Add --no-compile to mix format

Closes #15256.

Author: josevalim

lib/elixir/lib/option_parser.ex

@@ -952,8 +952,14 @@ defmodule OptionParser do
 
         case types |> List.delete(:keep) |> List.first(:string) do
           :boolean ->
-            base = "#{to_switch(name)}, #{to_switch(name, "--no-")}"
-            add_aliases(base, name, reverse_aliases)
+            case to_switch(name) do
+              "--no-" <> _ = switch ->
+                add_aliases(switch, name, reverse_aliases)
+
+              switch ->
+                base = "#{switch}, #{to_switch(name, "--no-")}"
+                add_aliases(base, name, reverse_aliases)
+            end
 
           type ->
             base = "#{to_switch(name)} #{String.upcase(Atom.to_string(type))}"

lib/elixir/test/elixir/option_parser_test.exs

@@ -173,6 +173,7 @@ defmodule OptionParserTest do
         --debug, --no-debug (alias: -d)
         --files STRING (alias: -f) (may be given more than once)
         --name STRING (alias: -n)
+        --no-exit
         --verbose, --no-verbose (alias: -v)\
       """
 
@@ -183,7 +184,8 @@ defmodule OptionParserTest do
           count: :integer,
           verbose: :boolean,
           debug: :boolean,
-          files: :keep
+          files: :keep,
+          no_exit: :boolean
         ],
         aliases: [n: :name, c: :count, v: :verbose, d: :debug, f: :files]
       )

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

@@ -13,7 +13,8 @@ defmodule Mix.Tasks.Format do
       $ mix format mix.exs "lib/**/*.{ex,exs}" "test/**/*.{ex,exs}"
 
   If any of the files is `-`, then the input is read from stdin and the output
-  is written to stdout.
+  is written to stdout. In such cases, because `mix format` may still compile
+  before running, you may want to pass the `--no-compile` flag.
 
   ## Formatting options
 
@@ -199,6 +200,7 @@ defmodule Mix.Tasks.Format do
     check_equivalent: :boolean,
     check_formatted: :boolean,
     no_exit: :boolean,
+    no_compile: :boolean,
     dot_formatter: :string,
     dry_run: :boolean,
     verbose: :boolean,