Add --migrate flag to mix format (#13846)

lib/elixir/src/elixir_bitstring.erl

@@ -403,10 +403,13 @@ format_error({undefined_bittype, Expr}) ->
  io_lib:format("unknown bitstring specifier: ~ts", ['Elixir.Macro':to_string(Expr)]);
 format_error({unknown_bittype, Name}) ->
  io_lib:format("bitstring specifier \"~ts\" does not exist and is being expanded to \"~ts()\","
- " please use parentheses to remove the ambiguity", [Name, Name]);
+ " please use parentheses to remove the ambiguity.\n"
+ "You may run \"mix format --migrate\" to fix this warning automatically.", [Name, Name]);
 format_error({parens_bittype, Name}) ->
  io_lib:format("extra parentheses on a bitstring specifier \"~ts()\" have been deprecated. "
- "Please remove the parentheses: \"~ts\"",
+ "Please remove the parentheses: \"~ts\".\n"
+ "You may run \"mix format --migrate\" to fix this warning automatically."
+ ,
  [Name, Name]);
 format_error({bittype_mismatch, Val1, Val2, Where}) ->
  io_lib:format("conflicting ~ts specification for bit field: \"~p\" and \"~p\"", [Where, Val1, Val2]);

lib/elixir/src/elixir_tokenizer.erl

@@ -267,7 +267,10 @@ tokenize([$" | T], Line, Column, Scope, Tokens) ->
 
 %% TODO: Remove me in Elixir v2.0
 tokenize([$' | T], Line, Column, Scope, Tokens) ->
- NewScope = prepend_warning(Line, Column, "single-quoted strings represent charlists. Use ~c\"\" if you indeed want a charlist or use \"\" instead", Scope),
+ Message = "single-quoted strings represent charlists. "
+ "Use ~c\"\" if you indeed want a charlist or use \"\" instead.\n"
+ "You may run \"mix format --migrate\" to fix this warning automatically.",
+ NewScope = prepend_warning(Line, Column, Message, Scope),
  handle_strings(T, Line, Column + 1, $', NewScope, Tokens);
 
 % Operator atoms

lib/mix/lib/mix/tasks/format.ex

@@ -78,6 +78,14 @@ defmodule Mix.Tasks.Format do
  as `.heex`. Without passing this flag, it is assumed that the code being
  passed via stdin is valid Elixir code. Defaults to "stdin.exs".
 
+ * `--migrate` - enables the `:migrate` option, which should be able to
+ automatically fix some deprecation warnings but is changing the AST.
+ This should be safe in typical projects, but there is a non-zero risk
+ of breaking code for meta-programming heavy projects that relied on a
+ specific AST, or projects that are re-defining functions from the `Kernel`.
+ See the "Migration formatting" section in `Code.format_string!/2` for
+ more information.
+
  ## When to format code
 
  We recommend developers to format code directly in their editors, either
@@ -184,7 +192,8 @@ defmodule Mix.Tasks.Format do
  dot_formatter: :string,
  dry_run: :boolean,
  stdin_filename: :string,
- force: :boolean
+ force: :boolean,
+ migrate: :boolean
  ]
 
  @manifest_timestamp "format_timestamp"
@@ -362,17 +371,21 @@ defmodule Mix.Tasks.Format do
  end
 
  defp eval_dot_formatter(cwd, opts) do
- cond do
- dot_formatter = opts[:dot_formatter] ->
- {dot_formatter, eval_file_with_keyword_list(dot_formatter)}
+ {dot_formatter, format_opts} =
+ cond do
+ dot_formatter = opts[:dot_formatter] ->
+ {dot_formatter, eval_file_with_keyword_list(dot_formatter)}
 
- File.regular?(Path.join(cwd, ".formatter.exs")) ->
- dot_formatter = Path.join(cwd, ".formatter.exs")
- {".formatter.exs", eval_file_with_keyword_list(dot_formatter)}
+  File.regular?(Path.join(cwd, ".formatter.exs")) ->
+  dot_formatter = Path.join(cwd, ".formatter.exs")
+  {".formatter.exs", eval_file_with_keyword_list(dot_formatter)}
 
- true ->
- {".formatter.exs", []}
- end
+ true ->
+ {".formatter.exs", []}
+ end
+
+ # the --migrate flag overrides settings from the dot formatter
+ {dot_formatter, Keyword.take(opts, [:migrate]) ++ format_opts}
  end
 
  # This function reads exported configuration from the imported

lib/mix/test/mix/tasks/format_test.exs

@@ -534,6 +534,18 @@ defmodule Mix.Tasks.FormatTest do
  end)
  end
 
+ test "respects the --migrate flag", context do
+ in_tmp(context.test, fn ->
+ File.write!("a.ex", "unless foo, do: 'bar'\n")
+
+ Mix.Tasks.Format.run(["a.ex"])
+ assert File.read!("a.ex") == "unless foo, do: 'bar'\n"
+
+ Mix.Tasks.Format.run(["a.ex", "--migrate"])
+ assert File.read!("a.ex") == "if !foo, do: ~c\"bar\"\n"
+ end)
+ end
+
  test "uses inputs and configuration from --dot-formatter", context do
  in_tmp(context.test, fn ->
  File.write!("custom_formatter.exs", """