add custom genericizer function

.vim/filetype.vim

@@ -118,4 +118,8 @@ autocmd FileType java let b:auto_trim_whitespace=1
 
 augroup templates
   autocmd BufNewFile *.vue 0r ~/.vim/skeletons/skeleton.vue
-augroup END
+augroup end
+
+augroup rust
+  autocmd FileType rust nnoremap <Leader>lg <cmd>lua rust_where_at_line()<CR>
+augroup end

.vim/nvim.lua

@@ -273,3 +273,55 @@ git_grep_word = function(conf)
   for k,v in pairs(conf) do opt[k] = v end
   builtin.grep_string(opt)
 end
+
+
+function string.insert(str1, str2, pos)
+    return str1:sub(1,pos)..str2..str1:sub(pos+1)
+end
+
+function string.split(s, delimiter)
+    result = {};
+    for match in (s..delimiter):gmatch("(.-)"..delimiter) do
+        table.insert(result, match);
+    end
+    return result;
+end
+
+local function rust_whereify_line(line, var_name)
+  if string.find(line, "fn") == nil then
+    return nil
+  end
+
+  local paren = string.find(line, "%(")
+  if paren == nil then return nil end
+
+  local open_generic = string.find(line, "<")
+  if open_generic ~= nil then
+    if open_generic < paren then
+      -- TODO(barakmich): it's already generic, we need to do something for that
+      -- probably a different function
+      return nil
+    end
+    -- just continue otherwise
+  end
+
+  local whitespace = string.match(line, "^(%s*)")
+
+  local generic = "<"..var_name..">"
+  local out = string.insert(line, generic, paren - 1)
+
+  local brace = string.find(out, "%{")
+  if brace == nil then brace = string.len(out) end
+
+  out = string.insert(out, "\n"..whitespace.."where\n"..whitespace.." "..var_name..": ,\n"..whitespace, brace - 1)
+
+  return string.split(out, "\n")
+end
+
+function rust_where_at_line()
+  local var_name = vim.fn.input("Variable: ")
+  local lineNum, col = unpack(vim.api.nvim_win_get_cursor(0))
+  local replacements = rust_whereify_line(vim.api.nvim_get_current_line(), var_name)
+  vim.api.nvim_buf_set_lines(0, lineNum-1, lineNum, false, replacements)
+  vim.api.nvim_win_set_cursor(0, {lineNum + 2, 4})
+end