give docker a tty output when expecting color

this makes the behavior more consistent with the system language
and would help the executable run in a docker container to
produce a colored output.

pre_commit/languages/docker.py

@@ -108,10 +108,15 @@ def get_docker_user() -> tuple[str, ...]:  # pragma: win32 no cover
         return ()
 
 
-def docker_cmd() -> tuple[str, ...]:  # pragma: win32 no cover
+def get_docker_tty(*, color: bool) -> tuple[str, ...]:  # pragma: win32 no cover  # noqa: E501
+    return (('--tty',) if color else ())
+
+
+def docker_cmd(*, color: bool) -> tuple[str, ...]:  # pragma: win32 no cover
     return (
         'docker', 'run',
         '--rm',
+        *get_docker_tty(color=color),
         *get_docker_user(),
         # https://docs.docker.com/engine/reference/commandline/run/#mount-volumes-from-container-volumes-from
         # The `Z` option tells Docker to label the content with a private
@@ -139,7 +144,7 @@ def run_hook(
 
     entry_tag = ('--entrypoint', entry_exe, docker_tag(prefix))
     return lang_base.run_xargs(
-        (*docker_cmd(), *entry_tag, *cmd_rest),
+        (*docker_cmd(color=color), *entry_tag, *cmd_rest),
         file_args,
         require_serial=require_serial,
         color=color,

pre_commit/languages/docker_image.py

@@ -23,7 +23,7 @@ def run_hook(
         require_serial: bool,
         color: bool,
 ) -> tuple[int, bytes]:  # pragma: win32 no cover
-    cmd = docker_cmd() + lang_base.hook_cmd(entry, args)
+    cmd = docker_cmd(color=color) + lang_base.hook_cmd(entry, args)
     return lang_base.run_xargs(
         cmd,
         file_args,

tests/languages/docker_image_test.py

@@ -25,3 +25,27 @@ def test_docker_image_hook_via_args(tmp_path):
         args=('hello hello world',),
     )
     assert ret == (0, b'hello hello world\n')
+
+
+@xfailif_windows  # pragma: win32 no cover
+def test_docker_image_color_tty(tmp_path):
+    ret = run_language(
+        tmp_path,
+        docker_image,
+        'ubuntu:22.04',
+        args=('grep', '--color', 'root', '/etc/group'),
+        color=True,
+    )
+    assert ret == (0, b'\x1b[01;31m\x1b[Kroot\x1b[m\x1b[K:x:0:\n')
+
+
+@xfailif_windows  # pragma: win32 no cover
+def test_docker_image_no_color_no_tty(tmp_path):
+    ret = run_language(
+        tmp_path,
+        docker_image,
+        'ubuntu:22.04',
+        args=('grep', '--color', 'root', '/etc/group'),
+        color=False,
+    )
+    assert ret == (0, b'root:x:0:\n')