Support for conda as a language

pre_commit/languages/all.py

@@ -1,5 +1,6 @@
 from __future__ import unicode_literals
 
+from pre_commit.languages import conda
 from pre_commit.languages import docker
 from pre_commit.languages import docker_image
 from pre_commit.languages import fail
@@ -52,6 +53,7 @@ from pre_commit.languages import system
 #     """
 
 languages = {
+    'conda': conda,
     'docker': docker,
     'docker_image': docker_image,
     'fail': fail,

pre_commit/languages/conda.py

@@ -0,0 +1,66 @@
+import contextlib
+import os
+
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import UNSET
+from pre_commit.envcontext import Var
+from pre_commit.languages import helpers
+from pre_commit.util import clean_path_on_failure
+from pre_commit.util import cmd_output_b
+
+ENVIRONMENT_DIR = 'conda'
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+
+
+def get_env_patch(env):
+    # On non-windows systems executable live in $CONDA_PREFIX/bin, on Windows
+    # they can be in $CONDA_PREFIX/bin, $CONDA_PREFIX/Library/bin,
+    # $CONDA_PREFIX/Scripts and $CONDA_PREFIX. Whereas the latter only
+    # seems to be used for python.exe.
+    path = (os.path.join(env, 'bin'), os.pathsep, Var('PATH'))
+    if os.name == 'nt':  # pragma: no cover (platform specific)
+        path = (env, os.pathsep) + path
+        path = (os.path.join(env, 'Scripts'), os.pathsep) + path
+        path = (os.path.join(env, 'Library', 'bin'), os.pathsep) + path
+
+    return (
+        ('PYTHONHOME', UNSET),
+        ('VIRTUAL_ENV', UNSET),
+        ('CONDA_PREFIX', env),
+        ('PATH', path),
+    )
+
+
+@contextlib.contextmanager
+def in_env(prefix, language_version):
+    directory = helpers.environment_dir(ENVIRONMENT_DIR, language_version)
+    envdir = prefix.path(directory)
+    with envcontext(get_env_patch(envdir)):
+        yield
+
+
+def install_environment(prefix, version, additional_dependencies):
+    helpers.assert_version_default('conda', version)
+    directory = helpers.environment_dir(ENVIRONMENT_DIR, version)
+
+    env_dir = prefix.path(directory)
+    with clean_path_on_failure(env_dir):
+        cmd_output_b(
+            'conda', 'env', 'create', '-p', env_dir, '--file',
+            'environment.yml', cwd=prefix.prefix_dir,
+        )
+        if additional_dependencies:
+            cmd_output_b(
+                'conda', 'install', '-p', env_dir, *additional_dependencies,
+                cwd=prefix.prefix_dir
+            )
+
+
+def run_hook(hook, file_args, color):
+    # TODO: Some rare commands need to be run using `conda run` but mostly we
+    #       can run them withot which is much quicker and produces a better
+    #       output.
+    # cmd = ('conda', 'run', '-p', env_dir) + hook.cmd
+    with in_env(hook.prefix, hook.language_version):
+        return helpers.run_xargs(hook, hook.cmd, file_args, color=color)