Add flag to set custom mypy cache directory (#1853)

Fixes #1414

This pull request adds the `--cache-dir` command line flag. Mypy will continue to
default to using `.mypy_cache` when the flag is omitted.

Usage:

    mypy --cache-dir ../.custom-cache my_module

Author: Michael0x2a

mypy/build.py

@@ -671,22 +671,21 @@ def read_with_python_encoding(path: str, pyversion: Tuple[int, int]) -> str:
         return source_bytearray.decode(encoding)
 
 
-MYPY_CACHE = '.mypy_cache'
-
-
-def get_cache_names(id: str, path: str, pyversion: Tuple[int, int]) -> Tuple[str, str]:
+def get_cache_names(id: str, path: str, cache_dir: str,
+                    pyversion: Tuple[int, int]) -> Tuple[str, str]:
     """Return the file names for the cache files.
 
     Args:
       id: module ID
       path: module path (used to recognize packages)
+      cache_dir: cache directory
       pyversion: Python version (major, minor)
 
     Returns:
       A tuple with the file names to be used for the meta JSON and the
       data JSON, respectively.
     """
-    prefix = os.path.join(MYPY_CACHE, '%d.%d' % pyversion, *id.split('.'))
+    prefix = os.path.join(cache_dir, '%d.%d' % pyversion, *id.split('.'))
     is_package = os.path.basename(path).startswith('__init__.py')
     if is_package:
         prefix = os.path.join(prefix, '__init__')
@@ -706,7 +705,8 @@ def find_cache_meta(id: str, path: str, manager: BuildManager) -> Optional[Cache
       valid; otherwise None.
     """
     # TODO: May need to take more build options into account
-    meta_json, data_json = get_cache_names(id, path, manager.options.python_version)
+    meta_json, data_json = get_cache_names(
+        id, path, manager.options.cache_dir, manager.options.python_version)
     manager.trace('Looking for {} {}'.format(id, data_json))
     if not os.path.exists(meta_json):
         return None
@@ -795,7 +795,8 @@ def write_cache(id: str, path: str, tree: MypyFile,
     st = os.stat(path)  # TODO: Errors
     mtime = st.st_mtime
     size = st.st_size
-    meta_json, data_json = get_cache_names(id, path, manager.options.python_version)
+    meta_json, data_json = get_cache_names(
+        id, path, manager.options.cache_dir, manager.options.python_version)
     manager.log('Writing {} {} {}'.format(id, meta_json, data_json))
     data = tree.serialize()
     parent = os.path.dirname(data_json)

mypy/defaults.py

@@ -1,2 +1,3 @@
 PYTHON2_VERSION = (2, 7)
 PYTHON3_VERSION = (3, 5)
+MYPY_CACHE = '.mypy_cache'

mypy/main.py

@@ -166,6 +166,9 @@ def parse_version(v: str) -> Tuple[int, int]:
                         help="enable experimental fast parser")
     parser.add_argument('-i', '--incremental', action='store_true',
                         help="enable experimental module cache")
+    parser.add_argument('--cache-dir', action='store', metavar='DIR',
+                        help="store module cache info in the given folder in incremental mode "
+                        "(defaults to '{}')".format(defaults.MYPY_CACHE))
     parser.add_argument('--strict-optional', action='store_true',
                         dest='special-opts:strict_optional',
                         help="enable experimental strict Optional checks")

mypy/options.py

@@ -55,6 +55,7 @@ def __init__(self) -> None:
         # -- experimental options --
         self.fast_parser = False
         self.incremental = False
+        self.cache_dir = defaults.MYPY_CACHE
 
     def __eq__(self, other: object) -> bool:
         return self.__class__ == other.__class__ and self.__dict__ == other.__dict__

mypy/test/testcheck.py

@@ -8,7 +8,7 @@
 
 from typing import Tuple, List, Dict, Set
 
-from mypy import build
+from mypy import build, defaults
 import mypy.myunit  # for mutable globals (ick!)
 from mypy.build import BuildSource, find_module_clear_caches
 from mypy.myunit import Suite, AssertionFailure
@@ -96,7 +96,7 @@ def run_test(self, testcase: DataDrivenTestCase) -> None:
             self.run_test_once(testcase)
 
     def clear_cache(self) -> None:
-        dn = build.MYPY_CACHE
+        dn = defaults.MYPY_CACHE
 
         if os.path.exists(dn):
             shutil.rmtree(dn)