Warn for missing returns with explicit Any return types

[hauntsaninja]

As discussed in #7511, mypy's --warn-no-return isn't really a question of type safety. It does however enforce a PEP 8 rule that is "dear to Guido's heart", and I think we should enforce it for functions that explicitly return Any as well.

Fixes #16095

[hauntsaninja]

Hmm, more hits than I was hoping for. Most of them are PEP 8 violations, the few that are not should straightforwardly be -> None. Still, might eat more into our disruption budget than we want.

[sobolevn]

Let's also test correct cases to be correct.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

porcupine (https://github.com/Akuli/porcupine)
+ porcupine/_state.py:41: error: Missing return statement  [return]

pylox (https://github.com/sco1/pylox)
+ pylox/callable.py:41: error: Missing return statement  [return]

comtypes (https://github.com/enthought/comtypes)
+ comtypes/tools/tlbparser.py:583: error: Missing return statement  [return]

jinja (https://github.com/pallets/jinja)
+ src/jinja2/utils.py:131: error: Missing return statement  [return]
+ src/jinja2/visitor.py:44: error: Missing return statement  [return]

zetta_utils (https://github.com/ZettaAI/zetta_utils)
+ zetta_utils/builder/build.py:100: error: Missing return statement  [return]

prefect (https://github.com/PrefectHQ/prefect)
+ src/prefect/utilities/visualization.py:51: error: Missing return statement  [return]

sphinx (https://github.com/sphinx-doc/sphinx)
+ sphinx/util/display.py: note: In function "__call__":
+ sphinx/util/display.py:90:9: error: Missing return statement  [return]
+ sphinx/testing/fixtures.py: note: In member "store" of class "SharedResult":
+ sphinx/testing/fixtures.py:43:5: error: Missing return statement  [return]

graphql-core (https://github.com/graphql-python/graphql-core)
+ src/graphql/utilities/type_info.py:276: error: Missing return statement  [return]
+ src/graphql/execution/execute.py:1805: error: Missing return statement  [return]

vision (https://github.com/pytorch/vision)
+ torchvision/transforms/v2/_misc.py:106: error: Missing return statement  [return]
+ torchvision/transforms/v2/_misc.py:166: error: Missing return statement  [return]

sublime_debugger (https://github.com/daveleroy/sublime_debugger)
+ modules/core/sublime.py:71: error: Missing return statement  [return]
+ modules/output_panel.py:328: error: Missing return statement  [return]
+ modules/adapters/js.py:64: error: Missing return statement  [return]

bandersnatch (https://github.com/pypa/bandersnatch)
+ src/bandersnatch/master.py: note: In member "rpc" of class "Master":
+ src/bandersnatch/master.py:191: error: Missing return statement  [return]

spark (https://github.com/apache/spark)
+ python/pyspark/sql/types.py:1161: error: Missing return statement  [return]
+ python/pyspark/sql/types.py:1165: error: Missing return statement  [return]
+ python/pyspark/ml/torch/data.py:38: error: Missing return statement  [return]
+ python/pyspark/sql/connect/client/reattach.py:299: error: Missing return statement  [return]
+ python/pyspark/pandas/frame.py:13243: error: Missing return statement  [return]
+ python/pyspark/pandas/resample.py:736: error: Missing return statement  [return]
+ python/pyspark/pandas/resample.py:768: error: Missing return statement  [return]

schemathesis (https://github.com/schemathesis/schemathesis)
+ src/schemathesis/parameters.py: note: In member "example" of class "PayloadAlternatives":
+ src/schemathesis/parameters.py:92: error: Missing return statement  [return]
+ src/schemathesis/specs/openapi/parameters.py: note: In member "example" of class "OpenAPIParameter":
+ src/schemathesis/specs/openapi/parameters.py:26: error: Missing return statement  [return]

ignite (https://github.com/pytorch/ignite)
+ ignite/engine/engine.py:252: error: Missing return statement  [return]
+ ignite/distributed/auto.py:354: error: Missing return statement  [return]
+ ignite/contrib/handlers/neptune_logger.py:163: error: Missing return statement  [return]

pandera (https://github.com/pandera-dev/pandera)
+ pandera/decorators.py:613: error: Missing return statement  [return]

mongo-python-driver (https://github.com/mongodb/mongo-python-driver)
+ gridfs/grid_file.py: note: In function "_grid_in_property":
+ gridfs/grid_file.py:73: error: Missing return statement  [return]

pydantic (https://github.com/samuelcolvin/pydantic)
+ pydantic/main.py:782: error: Missing return statement  [return]

aiohttp (https://github.com/aio-libs/aiohttp)
+ aiohttp/test_utils.py:611:5: error: Missing return statement  [return]
+ aiohttp/test_utils.py:611:5: note: See https://mypy.rtfd.io/en/stable/_refs.html#code-return for more info

streamlit (https://github.com/streamlit/streamlit)
+ lib/tests/streamlit/external/langchain/capturing_callback_handler.py: note: In member "on_agent_action" of class "CapturingCallbackHandler":
+ lib/tests/streamlit/external/langchain/capturing_callback_handler.py:196:5: error: Missing return statement  [return]
+ lib/streamlit/external/langchain/streamlit_callback_handler.py: note: In member "on_agent_action" of class "StreamlitCallbackHandler":
+ lib/streamlit/external/langchain/streamlit_callback_handler.py:383:5: error: Missing return statement  [return]

scrapy (https://github.com/scrapy/scrapy)
+ scrapy/utils/trackref.py:58: error: Missing return statement  [return]

discord.py (https://github.com/Rapptz/discord.py)
+ discord/ext/commands/context.py:544: error: Missing return statement  [return]
+ discord/ext/commands/cooldowns.py:64: error: Missing return statement  [return]
+ discord/ext/commands/hybrid.py:133: error: Missing return statement  [return]

urllib3 (https://github.com/urllib3/urllib3)
+ test/test_wait.py:111: error: Missing return statement  [return]
+ test/test_wait.py:142: error: Missing return statement  [return]
+ test/test_wait.py:176: error: Missing return statement  [return]

[jakethesnake420]

bump this

[hauntsaninja]

I think this is too disruptive for too little benefit