auto merge of #19095 : juxiliary/rust/master, r=bstrie

Vim plugins shouldn't override user settings unless they ask!

Stops the plugin from modifying the users settings by default
instead makes them opt-in with `g:rust_recommended_style`

src/etc/vim/doc/rust.txt

@@ -53,6 +53,15 @@ g:rust_conceal_pub~
 	    let g:rust_conceal_pub = 1
 <
 
+                                                     *g:rust_recommended_style*
+g:rust_recommended_style~
+        Set this option to enable vim indentation and textwidth settings to
+        conform to style conventions of the rust standard library (i.e. use 4
+        spaces for indents and sets 'textwidth' to 99). This option is enabled
+	by default. To disable it: >
+	    let g:rust_recommended_style = 0
+<
+
                                                                  *g:rust_fold*
 g:rust_fold~
 	Set this option to turn on |folding|: >

src/etc/vim/ftplugin/rust.vim

@@ -35,9 +35,10 @@ silent! setlocal formatoptions+=j
 " otherwise it's better than nothing.
 setlocal smartindent nocindent
 
-setlocal tabstop=4 shiftwidth=4 softtabstop=4 expandtab
-
-setlocal textwidth=99
+if !exists("g:rust_recommended_style") || g:rust_recommended_style == 1
+	setlocal tabstop=4 shiftwidth=4 softtabstop=4 expandtab
+	setlocal textwidth=99
+endif
 
 " This includeexpr isn't perfect, but it's a good start
 setlocal includeexpr=substitute(v:fname,'::','/','g')