vim: show tabs and expand them to spaces

modules/universal/env/home-manager.nix

@@ -455,6 +455,9 @@ in
             " copy/paste to system clipboard
             set clipboard=unnamedplus
 
+            " screw tabs; always expand them into spaces
+            set expandtab
+
             " at least don't open files with sections folded by default
             set nofoldenable
 
@@ -470,6 +473,12 @@ in
             " highlight trailing space & related syntax errors (doesn't seem to work??)
             " let c_space_errors=1
             " let python_space_errors=1
+
+            " enable highlighting of leading/trailing spaces,
+            " and especially tabs
+            " source: https://www.reddit.com/r/neovim/comments/chlmfk/highlight_trailing_whitespaces_in_neovim/
+            set list
+            set listchars=tab:▷\·,trail:·,extends:◣,precedes:◢,nbsp:○
           '';
         };