Auto install formatter used by conform

lua/custom/plugins/conform.lua

@@ -1,20 +1,35 @@
 return {
   'stevearc/conform.nvim',
+  dependencies = {
+    'williamboman/mason.nvim',
+  },
   event = { 'BufReadPre', 'BufNewFile' },
   opts = {
     formatters_by_ft = {
       lua = { 'stylua' },
-      python = function(bufnr)
-        if require('conform').get_formatter_info('ruff_format', bufnr).available then
-          return { 'ruff_format' }
-        else
-          return { 'isort', 'black' }
-        end
-      end,
+      python = { 'ruff_format' },
     },
     format_on_save = {
       timeout_ms = 500,
       lsp_fallback = true,
     },
   },
+  config = function(_, opts)
+    local registry = require 'mason-registry'
+    registry.refresh(function()
+      for _, tbl in pairs(opts.formatters_by_ft) do
+        for _, pkg_name in ipairs(tbl) do
+          -- TODO the name formatters_by_ft needed may be different from the name mason needed
+          if pkg_name == 'ruff_format' then
+            pkg_name = 'ruff'
+          end
+          local pkg = registry.get_package(pkg_name)
+          if not pkg:is_installed() then
+            pkg:install()
+          end
+        end
+      end
+    end)
+    require('conform').setup(opts)
+  end,
 }