Support expansion of all path configuration options

This commit modifies parsing of all configuration options dealing with
paths so that they may be able to expand user home directories and
environment variables as per the 'cache_dir' configuration.

Author: hetmankp

docs/source/config_file.rst

@@ -21,6 +21,10 @@ Most flags correspond closely to :ref:`command-line flags
 <command-line>` but there are some differences in flag names and some
 flags may take a different value based on the module being processed.
 
+Some flags support user home directory and environment variable expansion.
+To refer to the user home directory, use ``~`` at the beginning of the path.
+To expand environment variables use ``$VARNAME`` or ``${VARNAME}``.
+
 Config file format
 ******************
 
@@ -355,7 +359,8 @@ a list of import discovery options that may be used
 
 ``python_executable`` (string)
     Specifies the path to the Python executable to inspect to collect
-    a list of available :ref:`PEP 561 packages <installed-packages>`. Defaults to
+    a list of available :ref:`PEP 561 packages <installed-packages>`. User
+    home directory and environment variables will be expanded. Defaults to
     the executable used to run mypy.
 
 ``no_silence_site_packages`` (bool, default False)
@@ -366,13 +371,15 @@ a list of import discovery options that may be used
 ``mypy_path`` (string)
     Specifies the paths to use, after trying the paths from ``MYPYPATH`` environment
     variable.  Useful if you'd like to keep stubs in your repo, along with the config file.
+    Multiple paths are always separated with a ``:`` or ``,`` regardless of the platform.
+    User home directory and environment variables will be expanded.
 
 ``files`` (string)
     A comma-separated list of paths which should be checked by mypy if none are given on the command
     line. Supports recursive file globbing using
     [the glob library](https://docs.python.org/3/library/glob.html), where `*` (e.g. `*.py`) matches
     files in the current directory and `**/` (e.g. `**/*.py`) matches files in any directories below
-    the current one.
+    the current one. User home directory and environment variables will be expanded.
 
 
 Platform configuration
@@ -447,7 +454,8 @@ section of the command line docs.
 
 ``custom_typeshed_dir`` (string)
     Specifies an alternative directory to look for stubs instead of the
-    default ``typeshed`` directory.
+    default ``typeshed`` directory. User home directory and environment
+    variables will be expanded.
 
 ``warn_incomplete_stub`` (bool, default False)
     Warns about missing type annotations in typeshed.  This is only relevant

mypy/config_parser.py

@@ -46,6 +46,7 @@ def split_and_match_files(paths: str) -> List[str]:
 
     for path in paths.split(','):
         path = path.strip()
+        path = os.path.expandvars(os.path.expanduser(path))
         globbed_files = fileglob.glob(path, recursive=True)
         if globbed_files:
             expanded_paths.extend(globbed_files)
@@ -64,7 +65,8 @@ def split_and_match_files(paths: str) -> List[str]:
     'strict_optional_whitelist': lambda s: s.split(),
     'custom_typing_module': str,
     'custom_typeshed_dir': str,
-    'mypy_path': lambda s: [p.strip() for p in re.split('[,:]', s)],
+    'mypy_path': lambda s: [os.path.expandvars(os.path.expanduser(p.strip()))
+                            for p in re.split('[,:]', s)],
     'files': split_and_match_files,
     'quickstart_file': str,
     'junit_xml': str,
@@ -75,6 +77,9 @@ def split_and_match_files(paths: str) -> List[str]:
     'always_true': lambda s: [p.strip() for p in s.split(',')],
     'always_false': lambda s: [p.strip() for p in s.split(',')],
     'package_root': lambda s: [p.strip() for p in s.split(',')],
+    'cache_dir': lambda s: os.path.expandvars(os.path.expanduser(s)),
+    'custom_typeshed_dir': lambda s: os.path.expandvars(os.path.expanduser(s)),
+    'python_executable': lambda s: os.path.expandvars(os.path.expanduser(s)),
 }  # type: Final
 
 
@@ -223,8 +228,6 @@ def parse_section(prefix: str, template: Options,
         except ValueError as err:
             print("%s%s: %s" % (prefix, key, err), file=stderr)
             continue
-        if key == 'cache_dir':
-            v = os.path.expandvars(os.path.expanduser(v))
         if key == 'silent_imports':
             print("%ssilent_imports has been replaced by "
                   "ignore_missing_imports=True; follow_imports=skip" % prefix, file=stderr)