python · ilevkivskyi · Feb 17, 2026 · Feb 17, 2026 · Feb 17, 2026 · Feb 17, 2026
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
@@ -106,17 +106,20 @@ jobs:
           os: ubuntu-24.04-arm
           toxenv: py
           tox_extra_args: "-n 4 --mypy-num-workers=4 mypy/test/testcheck.py"
+          dev_ast_serialize: true
         - name: Parallel tests with py314-ubuntu, mypyc-compiled
           python: '3.14'
           os: ubuntu-24.04-arm
           toxenv: py
           tox_extra_args: "-n 4 --mypy-num-workers=4 mypy/test/testcheck.py"
           test_mypyc: true
-        - name: Parallel tests with py314-windows-64, interpreted
-          python: '3.14'
-          os: windows-latest
-          toxenv: py
-          tox_extra_args: "-n 2 --mypy-num-workers=2 mypy/test/testcheck.py -k 'incremental or modules or classes'"
+          dev_ast_serialize: true
+        # Skip Windows tests until we publish ast_serialize wheels on PyPI.
+        # - name: Parallel tests with py314-windows-64, interpreted
+        #   python: '3.14'
+        #   os: windows-latest
+        #   toxenv: py
+        #   tox_extra_args: "-n 2 --mypy-num-workers=2 mypy/test/testcheck.py -k 'incremental or modules or classes'"
 
         - name: Type check our own code (py310-ubuntu)
           python: '3.10'
@@ -139,6 +142,7 @@ jobs:
     timeout-minutes: 60
     env:
       TOX_SKIP_MISSING_INTERPRETERS: False
+      VIRTUALENV_SYSTEM_SITE_PACKAGES: ${{ matrix.dev_ast_serialize && 1 || 0 }}
       # Rich (pip) -- Disable color for windows + pytest
       FORCE_COLOR: ${{ !(startsWith(matrix.os, 'windows-') && startsWith(matrix.toxenv, 'py')) && 1 || 0 }}
       # Tox
@@ -213,6 +217,30 @@ jobs:
         pip install -r test-requirements.txt
         CC=clang MYPYC_OPT_LEVEL=0 MYPY_USE_MYPYC=1 pip install -e .
 
+    # To speed-up process until ast_serialize is on PyPI.
+    - name: Checkout pinned ast_serialize
+      if: ${{ matrix.dev_ast_serialize }}
+      uses: actions/checkout@v4
+      with:
+        persist-credentials: false
+        repository: mypyc/ast_serialize
+        ref: da5a16cf268dbec63ed6b2e6b715470576e2d1a6
+        path: ast_serialize
+
+    - if: ${{ matrix.dev_ast_serialize }}
+      uses: PyO3/maturin-action@v1
+      with:
+        target: aarch64
+        args: --release --out dist
+        working-directory: ast_serialize
+
+    - if: ${{ matrix.dev_ast_serialize }}
+      run: |
+        pip install ast_serialize/dist/ast_serialize-0.1.0-cp39-abi3-manylinux_2_34_aarch64.whl
+        echo 'no way' > test_ast_serialize.py
+        python3 -c 'import ast_serialize; print(ast_serialize.parse("test_ast_serialize.py")[1])'
+        rm test_ast_serialize.py
+
     - name: Setup tox environment
       run: |
         tox run -e ${{ matrix.toxenv }} --notest

diff --git a/mypy/message_registry.py b/mypy/message_registry.py
@@ -303,7 +303,7 @@ def with_additional_msg(self, info: str) -> ErrorMessage:
     "Condition can't be inferred, unable to merge overloads"
 )
 TYPE_IGNORE_WITH_ERRCODE_ON_MODULE: Final = ErrorMessage(
-    "type ignore with error code is not supported for modules; "
+    "Type ignore with error code is not supported for modules; "
     'use `# mypy: disable-error-code="{}"`',
     codes.SYNTAX,
 )

diff --git a/mypy/test/testcheck.py b/mypy/test/testcheck.py
@@ -141,12 +141,16 @@ def run_case_once(
 
         if options.num_workers:
             options.fixed_format_cache = True
+            options.native_parser = True
             if testcase.output_files:
                 raise pytest.skip("Reports are not supported in parallel mode")
             # Note: do not use this unless really needed!
             if testcase.name.endswith("_no_parallel"):
                 raise pytest.skip("Test not supported in parallel mode yet")
 
+        if options.native_parser and testcase.name.endswith("_no_native_parse"):
+            raise pytest.skip("Test not supported by native parser yet")
+
         # Enable some options automatically based on test file name.
         if "columns" in testcase.file:
             options.show_column_numbers = True

diff --git a/test-data/unit/check-annotated.test b/test-data/unit/check-annotated.test
@@ -17,7 +17,7 @@ x: Annotated[int, THESE, ARE, IGNORED, FOR, NOW]
 reveal_type(x)  # N: Revealed type is "builtins.int"
 [builtins fixtures/tuple.pyi]
 
-[case testAnnotated3]
+[case testAnnotated3_no_native_parse]
 from typing_extensions import Annotated
 x: Annotated[int, -+~12.3, "som"[e], more(anno+a+ions, that=[are]), (b"ignored",), 4, N.O.W, ...]
 reveal_type(x)  # N: Revealed type is "builtins.int"

diff --git a/test-data/unit/check-async-await.test b/test-data/unit/check-async-await.test
@@ -192,7 +192,7 @@ async def f() -> None:
 [builtins fixtures/async_await.pyi]
 [typing fixtures/typing-async.pyi]
 
-[case testAsyncForTypeComments]
+[case testAsyncForTypeComments_no_native_parse]
 
 from typing import AsyncIterator, Union
 class C(AsyncIterator[int]):
@@ -342,7 +342,7 @@ async def f() -> None:
 [builtins fixtures/async_await.pyi]
 [typing fixtures/typing-async.pyi]
 
-[case testAsyncWithTypeComments]
+[case testAsyncWithTypeComments_no_native_parse]
 
 class C:
     async def __aenter__(self) -> int: pass

diff --git a/test-data/unit/check-basic.test b/test-data/unit/check-basic.test
@@ -286,7 +286,7 @@ x = 1
 x in 1,  # E: Unsupported right operand type for in ("int")
 [builtins fixtures/tuple.pyi]
 
-[case testTrailingCommaInIfParsing]
+[case testTrailingCommaInIfParsing_no_native_parse]
 if x in 1, : pass
 [out]
 main:1: error: Invalid syntax

diff --git a/test-data/unit/check-columns.test b/test-data/unit/check-columns.test
@@ -1,6 +1,6 @@
 # Test column numbers in messages. --show-column-numbers is enabled implicitly by test runner.
 
-[case testColumnsSyntaxError]
+[case testColumnsSyntaxError_no_native_parse]
 f()
 1 +
 [out]
@@ -146,7 +146,7 @@ if int():
     def f(a: 'A') -> None: pass
     (f(b=object())) # E:6: Unexpected keyword argument "b" for "f"
 
-[case testColumnInvalidType]
+[case testColumnInvalidType_no_native_parse]
 
 from typing import Iterable
 
@@ -342,7 +342,7 @@ if int():
 main:2:11: error: Syntax error in type annotation
 main:2:11: note: Suggestion: Is there a spurious trailing comma?
 
-[case testColumnSyntaxErrorInTypeAnnotation2]
+[case testColumnSyntaxErrorInTypeAnnotation2_no_native_parse]
 if int():
     # TODO: It would be better to point to the type comment
     xyz = 0  # type: blurbnard blarb

diff --git a/test-data/unit/check-errorcodes.test b/test-data/unit/check-errorcodes.test
@@ -30,21 +30,21 @@ class A:
 [case testErrorCodeNoteHasNoCode]
 reveal_type(1) # N: Revealed type is "Literal[1]?"
 
-[case testErrorCodeSyntaxError]
+[case testErrorCodeSyntaxError_no_native_parse]
 1 ''
 [out]
 main:1: error: Invalid syntax  [syntax]
 [out version==3.10.0]
 main:1: error: Invalid syntax. Perhaps you forgot a comma?  [syntax]
 
-[case testErrorCodeSyntaxError2]
+[case testErrorCodeSyntaxError2_no_native_parse]
 def f(): # E: Type signature has too many parameters  [syntax]
     # type: (int) -> None
     1
 
 x = 0  # type: x y  # E: Syntax error in type comment "x y"  [syntax]
 
-[case testErrorCodeSyntaxError3]
+[case testErrorCodeSyntaxError3_no_native_parse]
 # This is a bit inconsistent -- syntax error would be more logical?
 x: 'a b'  # E: Invalid type comment or annotation  [valid-type]
 for v in x:  # type: int, int  # E: Syntax error in type annotation  [syntax] \
@@ -208,7 +208,7 @@ def h(x  # type: xyz  # type: ignore[foo]  # E: Name "xyz" is not defined  [name
 import nostub  # type: ignore[import]
 from defusedxml import xyz  # type: ignore[import]
 
-[case testErrorCodeBadIgnore]
+[case testErrorCodeBadIgnore_no_native_parse]
 import nostub # type: ignore xyz  # E: Invalid "type: ignore" comment  [syntax] \
                                   # E: Cannot find implementation or library stub for module named "nostub"  [import-not-found] \
                                   # N: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports
@@ -226,7 +226,7 @@ def f(x,  # type: int  # type: ignore[  # E: Invalid "type: ignore" comment  [sy
     # type: (...) -> None
     pass
 
-[case testErrorCodeBadIgnoreNoExtraComment]
+[case testErrorCodeBadIgnoreNoExtraComment_no_native_parse]
 # Omit the E: ... comments, as they affect parsing
 import nostub # type: ignore xyz
 import nostub # type: ignore[xyz
@@ -762,7 +762,7 @@ main:1: error: Name "y" is not defined  [name-defined]
 main:2: error: Name "ignored" is not defined  [name-defined]
 main:2: error: Name "y" is not defined  [name-defined]
 
-[case testErrorCodeTypeIgnoreMisspelled2]
+[case testErrorCodeTypeIgnoreMisspelled2_no_native_parse]
 x = y  # type: int  # type: ignored[foo]
 x = y  # type: int  # type: ignored [foo]
 [out]
@@ -1014,7 +1014,7 @@ def f(arg: int) -> int:
 def f(arg: str) -> str:
     ...
 
-[case testSliceInDictBuiltin]
+[case testSliceInDictBuiltin_no_native_parse]
 # flags: --show-column-numbers
 b: dict[int, x:y]
 c: dict[x:y]
@@ -1027,7 +1027,7 @@ main:3:4: error: "dict" expects 2 type arguments, but 1 given  [type-arg]
 main:3:9: error: Invalid type comment or annotation  [valid-type]
 main:3:9: note: did you mean to use ',' instead of ':' ?
 
-[case testSliceInDictTyping]
+[case testSliceInDictTyping_no_native_parse]
 # flags: --show-column-numbers
 from typing import Dict
 b: Dict[int, x:y]
@@ -1067,11 +1067,11 @@ def f(d: D, s: str) -> None:
 [typing fixtures/typing-typeddict.pyi]
 
 [case testRecommendErrorCode]
-# type: ignore[whatever]  # E: type ignore with error code is not supported for modules; use `# mypy: disable-error-code="whatever"`  [syntax]
+# type: ignore[whatever]  # E: Type ignore with error code is not supported for modules; use `# mypy: disable-error-code="whatever"`  [syntax]
 1 + "asdf"
 
 [case testRecommendErrorCode2]
-# type: ignore[whatever, other]  # E: type ignore with error code is not supported for modules; use `# mypy: disable-error-code="whatever, other"`  [syntax]
+# type: ignore[whatever, other]  # E: Type ignore with error code is not supported for modules; use `# mypy: disable-error-code="whatever, other"`  [syntax]
 1 + "asdf"
 
 [case testShowErrorCodesInConfig]

diff --git a/test-data/unit/check-expressions.test b/test-data/unit/check-expressions.test
@@ -1456,7 +1456,7 @@ if int():
     b = (x for x in a)  # E: Generator has incompatible item type "Callable[[], str]"; expected "Callable[[], int]"
 [builtins fixtures/list.pyi]
 
-[case testGeneratorNoSpuriousError]
+[case testGeneratorNoSpuriousError_no_native_parse]
 from typing import Iterable, overload
 
 @overload
@@ -1915,7 +1915,7 @@ None == None
 None < None  # E: Unsupported left operand type for < ("None")
 [builtins fixtures/ops.pyi]
 
-[case testDictWithStarExpr]
+[case testDictWithStarExpr_no_native_parse]
 
 b = {'z': 26, *a}  # E: Invalid syntax
 [builtins fixtures/dict.pyi]

diff --git a/test-data/unit/check-fastparse.test b/test-data/unit/check-fastparse.test
@@ -1,8 +1,8 @@
-[case testFastParseSyntaxError]
+[case testFastParseSyntaxError_no_native_parse]
 
 1 +  # E: Invalid syntax
 
-[case testFastParseTypeCommentSyntaxError]
+[case testFastParseTypeCommentSyntaxError_no_native_parse]
 
 x = None # type: a : b  # E: Syntax error in type comment "a : b"
 
@@ -12,13 +12,13 @@ x = None # type: a + b  # E: Invalid type comment or annotation
 
 -- Function type comments are attributed to the function def line.
 -- This happens in both parsers.
-[case testFastParseFunctionAnnotationSyntaxError]
+[case testFastParseFunctionAnnotationSyntaxError_no_native_parse]
 
 def f():  # E: Syntax error in type comment "None -> None" # N: Suggestion: wrap argument types in parentheses
   # type: None -> None
   pass
 
-[case testFastParseFunctionAnnotationSyntaxErrorSpaces]
+[case testFastParseFunctionAnnotationSyntaxErrorSpaces_no_native_parse]
 
 def f():  # E: Syntax error in type comment "None -> None" # N: Suggestion: wrap argument types in parentheses
   # type:             None -> None
@@ -156,7 +156,7 @@ def f(a,        # type: A
 [builtins fixtures/dict.pyi]
 [out]
 
-[case testFastParsePerArgumentAnnotationsWithAnnotatedBareStar]
+[case testFastParsePerArgumentAnnotationsWithAnnotatedBareStar_no_native_parse]
 
 def f(*, # type: int  # E: Bare * has associated type comment
       x  # type: str
@@ -194,7 +194,7 @@ def f(x, y):  # E: Type signature has too few parameters
 f(1, 2)
 f(1) # E: Missing positional argument "y" in call to "f"
 
-[case testFasterParseTypeErrorCustom]
+[case testFasterParseTypeErrorCustom_no_native_parse]
 
 from typing import TypeVar, Generic
 T = TypeVar('T')
@@ -275,7 +275,7 @@ def f7(x: int):  # E: Function has duplicate type signatures
   # type: (int) -> int
   pass
 
-[case testFastParserDuplicateNames]
+[case testFastParserDuplicateNames_no_native_parse]
 
 def f(x, y, z):
   pass

diff --git a/test-data/unit/check-functions.test b/test-data/unit/check-functions.test
@@ -774,7 +774,7 @@ class A:
 main:6: error: Incompatible types in assignment (expression has type "int", variable has type "A")
 main:8: error: Argument 1 to "g" has incompatible type "A"; expected "int"
 
-[case testNestedFunctionInMethodWithTooFewArgumentsInTypeComment]
+[case testNestedFunctionInMethodWithTooFewArgumentsInTypeComment_no_native_parse]
 class A:
     def f(self):
         # type: () -> None
@@ -795,7 +795,7 @@ class A:
             arg.B  # E: "object" has no attribute "B"
 [file mod.py]
 
-[case testDeepNestedFunctionWithTooFewArgumentsInTypeComment]
+[case testDeepNestedFunctionWithTooFewArgumentsInTypeComment_no_native_parse]
 class A:
     def f(self):
         # type: () -> None
@@ -2139,13 +2139,13 @@ class A:
         pass
 [builtins fixtures/staticmethod.pyi]
 
-[case testEllipsisWithSomethingAfterItFails]
+[case testEllipsisWithSomethingAfterItFails_no_native_parse]
 def f(x, y, z): # type: (..., int) -> None
     pass
 [out]
 main:1: error: Ellipses cannot accompany other parameter types in function type signature
 
-[case testEllipsisWithSomethingBeforeItFails]
+[case testEllipsisWithSomethingBeforeItFails_no_native_parse]
 def f(x, y, z): # type: (int, ...) -> None
     pass
 [out]

diff --git a/test-data/unit/check-ignore.test b/test-data/unit/check-ignore.test
@@ -32,7 +32,7 @@ from xyz_m import * # type: ignore
 x   # E: Name "x" is not defined
 1() # E: "int" not callable
 
-[case testIgnoreImportBadModule]
+[case testIgnoreImportBadModule_no_native_parse]
 import m # type: ignore
 from m import a # type: ignore
 [file m.py]
@@ -54,7 +54,7 @@ foo = 3
 [builtins fixtures/module_all.pyi]
 [out]
 
-[case testIgnoreImportStarFromBadModule]
+[case testIgnoreImportStarFromBadModule_no_native_parse]
 from m import * # type: ignore
 [file m.py]
 +

diff --git a/test-data/unit/check-incremental.test b/test-data/unit/check-incremental.test
@@ -7264,7 +7264,7 @@ bar: int = foo
 [out3]
 tmp/bar.py:2: error: Incompatible types in assignment (expression has type "str", variable has type "int")
 
-[case testIncrementalBlockingErrorRepeatAndUndo]
+[case testIncrementalBlockingErrorRepeatAndUndo_no_native_parse]
 import m
 [file m.py]
 import f