neovim: add H keybinding to switch between matching .c and .h files

hosts/common/programs/neovim/plugins.nix

@@ -244,6 +244,10 @@ with pkgs.vimPlugins;
     type = "lua";
     config = builtins.readFile ./nix_shell.lua;
   }
+  {
+    type = "viml";
+    config = builtins.readFile ./source_nav.vim;
+  }
   {
     # show commit which last modified text under the cursor.
     # trigger with `:GitMessenger` or `<Leader>gm` (i.e. `\gm`)

hosts/common/programs/neovim/source_nav.vim

@@ -0,0 +1,26 @@
+function GoToHeader()
+  let newfile = expand('%:r') . '.h'
+  execute "e " . fnameescape(l:newfile)
+endfunc
+function GoToSource()
+  let newfile = expand('%:r') . '.c'
+  execute "e " . fnameescape(l:newfile)
+endfunc
+function ToggleHeaderSource()
+  " If in abc.c file, open abc.h
+  " If in abc.h, open abc.c
+  let ext = expand('%:e')
+  if ext =~ 'c'
+    call GoToHeader()
+  else
+    call GoToSource()
+  end
+endfunc
+
+" command H call ToggleHeaderSource()
+" command C call ToggleHeaderSource()
+
+nmap H :call ToggleHeaderSource()<CR>
+
+" TODO: port to lua impl
+" vim.api.nvim_set_keymap("n", "H", "", { callback=ToggleHeaderSource, desc = "cycle between .h <-> .c files" })