requirements: Upgrade to mypy 0.720.

We also add the option of the newly added `--warn_unreachable`
flag.

requirements/dev.txt

@@ -90,7 +90,7 @@ matrix-client==0.3.2
 mock==2.0.0
 moto==1.3.7
 mypy-extensions==0.4.1
-mypy==0.711
+mypy==0.720
 oauthlib==3.0.1           # via requests-oauthlib, social-auth-core
 packaging==19.0           # via sphinx
 parsel==1.5.1             # via scrapy
@@ -171,6 +171,7 @@ transifex-client==0.12.5
 twilio==6.26.2
 twisted==19.2.1
 typed-ast==1.4.0          # via mypy
+typing-extensions==3.7.4  # via mypy
 typing==3.6.6
 urllib3==1.25.3           # via botocore, requests, transifex-client
 virtualenv-clone==0.5.3

requirements/mypy.in

@@ -2,4 +2,4 @@
 # /tools/update-locked-requirements to update requirements/dev.txt
 # and requirements/mypy.txt.
 # See requirements/README.md for more detail.
-mypy==0.711
+mypy==0.720

requirements/mypy.txt

@@ -8,5 +8,6 @@
 # For details, see requirements/README.md .
 #
 mypy-extensions==0.4.1    # via mypy
-mypy==0.711
+mypy==0.720
 typed-ast==1.4.0          # via mypy
+typing-extensions==3.7.4  # via mypy

tools/run-mypy

@@ -36,6 +36,8 @@ parser.add_argument('-a', '--all', action='store_true',
                     help="check all files, bypassing the default exclude list")
 parser.add_argument('--force', action="store_true",
                     help="run tests despite possible provisioning problems")
+parser.add_argument('--warn-unreachable', action='store_true',
+                    help="warn of unreachable or redundant code.")
 args = parser.parse_args()
 
 assert_provisioning_status_ok(args.force)
@@ -73,6 +75,8 @@ if not python_files and not pyi_files:
 extra_args = []
 if args.quick:
     extra_args.append("--quick")
+elif args.warn_unreachable:
+    extra_args.append("--warn-unreachable")
 
 mypy_args = extra_args + python_files + pyi_files
 if args.no_daemon: