s:subdir], '/')
 endfunction