Add invalidation-mode option

src/_pytest/assertion/__init__.py

@@ -83,6 +83,7 @@ class AssertionState:
     def __init__(self, config: Config, mode) -> None:
         self.mode = mode
         self.trace = config.trace.root.get("assertion")
+        self.invalidation_mode = config.option.invalidationmode
         self.hook: Optional[rewrite.AssertionRewritingHook] = None
 
 

src/_pytest/assertion/rewrite.py

@@ -1,4 +1,5 @@
 """Rewrite assertion AST to produce nice error messages."""
+import _imp
 import ast
 import errno
 import functools
@@ -21,6 +22,7 @@
 from typing import Iterable
 from typing import Iterator
 from typing import List
+from typing import Literal
 from typing import Optional
 from typing import Sequence
 from typing import Set
@@ -290,23 +292,31 @@ def get_resource_reader(self, name: str) -> TraversableResources:  # type: ignor
 
 
 def _write_pyc_fp(
-    fp: IO[bytes], source_stat: os.stat_result, source_hash: bytes, co: types.CodeType
+    fp: IO[bytes],
+    source_stat: os.stat_result,
+    source_hash: bytes,
+    co: types.CodeType,
+    invalidation_mode: Literal["timestamp", "checked-hash"],
 ) -> None:
     # Technically, we don't have to have the same pyc format as
     # (C)Python, since these "pycs" should never be seen by builtin
     # import. However, there's little reason to deviate.
     fp.write(importlib.util.MAGIC_NUMBER)
     # https://www.python.org/dev/peps/pep-0552/
-    flags = b"\x00\x00\x00\x00"
-    fp.write(flags)
-    # as of now, bytecode header expects 32-bit numbers for size and mtime (#4903)
-    mtime = int(source_stat.st_mtime) & 0xFFFFFFFF
-    size = source_stat.st_size & 0xFFFFFFFF
-    # 64-bit source file hash
-    source_hash = source_hash[:8]
-    # "<LL" stands for 2 unsigned longs, little-endian.
-    fp.write(struct.pack("<LL", mtime, size))
-    fp.write(source_hash)
+    if invalidation_mode == "timestamp":
+        flags = b"\x00\x00\x00\x00"
+        fp.write(flags)
+        # as of now, bytecode header expects 32-bit numbers for size and mtime (#4903)
+        mtime = int(source_stat.st_mtime) & 0xFFFFFFFF
+        size = source_stat.st_size & 0xFFFFFFFF
+        # "<LL" stands for 2 unsigned longs, little-endian.
+        fp.write(struct.pack("<LL", mtime, size))
+    elif invalidation_mode == "checked-hash":
+        flags = b"\x03\x00\x00\x00"
+        fp.write(flags)
+        # 64-bit source file hash
+        source_hash = source_hash[:8]
+        fp.write(source_hash)
     fp.write(marshal.dumps(co))
 
 
@@ -320,7 +330,7 @@ def _write_pyc(
     proc_pyc = f"{pyc}.{os.getpid()}"
     try:
         with open(proc_pyc, "wb") as fp:
-            _write_pyc_fp(fp, source_stat, source_hash, co)
+            _write_pyc_fp(fp, source_stat, source_hash, co, state.invalidation_mode)
     except OSError as e:
         state.trace(f"error writing pyc file at {proc_pyc}: errno={e.errno}")
         return False
@@ -367,35 +377,41 @@ def _read_pyc(
             stat_result = os.stat(source)
             mtime = int(stat_result.st_mtime)
             size = stat_result.st_size
-            data = fp.read(24)
+            data = fp.read(16)
         except OSError as e:
             trace(f"_read_pyc({source}): OSError {e}")
             return None
         # Check for invalid or out of date pyc file.
-        if len(data) != (24):
+        if len(data) != (16):
             trace("_read_pyc(%s): invalid pyc (too short)" % source)
             return None
         if data[:4] != importlib.util.MAGIC_NUMBER:
             trace("_read_pyc(%s): invalid pyc (bad magic number)" % source)
             return None
-        if data[4:8] != b"\x00\x00\x00\x00":
-            trace("_read_pyc(%s): invalid pyc (unsupported flags)" % source)
-            return None
-        size_data = data[12:16]
-        if int.from_bytes(size_data, "little") != size & 0xFFFFFFFF:
-            trace("_read_pyc(%s): invalid pyc (incorrect size)" % source)
-            return None
-        mtime_data = data[8:12]
-        if int.from_bytes(mtime_data, "little") != mtime & 0xFFFFFFFF:
-            trace("_read_pyc(%s): out of date" % source)
-            hash = data[16:24]
+
+        hash_based = getattr(_imp, "check_hash_based_pycs", "default") == "always"
+        if data[4:8] == b"\x00\x00\x00\x00" and not hash_based:
+            trace("_read_pyc(%s): timestamp based" % source)
+            mtime_data = data[8:12]
+            if int.from_bytes(mtime_data, "little") != mtime & 0xFFFFFFFF:
+                trace("_read_pyc(%s): out of date" % source)
+                return None
+            size_data = data[12:16]
+            if int.from_bytes(size_data, "little") != size & 0xFFFFFFFF:
+                trace("_read_pyc(%s): invalid pyc (incorrect size)" % source)
+                return None
+        elif data[4:8] == b"\x03\x00\x00\x00":
+            trace("_read_pyc(%s): hash based" % source)
+            hash = data[8:16]
             # source_hash returns bytes not int: https://github.com/python/typeshed/pull/10686
             source_hash: bytes = importlib.util.source_hash(source.read_bytes())  # type: ignore[assignment]
-            if source_hash[:8] == hash:
-                trace("_read_pyc(%s): source hash match (no change detected)" % source)
-            else:
+            if source_hash[:8] != hash:
                 trace("_read_pyc(%s): hash doesn't match" % source)
                 return None
+        else:
+            trace("_read_pyc(%s): invalid pyc (unsupported flags)" % source)
+            return None
+
         try:
             co = marshal.load(fp)
         except Exception as e:

src/_pytest/main.py

@@ -215,6 +215,13 @@ def pytest_addoption(parser: Parser) -> None:
         help="Prepend/append to sys.path when importing test modules and conftest "
         "files. Default: prepend.",
     )
+    group.addoption(
+        "--invalidation-mode",
+        default="timestamp",
+        choices=["timestamp", "checked-hash"],
+        dest="invalidationmode",
+        help="Pytest pyc cache invalidation mode. Default: timestamp.",
+    )
 
     group = parser.getgroup("debugconfig", "test session debugging and configuration")
     group.addoption(

testing/test_assertrewrite.py

@@ -1,3 +1,4 @@
+import _imp
 import ast
 import errno
 import glob
@@ -1124,13 +1125,37 @@ def test_read_pyc_success(self, tmp_path: Path, pytester: Pytester) -> None:
         _write_pyc(state, co, source_stat, hash, pyc)
         assert _read_pyc(fn, pyc, state.trace) is not None
 
-        # pyc read should still work if only the mtime changed
-        # Fallback to hash comparison
-        new_mtime = source_stat.st_mtime + 1.2
-        os.utime(fn, (new_mtime, new_mtime))
-        assert source_stat.st_mtime != os.stat(fn).st_mtime
+        pyc_bytes = pyc.read_bytes()
+        assert pyc_bytes[4] == 0  # timestamp flag set
+
+    def test_read_pyc_success_hash(self, tmp_path: Path, pytester: Pytester) -> None:
+        from _pytest.assertion import AssertionState
+        from _pytest.assertion.rewrite import _read_pyc
+        from _pytest.assertion.rewrite import _rewrite_test
+        from _pytest.assertion.rewrite import _write_pyc
+
+        config = pytester.parseconfig("--invalidation-mode=checked-hash")
+        state = AssertionState(config, "rewrite")
+
+        fn = tmp_path / "source.py"
+        pyc = Path(str(fn) + "c")
+
+        # Test private attribute didn't change
+        assert getattr(_imp, "check_hash_based_pycs", None) in {
+            "default",
+            "always",
+            "never",
+        }
+
+        fn.write_text("def test(): assert True", encoding="utf-8")
+        source_stat, hash, co = _rewrite_test(fn, config)
+        _write_pyc(state, co, source_stat, hash, pyc)
         assert _read_pyc(fn, pyc, state.trace) is not None
 
+        pyc_bytes = pyc.read_bytes()
+        assert pyc_bytes[4] == 3  # checked-hash flag set
+        assert pyc_bytes[8:16] == hash
+
     def test_read_pyc_more_invalid(self, tmp_path: Path) -> None:
         from _pytest.assertion.rewrite import _read_pyc
 
@@ -1149,36 +1174,78 @@ def test_read_pyc_more_invalid(self, tmp_path: Path) -> None:
         os.utime(source, (mtime_int, mtime_int))
 
         size = len(source_bytes).to_bytes(4, "little")
-        # source_hash returns bytes not int: https://github.com/python/typeshed/pull/10686
-        hash: bytes = source_hash(source_bytes)  # type: ignore[assignment]
-        hash = hash[:8]
 
         code = marshal.dumps(compile(source_bytes, str(source), "exec"))
 
         # Good header.
-        pyc.write_bytes(magic + flags + mtime + size + hash + code)
+        pyc.write_bytes(magic + flags + mtime + size + code)
         assert _read_pyc(source, pyc, print) is not None
 
         # Too short.
         pyc.write_bytes(magic + flags + mtime)
         assert _read_pyc(source, pyc, print) is None
 
         # Bad magic.
-        pyc.write_bytes(b"\x12\x34\x56\x78" + flags + mtime + size + hash + code)
+        pyc.write_bytes(b"\x12\x34\x56\x78" + flags + mtime + size + code)
         assert _read_pyc(source, pyc, print) is None
 
         # Unsupported flags.
-        pyc.write_bytes(magic + b"\x00\xff\x00\x00" + mtime + size + hash + code)
+        pyc.write_bytes(magic + b"\x00\xff\x00\x00" + mtime + size + code)
         assert _read_pyc(source, pyc, print) is None
 
-        # Bad size.
-        pyc.write_bytes(magic + flags + mtime + b"\x99\x00\x00\x00" + hash + code)
+        # Bad mtime.
+        pyc.write_bytes(magic + flags + b"\x58\x3d\xb0\x5f" + size + code)
         assert _read_pyc(source, pyc, print) is None
 
-        # Bad mtime + bad hash.
-        pyc.write_bytes(magic + flags + b"\x58\x3d\xb0\x5f" + size + b"\x00" * 8 + code)
+        # Bad size.
+        pyc.write_bytes(magic + flags + mtime + b"\x99\x00\x00\x00" + code)
         assert _read_pyc(source, pyc, print) is None
 
+    def test_read_pyc_more_invalid_hash(self, tmp_path: Path) -> None:
+        from _pytest.assertion.rewrite import _read_pyc
+
+        source = tmp_path / "source.py"
+        pyc = tmp_path / "source.pyc"
+
+        source_bytes = b"def test(): pass\n"
+        source.write_bytes(source_bytes)
+
+        magic = importlib.util.MAGIC_NUMBER
+
+        flags = b"\x00\x00\x00\x00"
+        flags_hash = b"\x03\x00\x00\x00"
+
+        mtime = b"\x58\x3c\xb0\x5f"
+        mtime_int = int.from_bytes(mtime, "little")
+        os.utime(source, (mtime_int, mtime_int))
+
+        size = len(source_bytes).to_bytes(4, "little")
+
+        # source_hash returns bytes not int: https://github.com/python/typeshed/pull/10686
+        hash: bytes = source_hash(source_bytes)  # type: ignore[assignment]
+        hash = hash[:8]
+
+        code = marshal.dumps(compile(source_bytes, str(source), "exec"))
+
+        # check_hash_based_pycs == "default" with hash based pyc file.
+        pyc.write_bytes(magic + flags_hash + hash + code)
+        assert _read_pyc(source, pyc, print) is not None
+
+        # check_hash_based_pycs == "always" with hash based pyc file.
+        with mock.patch.object(_imp, "check_hash_based_pycs", "always"):
+            pyc.write_bytes(magic + flags_hash + hash + code)
+            assert _read_pyc(source, pyc, print) is not None
+
+        # Bad hash.
+        with mock.patch.object(_imp, "check_hash_based_pycs", "always"):
+            pyc.write_bytes(magic + flags_hash + b"\x00" * 8 + code)
+            assert _read_pyc(source, pyc, print) is None
+
+        # check_hash_based_pycs == "always" with timestamp based pyc file.
+        with mock.patch.object(_imp, "check_hash_based_pycs", "always"):
+            pyc.write_bytes(magic + flags + mtime + size + code)
+            assert _read_pyc(source, pyc, print) is None
+
     def test_reload_is_same_and_reloads(self, pytester: Pytester) -> None:
         """Reloading a (collected) module after change picks up the change."""
         pytester.makeini(