gh-108455: Run `mypy` on `Tools/peg_generator` (#108456)

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

.github/workflows/mypy.yml

diff --git a/.github/workflows/mypy.yml b/.github/workflows/mypy.yml
index 75264c8..82714c2 100644
--- a/.github/workflows/mypy.yml
+++ b/.github/workflows/mypy.yml
@@ -9,6 +9,7 @@
     paths:
       - "Tools/clinic/**"
       - "Tools/cases_generator/**"
+      - "Tools/peg_generator/**"
       - "Tools/requirements-dev.txt"
       - ".github/workflows/mypy.yml"
   workflow_dispatch:
@@ -29,7 +30,11 @@
   mypy:
     strategy:
       matrix:
-        target: ["Tools/cases_generator", "Tools/clinic"]
+        target: [
+          "Tools/cases_generator",
+          "Tools/clinic",
+          "Tools/peg_generator",
+        ]
     name: Run mypy on ${{ matrix.target }}
     runs-on: ubuntu-latest
     timeout-minutes: 10

Tools/peg_generator/mypy.ini

diff --git a/Tools/peg_generator/mypy.ini b/Tools/peg_generator/mypy.ini
index 1732372..186e633 100644
--- a/Tools/peg_generator/mypy.ini
+++ b/Tools/peg_generator/mypy.ini
@@ -1,5 +1,6 @@
 [mypy]
-files = pegen
+files = Tools/peg_generator/pegen
+pretty = True
 
 follow_imports = error
 no_implicit_optional = True
@@ -24,3 +25,6 @@
 
 [mypy-pegen.grammar_parser]
 strict_optional = False
+
+[mypy-setuptools.*]
+ignore_missing_imports = True

Tools/peg_generator/pegen/build.py

diff --git a/Tools/peg_generator/pegen/build.py b/Tools/peg_generator/pegen/build.py
index e41330f..81efcad 100644
--- a/Tools/peg_generator/pegen/build.py
+++ b/Tools/peg_generator/pegen/build.py
@@ -5,7 +5,7 @@
 import sysconfig
 import tempfile
 import tokenize
-from typing import IO, Dict, List, Optional, Set, Tuple
+from typing import IO, Any, Dict, List, Optional, Set, Tuple
 
 from pegen.c_generator import CParserGenerator
 from pegen.grammar import Grammar
@@ -18,6 +18,7 @@
 MOD_DIR = pathlib.Path(__file__).resolve().parent
 
 TokenDefinitions = Tuple[Dict[int, str], Dict[str, int], Set[str]]
+Incomplete = Any  # TODO: install `types-setuptools` and remove this alias
 
 
 def get_extra_flags(compiler_flags: str, compiler_py_flags_nodist: str) -> List[str]:
@@ -28,7 +29,7 @@ def get_extra_flags(compiler_flags: str, compiler_py_flags_nodist: str) -> List[
     return f"{flags} {py_flags_nodist}".split()
 
 
-def fixup_build_ext(cmd):
+def fixup_build_ext(cmd: Incomplete) -> None:
     """Function needed to make build_ext tests pass.
 
     When Python was built with --enable-shared on Unix, -L. is not enough to
@@ -74,7 +75,7 @@ def compile_c_extension(
     keep_asserts: bool = True,
     disable_optimization: bool = False,
     library_dir: Optional[str] = None,
-) -> str:
+) -> pathlib.Path:
     """Compile the generated source for a parser generator into an extension module.
 
     The extension module will be generated in the same directory as the provided path

Tools/peg_generator/pegen/keywordgen.py

diff --git a/Tools/peg_generator/pegen/keywordgen.py b/Tools/peg_generator/pegen/keywordgen.py
index bbf1326..82d717b 100644
--- a/Tools/peg_generator/pegen/keywordgen.py
+++ b/Tools/peg_generator/pegen/keywordgen.py
@@ -35,6 +35,7 @@
 issoftkeyword = frozenset(softkwlist).__contains__
 '''.lstrip()
 
+
 def main() -> None:
     parser = argparse.ArgumentParser(
         description="Generate the Lib/keywords.py file from the grammar."

Tools/peg_generator/pegen/parser.py

diff --git a/Tools/peg_generator/pegen/parser.py b/Tools/peg_generator/pegen/parser.py
index 034e8e6..eab48ef 100644
--- a/Tools/peg_generator/pegen/parser.py
+++ b/Tools/peg_generator/pegen/parser.py
@@ -10,7 +10,6 @@
 from pegen.tokenizer import Mark, Tokenizer, exact_token_types
 
 T = TypeVar("T")
-P = TypeVar("P", bound="Parser")
 F = TypeVar("F", bound=Callable[..., Any])
 
 
@@ -21,7 +20,7 @@ def logger(method: F) -> F:
     """
     method_name = method.__name__
 
-    def logger_wrapper(self: P, *args: object) -> T:
+    def logger_wrapper(self: "Parser", *args: object) -> Any:
         if not self._verbose:
             return method(self, *args)
         argsr = ",".join(repr(arg) for arg in args)
@@ -41,7 +40,7 @@ def memoize(method: F) -> F:
     """Memoize a symbol method."""
     method_name = method.__name__
 
-    def memoize_wrapper(self: P, *args: object) -> T:
+    def memoize_wrapper(self: "Parser", *args: object) -> Any:
         mark = self._mark()
         key = mark, method_name, args
         # Fast path: cache hit, and not verbose.
@@ -74,11 +73,13 @@ def memoize_wrapper(self: P, *args: object) -> T:
     return cast(F, memoize_wrapper)
 
 
-def memoize_left_rec(method: Callable[[P], Optional[T]]) -> Callable[[P], Optional[T]]:
+def memoize_left_rec(
+    method: Callable[["Parser"], Optional[T]]
+) -> Callable[["Parser"], Optional[T]]:
     """Memoize a left-recursive symbol method."""
     method_name = method.__name__
 
-    def memoize_left_rec_wrapper(self: P) -> Optional[T]:
+    def memoize_left_rec_wrapper(self: "Parser") -> Optional[T]:
         mark = self._mark()
         key = mark, method_name, ()
         # Fast path: cache hit, and not verbose.

Tools/requirements-dev.txt

diff --git a/Tools/requirements-dev.txt b/Tools/requirements-dev.txt
index 111773f..b814169 100644
--- a/Tools/requirements-dev.txt
+++ b/Tools/requirements-dev.txt
@@ -1,3 +1,3 @@
 # Requirements file for external linters and checks we run on
-# Tools/clinic and Tools/cases_generator/ in CI
+# Tools/clinic, Tools/cases_generator/, and Tools/peg_generator/ in CI
 mypy==1.5.1