Use a more intelligent default language version

pre_commit/languages/all.py

@@ -10,16 +10,18 @@ from pre_commit.languages import script
 from pre_commit.languages import swift
 from pre_commit.languages import system
 
-# A language implements the following constant and two functions in its module:
+# A language implements the following constant and functions in its module:
 #
 # # Use None for no environment
 # ENVIRONMENT_DIR = 'foo_env'
 #
-# def install_environment(
-#         repo_cmd_runner,
-#         version='default',
-#         additional_dependencies=(),
-# ):
+# def get_default_version():
+#     """Return a value to replace the 'default' value for language_version.
+#
+#     return 'default' if there is no better option.
+#    """
+#
+# def install_environment(repo_cmd_runner, version, additional_dependencies):
 #     """Installs a repository in the given repository.  Note that the current
 #     working directory will already be inside the repository.
 #

pre_commit/languages/docker.py

@@ -14,6 +14,7 @@ from pre_commit.xargs import xargs
 
 ENVIRONMENT_DIR = 'docker'
 PRE_COMMIT_LABEL = 'PRE_COMMIT'
+get_default_version = helpers.basic_get_default_version
 
 
 def md5(s):  # pragma: windows no cover
@@ -55,9 +56,7 @@ def build_docker_image(repo_cmd_runner, **kwargs):  # pragma: windows no cover
 
 
 def install_environment(
-        repo_cmd_runner,
-        version='default',
-        additional_dependencies=(),
+        repo_cmd_runner, version, additional_dependencies,
 ):  # pragma: windows no cover
     assert repo_cmd_runner.exists('Dockerfile'), (
         'No Dockerfile was found in the hook repository'

pre_commit/languages/golang.py

@@ -14,6 +14,7 @@ from pre_commit.xargs import xargs
 
 
 ENVIRONMENT_DIR = 'golangenv'
+get_default_version = helpers.basic_get_default_version
 
 
 def get_env_patch(venv):
@@ -44,11 +45,7 @@ def guess_go_dir(remote_url):
         return 'unknown_src_dir'
 
 
-def install_environment(
-        repo_cmd_runner,
-        version='default',
-        additional_dependencies=(),
-):
+def install_environment(repo_cmd_runner, version, additional_dependencies):
     helpers.assert_version_default('golang', version)
     directory = repo_cmd_runner.path(
         helpers.environment_dir(ENVIRONMENT_DIR, 'default'),

pre_commit/languages/helpers.py

@@ -33,3 +33,7 @@ def assert_no_additional_deps(lang, additional_deps):
             'For now, pre-commit does not support '
             'additional_dependencies for {}'.format(lang),
         )
+
+
+def basic_get_default_version():
+    return 'default'

pre_commit/languages/node.py

@@ -12,6 +12,7 @@ from pre_commit.xargs import xargs
 
 
 ENVIRONMENT_DIR = 'node_env'
+get_default_version = helpers.basic_get_default_version
 
 
 def get_env_patch(venv):  # pragma: windows no cover
@@ -34,9 +35,7 @@ def in_env(repo_cmd_runner, language_version):  # pragma: windows no cover
 
 
 def install_environment(
-        repo_cmd_runner,
-        version='default',
-        additional_dependencies=(),
+        repo_cmd_runner, version, additional_dependencies,
 ):  # pragma: windows no cover
     additional_dependencies = tuple(additional_dependencies)
     assert repo_cmd_runner.exists('package.json')

pre_commit/languages/pcre.py

@@ -2,18 +2,16 @@ from __future__ import unicode_literals
 
 import sys
 
+from pre_commit.languages import helpers
 from pre_commit.xargs import xargs
 
 
 ENVIRONMENT_DIR = None
 GREP = 'ggrep' if sys.platform == 'darwin' else 'grep'
+get_default_version = helpers.basic_get_default_version
 
 
-def install_environment(
-        repo_cmd_runner,
-        version='default',
-        additional_dependencies=(),
-):
+def install_environment(repo_cmd_runner, version, additional_dependencies):
     """Installation for pcre type is a noop."""
     raise AssertionError('Cannot install pcre repo.')
 

pre_commit/languages/python.py

@@ -1,7 +1,6 @@
 from __future__ import unicode_literals
 
 import contextlib
-import distutils.spawn
 import os
 import sys
 
@@ -9,11 +8,13 @@ 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.parse_shebang import find_executable
 from pre_commit.util import clean_path_on_failure
 from pre_commit.xargs import xargs
 
 
 ENVIRONMENT_DIR = 'py_env'
+get_default_version = helpers.basic_get_default_version
 
 
 def bin_dir(venv):
@@ -39,10 +40,53 @@ def in_env(repo_cmd_runner, language_version):
         yield
 
 
+def _get_default_version():  # pragma: no cover (platform dependent)
+    def _norm(path):
+        _, exe = os.path.split(path.lower())
+        exe, _, _ = exe.partition('.exe')
+        if find_executable(exe) and exe not in {'python', 'pythonw'}:
+            return exe
+
+    # First attempt from `sys.executable` (or the realpath)
+    # On linux, I see these common sys.executables:
+    #
+    # system `python`: /usr/bin/python -> python2.7
+    # system `python2`: /usr/bin/python2 -> python2.7
+    # virtualenv v: v/bin/python (will not return from this loop)
+    # virtualenv v -ppython2: v/bin/python -> python2
+    # virtualenv v -ppython2.7: v/bin/python -> python2.7
+    # virtualenv v -ppypy: v/bin/python -> v/bin/pypy
+    for path in {sys.executable, os.path.realpath(sys.executable)}:
+        exe = _norm(path)
+        if exe:
+            return exe
+
+    # Next try the `pythonX.X` executable
+    exe = 'python{}.{}'.format(*sys.version_info)
+    if find_executable(exe):
+        return exe
+
+    # Give a best-effort try for windows
+    if os.path.exists(r'C:\{}\python.exe'.format(exe.replace('.', ''))):
+        return exe
+
+    # We tried!
+    return 'default'
+
+
+def get_default_version():
+    # TODO: when dropping python2, use `functools.lru_cache(maxsize=1)`
+    try:
+        return get_default_version.cached_version
+    except AttributeError:
+        get_default_version.cached_version = _get_default_version()
+        return get_default_version()
+
+
 def norm_version(version):
     if os.name == 'nt':  # pragma: no cover (windows)
         # Try looking up by name
-        if distutils.spawn.find_executable(version):
+        if find_executable(version) and find_executable(version) != version:
             return version
 
         # If it is in the form pythonx.x search in the default
@@ -54,11 +98,7 @@ def norm_version(version):
     return os.path.expanduser(version)
 
 
-def install_environment(
-        repo_cmd_runner,
-        version='default',
-        additional_dependencies=(),
-):
+def install_environment(repo_cmd_runner, version, additional_dependencies):
     additional_dependencies = tuple(additional_dependencies)
     directory = helpers.environment_dir(ENVIRONMENT_DIR, version)
 

pre_commit/languages/ruby.py

@@ -16,6 +16,7 @@ from pre_commit.xargs import xargs
 
 
 ENVIRONMENT_DIR = 'rbenv'
+get_default_version = helpers.basic_get_default_version
 
 
 def get_env_patch(venv, language_version):  # pragma: windows no cover
@@ -97,9 +98,7 @@ def _install_ruby(runner, version):  # pragma: windows no cover
 
 
 def install_environment(
-        repo_cmd_runner,
-        version='default',
-        additional_dependencies=(),
+        repo_cmd_runner, version, additional_dependencies,
 ):  # pragma: windows no cover
     additional_dependencies = tuple(additional_dependencies)
     directory = helpers.environment_dir(ENVIRONMENT_DIR, version)

pre_commit/languages/script.py

@@ -5,13 +5,10 @@ from pre_commit.xargs import xargs
 
 
 ENVIRONMENT_DIR = None
+get_default_version = helpers.basic_get_default_version
 
 
-def install_environment(
-        repo_cmd_runner,
-        version='default',
-        additional_dependencies=(),
-):
+def install_environment(repo_cmd_runner, version, additional_dependencies):
     """Installation for script type is a noop."""
     raise AssertionError('Cannot install script repo.')
 

pre_commit/languages/swift.py

@@ -10,6 +10,7 @@ from pre_commit.util import clean_path_on_failure
 from pre_commit.xargs import xargs
 
 ENVIRONMENT_DIR = 'swift_env'
+get_default_version = helpers.basic_get_default_version
 BUILD_DIR = '.build'
 BUILD_CONFIG = 'release'
 
@@ -29,9 +30,7 @@ def in_env(repo_cmd_runner):  # pragma: windows no cover
 
 
 def install_environment(
-        repo_cmd_runner,
-        version='default',
-        additional_dependencies=(),
+        repo_cmd_runner, version, additional_dependencies,
 ):  # pragma: windows no cover
     helpers.assert_version_default('swift', version)
     helpers.assert_no_additional_deps('swift', additional_dependencies)

pre_commit/languages/system.py

@@ -5,13 +5,10 @@ from pre_commit.xargs import xargs
 
 
 ENVIRONMENT_DIR = None
+get_default_version = helpers.basic_get_default_version
 
 
-def install_environment(
-        repo_cmd_runner,
-        version='default',
-        additional_dependencies=(),
-):
+def install_environment(repo_cmd_runner, version, additional_dependencies):
     """Installation for system type is a noop."""
     raise AssertionError('Cannot install system repo.')