[UPDATE][VIM] Factorise b:undo_ftplugin

Instead of re-writing the same condition each time, I put the function
in an autoload plugin instead (which is going to be loaded just about
every time I start writing code, but that's neither here nor there) to
stop repeating myself.

vim/.vim/after/ftplugin/bash.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Use shfmt as ALE fixer for bash
 let b:ale_fixers=[ 'shfmt' ]

vim/.vim/after/ftplugin/c.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " More warnings and the usual version in flags for Clang
 let b:ale_c_clang_options='-Wall -Wextra -pedantic -std=c99'

vim/.vim/after/ftplugin/cpp.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " More warnings and the usual version in flags for Clang
 let b:ale_cpp_clang_options='-Wall -Wextra -pedantic -std=c++17'

vim/.vim/after/ftplugin/d.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Use my desired ALE fixer for D
 let b:ale_fixers=[ 'dfmt' ]

vim/.vim/after/ftplugin/fugitive.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Don't highlight trailing whitespace in fugitive windows
 let b:better_whitespace_enabled=0

vim/.vim/after/ftplugin/gitcommit.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Enable spell checking on commit messages
 setlocal spell

vim/.vim/after/ftplugin/json.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Use my desired ALE fixer for JSON
 let b:ale_fixers=[ 'jq' ]

vim/.vim/after/ftplugin/make.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Makefiles should use tabs to indent
 setlocal noexpandtab

vim/.vim/after/ftplugin/netrw.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Don't show Netrw in buffer list
 setlocal bufhidden=delete

vim/.vim/after/ftplugin/pandoc.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Let ALE know that I want Markdown linters
 let b:ale_linter_aliases=[ 'markdown' ]

vim/.vim/after/ftplugin/python.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Use my desired ALE fixers for python
 let b:ale_fixers=[ 'black', 'isort' ]

vim/.vim/after/ftplugin/qf.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Use h/l to go to the previous/next non-empty quickfix or location list
 nnoremap <silent> <buffer> h :call quickfixed#older()<CR>

vim/.vim/after/ftplugin/rust.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Check tests too
 let b:ale_rust_cargo_check_tests=1

vim/.vim/after/ftplugin/sh.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Use shfmt as ALE fixer for sh
 let b:ale_fixers=[ 'shfmt' ]

vim/.vim/after/ftplugin/zsh.vim

@@ -1,6 +1,5 @@
-if !exists("b:undo_ftplugin")
-    let b:undo_ftplugin=''
-endif
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+call ftplugined#check_undo_ft()
 
 " Use shfmt as ALE fixer for zsh
 let b:ale_fixers=[ 'shfmt' ]

vim/.vim/autoload/ftplugined.vim

@@ -0,0 +1,6 @@
+" Create the `b:undo_ftplugin` variable if it doesn't exist
+function! ftplugined#check_undo_ft()
+    if !exists("b:undo_ftplugin")
+        let b:undo_ftplugin=''
+    endif
+endfunction