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gh-104504: cases generator: Add --warn-unreachable to the mypy config #108112

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Merged
merged 9 commits into from
Aug 20, 2023
Merged

gh-104504: cases generator: Add --warn-unreachable to the mypy config #108112

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833586f
Improve the GitHub issue forms
AlexWaygood Aug 17, 2023
c0a42bc
Merge branch 'main' of https://github.com/python/cpython
AlexWaygood Aug 18, 2023
ba097e0
cases generator: Add `--warn-unreachable` to the mypy config
AlexWaygood Aug 18, 2023
e4a9e06
Actually assign it
AlexWaygood Aug 18, 2023
82bc6f6
Merge branch 'main' of https://github.com/python/cpython
AlexWaygood Aug 20, 2023
a27ffa0
Merge branch 'main' into cases-generator-reachability
AlexWaygood Aug 20, 2023
2f5206d
Fix one of the two locations
AlexWaygood Aug 20, 2023
ec78f7c
Fix the other one
AlexWaygood Aug 20, 2023
8497a68
Revert unrelated changes
AlexWaygood Aug 20, 2023
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15 changes: 15 additions & 0 deletions Tools/cases_generator/_typing_backports.py
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Original file line number Diff line number Diff line change
@@ -0,0 +1,15 @@
"""Backports from newer versions of the typing module.

We backport these features here so that Python can still build
while using an older Python version for PYTHON_FOR_REGEN.
"""

from typing import NoReturn


def assert_never(obj: NoReturn) -> NoReturn:
"""Statically assert that a line of code is unreachable.

Backport of typing.assert_never (introduced in Python 3.11).
"""
raise AssertionError(f"Expected code to be unreachable, but got: {obj}")
7 changes: 4 additions & 3 deletions Tools/cases_generator/analysis.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
import sys
import typing

from _typing_backports import assert_never
from flags import InstructionFlags, variable_used
from formatting import prettify_filename, UNUSED
from instructions import (
Expand Down Expand Up @@ -172,7 +173,7 @@ def parse_file(self, filename: str, instrs_idx: dict[str, int]) -> None:
self.pseudos[name] = thing
self.everything.append(thing)
case _:
typing.assert_never(thing)
assert_never(thing)
if not psr.eof():
raise psr.make_syntax_error(f"Extra stuff at the end of {filename}")

Expand Down Expand Up @@ -368,7 +369,7 @@ def analyze_macro(self, macro: parsing.Macro) -> MacroInstruction:
# SAVE_IP in a macro is a no-op in Tier 1
flags.add(instr.instr_flags)
case _:
typing.assert_never(component)
assert_never(component)
format = "IB" if flags.HAS_ARG_FLAG else "IX"
if offset:
format += "C" + "0" * (offset - 1)
Expand Down Expand Up @@ -409,5 +410,5 @@ def check_macro_components(
case parsing.CacheEffect():
components.append(uop)
case _:
typing.assert_never(uop)
assert_never(uop)
return components
33 changes: 13 additions & 20 deletions Tools/cases_generator/generate_cases.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
from collections.abc import Iterator

import stacking # Early import to avoid circular import
from _typing_backports import assert_never
from analysis import Analyzer
from formatting import Formatter, list_effect_size
from flags import InstructionFlags, variable_used
Expand Down Expand Up @@ -146,16 +147,14 @@
class Generator(Analyzer):
def get_stack_effect_info(
self, thing: parsing.InstDef | parsing.Macro | parsing.Pseudo
) -> tuple[AnyInstruction | None, str | None, str | None]:
) -> tuple[AnyInstruction | None, str, str]:
def effect_str(effects: list[StackEffect]) -> str:
n_effect, sym_effect = list_effect_size(effects)
if sym_effect:
return f"{sym_effect} + {n_effect}" if n_effect else sym_effect
return str(n_effect)

instr: AnyInstruction | None
popped: str | None
pushed: str | None
match thing:
case parsing.InstDef():
if thing.kind != "op" or self.instrs[thing.name].is_viable_uop():
Expand All @@ -171,25 +170,23 @@ def effect_str(effects: list[StackEffect]) -> str:
popped, pushed = stacking.get_stack_effect_info_for_macro(instr)
case parsing.Pseudo():
instr = self.pseudo_instrs[thing.name]
popped = pushed = None
# Calculate stack effect, and check that it's the the same
# for all targets.
for target in self.pseudos[thing.name].targets:
for idx, target in enumerate(self.pseudos[thing.name].targets):
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Clever idea. I wrote a whole paragraph arguing against using enumerate() here, then realized it wasn't worth arguing over. :-)

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FYI, the saga continues. Currently we get errors from pyright on this: "popped is possibly unbound" (on all occurrences of popped and pushed in this function below here).

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FYI, the saga continues. Currently we get errors from pyright on this: "popped is possibly unbound" (on all occurrences of popped and pushed in this function below here).

Yeah, and mypy will also give you that error if you add --enable-error-code=possibly-undefined to the mypy config :/

There is a third way of fixing this. I'll make a PR and see how you like it.

target_instr = self.instrs.get(target)
# Currently target is always an instr. This could change
# in the future, e.g., if we have a pseudo targetting a
# macro instruction.
assert target_instr
target_popped = effect_str(target_instr.input_effects)
target_pushed = effect_str(target_instr.output_effects)
if pushed is None:
assert popped is None
if idx == 0:
popped, pushed = target_popped, target_pushed
else:
assert popped == target_popped
assert pushed == target_pushed
case _:
typing.assert_never(thing)
assert_never(thing)
return instr, popped, pushed

@contextlib.contextmanager
Expand All @@ -209,7 +206,6 @@ def write_stack_effect_functions(self) -> None:
continue
instr, popped, pushed = self.get_stack_effect_info(thing)
if instr is not None:
assert popped is not None and pushed is not None
popped_data.append((instr, popped))
pushed_data.append((instr, pushed))

Expand Down Expand Up @@ -379,7 +375,6 @@ def write_metadata(self, metadata_filename: str, pymetadata_filename: str) -> No
# Compute the set of all instruction formats.
all_formats: set[str] = set()
for thing in self.everything:
format: str | None
match thing:
case OverriddenInstructionPlaceHolder():
continue
Expand All @@ -388,17 +383,15 @@ def write_metadata(self, metadata_filename: str, pymetadata_filename: str) -> No
case parsing.Macro():
format = self.macro_instrs[thing.name].instr_fmt
case parsing.Pseudo():
format = None
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Similarly, here mypy was eagerly narrowing the type of format to None, meaning that it was inferring the else branch on line 396 to be unreachable.

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Still feels like a mypy bug to me, but your fix is fine.

for target in self.pseudos[thing.name].targets:
for idx, target in enumerate(self.pseudos[thing.name].targets):
target_instr = self.instrs.get(target)
assert target_instr
if format is None:
if idx == 0:
format = target_instr.instr_fmt
else:
assert format == target_instr.instr_fmt
assert format is not None
case _:
typing.assert_never(thing)
assert_never(thing)
all_formats.add(format)
Comment on lines +389 to 395
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And ditto here for format.


# Turn it into a sorted list of enum values.
Expand Down Expand Up @@ -488,7 +481,7 @@ def write_metadata(self, metadata_filename: str, pymetadata_filename: str) -> No
self.pseudo_instrs[thing.name]
)
case _:
typing.assert_never(thing)
assert_never(thing)

with self.metadata_item(
"const struct opcode_macro_expansion "
Expand Down Expand Up @@ -525,7 +518,7 @@ def write_metadata(self, metadata_filename: str, pymetadata_filename: str) -> No
case parsing.Pseudo():
pass
case _:
typing.assert_never(thing)
assert_never(thing)

with self.metadata_item(
"const char * const _PyOpcode_uop_name[OPCODE_UOP_NAME_SIZE]", "=", ";"
Expand Down Expand Up @@ -774,7 +767,7 @@ def write_instructions(
case parsing.Pseudo():
pass
case _:
typing.assert_never(thing)
assert_never(thing)

print(
f"Wrote {n_instrs} instructions and {n_macros} macros "
Expand Down Expand Up @@ -818,7 +811,7 @@ def write_executor_instructions(
case parsing.Pseudo():
pass
case _:
typing.assert_never(thing)
assert_never(thing)
print(
f"Wrote {n_instrs} instructions and {n_uops} ops to {executor_filename}",
file=sys.stderr,
Expand Down Expand Up @@ -850,7 +843,7 @@ def write_abstract_interpreter_instructions(
case parsing.Pseudo():
pass
case _:
typing.assert_never(thing)
assert_never(thing)
print(
f"Wrote some stuff to {abstract_interpreter_filename}",
file=sys.stderr,
Expand Down
9 changes: 4 additions & 5 deletions Tools/cases_generator/mypy.ini
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Original file line number Diff line number Diff line change
Expand Up @@ -2,13 +2,12 @@
files = Tools/cases_generator/
pretty = True

# Make sure Python can still be built
# using Python 3.10 for `PYTHON_FOR_REGEN`...
python_version = 3.10

# Be strict:
# ...And be strict:
strict = True
strict_concatenate = True
enable_error_code = ignore-without-code,redundant-expr,truthy-bool

# Don't enable this one yet;
# it has a lot of false positives on `cases_generator`
warn_unreachable = False
warn_unreachable = True