[CI] Use the latest LibCST source code in Pyre check

.circleci/.pyre_configuration

@@ -0,0 +1,11 @@
+{
+    "source_directories": [
+        "."
+    ],
+    "search_path": [
+        "stubs", "/tmp/libcst-env/lib/python3.7/site-packages"
+    ],
+    "exclude": [
+        ".*/\\.tox/.*"
+    ]
+}

.circleci/config.yml

@@ -71,7 +71,10 @@ jobs:
             source /tmp/libcst-env/bin/activate
             pip install --upgrade pip
             pip install -r requirements.txt -r requirements-dev.txt
-            pyre --preserve-pythonpath check
+            pip uninstall -y libcst
+            pip install -e .
+            cp .circleci/.pyre_configuration .
+            pyre check
             PYTHONPATH=`pwd` python libcst/tests/test_pyre_integration.py
             git diff --exit-code  # verify no generated changes
       - save_cache:

.gitignore

@@ -12,3 +12,4 @@ docs/source/.ipynb_checkpoints/
 build/
 .coverage
 .hypothesis/
+.pyre_configuration

README.rst

@@ -176,12 +176,23 @@ this:
 See the `unittest documentation <https://docs.python.org/3/library/unittest.html>`_
 for more examples of how to run tests.
 
-We use `Pyre <https://github.com/facebook/pyre-check>`_ for type-checking. To
-verify types for the library, do the following in the root:
+We use `Pyre <https://github.com/facebook/pyre-check>`_ for type-checking.
+
+To set up pyre check environment:
+
+1. Copy the example Pyre config: ``cp .pyre_configuration.example .pyre_configuration``.
+2. In the config file, add your venv site-pacakges dir to "search_path". (e.g. add "/workspace/libcst-env/lib/python3.7/site-packages")
+2. Remove installed LibCST and install from the source code:
+
+.. code-block:: shell
+    pip uninstall -y libcst
+    pip install -e .
+
+To verify types for the library, do the following in the root:
 
 .. code-block:: shell
 
-    pyre --preserve-pythonpath check
+    pyre check
 
 To generate documents, do the following in the root: