In bazel mode, always use "." as the cache prefix. (python#6122)

gvanrossum · web-flow · commit b0319aff582d · 2018-12-31T19:44:41.000-08:00
Without this, the files in the cache map aren't found,
and the build becomes O(N^2).
diff --git a/mypy/build.py b/mypy/build.py
@@ -802,6 +802,9 @@ def _load_json_file(file: str, manager: BuildManager,
 
 def _cache_dir_prefix(manager: BuildManager) -> str:
     """Get current cache directory (or file if id is given)."""
+    if manager.options.bazel:
+        # This is needed so the cache map works.
+        return os.curdir
     cache_dir = manager.options.cache_dir
     pyversion = manager.options.python_version
     base = os.path.join(cache_dir, '%d.%d' % pyversion)
