Teach Mypy about sqlalchemy's declarative_base()

Mypy complains about alias for
sqlalchemy.ext.declarative.declarative_base() and everywhere where it is
used. SQLAlchemy has a stubs to tell Mypy about those which gets rid of
lots of Mypy warnings.

Reviewed By: PrzemekWirkus

Differential Revision: https://reviews.llvm.org/D94664

Author: Thomas Preud'homme

lnt/server/db/migrations/upgrade_0_to_1.py

@@ -4,11 +4,11 @@
 # versioning.
 
 import sqlalchemy
+from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy import Float, String, Integer, Column, ForeignKey, Binary, DateTime
 from sqlalchemy.orm import relation
-from sqlalchemy.ext.declarative import declarative_base
 
-Base = declarative_base()  # type: sqlalchemy.ext.declarative.api.DeclarativeMeta
+Base = declarative_base()
 
 ###
 # Core Schema

lnt/server/db/migrations/upgrade_12_to_13.py

@@ -1,8 +1,9 @@
 # Adds new table to store jsonschema previously used to construct testsuite.
 import sqlalchemy
+from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy import Column, String, Binary
 
-Base = sqlalchemy.ext.declarative.declarative_base()
+Base = declarative_base()
 
 
 class TestSuiteJSONSchema(Base):

mypy.ini

@@ -0,0 +1,2 @@
+[mypy]
+plugins = sqlmypy

tox.ini

@@ -29,6 +29,7 @@ basepython = python3
 skip_install = true
 deps =
     mypy
+    sqlalchemy-stubs
 commands =
     # No where close to passing yet, but nice to have.
     - mypy --junit-xml=junit-{envname}.xml --py2 --ignore-missing-imports lnt
@@ -52,4 +53,4 @@ deps =
     sphinx_bootstrap_theme
 
 commands =
-    make -C {toxinidir}/docs/ html
+    make -C {toxinidir}/docs/ html