Introduce a LockfileFormat enum.

src/python/pants/backend/python/goals/pytest_runner_test.py

@@ -13,7 +13,11 @@
 from pants.backend.python.util_rules.interpreter_constraints import InterpreterConstraints
 from pants.backend.python.util_rules.lockfile_metadata import PythonLockfileMetadataV3
 from pants.backend.python.util_rules.pex import PexRequirementsInfo
-from pants.backend.python.util_rules.pex_requirements import LoadedLockfile, Lockfile
+from pants.backend.python.util_rules.pex_requirements import (
+    LoadedLockfile,
+    Lockfile,
+    LockfileFormat,
+)
 from pants.engine.fs import DigestContents, FileContent
 from pants.engine.internals.native_engine import EMPTY_DIGEST
 from pants.testutil.option_util import create_subsystem
@@ -98,7 +102,9 @@ def validate(reqs: list[str]) -> None:
             only_binary=set(),
             no_binary=set(),
         )
-        loaded_lockfile = LoadedLockfile(EMPTY_DIGEST, "", metadata, 0, True, None, lockfile)
+        loaded_lockfile = LoadedLockfile(
+            EMPTY_DIGEST, "", metadata, 0, LockfileFormat.Pex, None, lockfile
+        )
         run_rule_with_mocks(
             validate_pytest_cov_included,
             rule_args=[tool],

src/python/pants/backend/python/subsystems/python_tool_base_test.py

@@ -9,6 +9,7 @@
 from pants.backend.python.util_rules.pex_requirements import (
     LoadedLockfile,
     Lockfile,
+    LockfileFormat,
     PexRequirements,
     Resolve,
 )
@@ -52,7 +53,9 @@ def test_get_lockfile_metadata() -> None:
         no_binary=set(),
     )
     lockfile = Lockfile("dummy_url", "dummy_description_of_origin", "dummy_resolve")
-    loaded_lockfile = LoadedLockfile(EMPTY_DIGEST, "", metadata, 0, True, None, lockfile)
+    loaded_lockfile = LoadedLockfile(
+        EMPTY_DIGEST, "", metadata, 0, LockfileFormat.Pex, None, lockfile
+    )
     assert (
         run_rule_with_mocks(
             get_lockfile_metadata,

src/python/pants/backend/python/util_rules/pex.py

@@ -44,6 +44,7 @@
     LoadedLockfile,
     LoadedLockfileRequest,
     Lockfile,
+    LockfileFormat,
     Resolve,
     ResolvePexConfigRequest,
     determine_resolve_pex_config,
@@ -571,7 +572,7 @@ async def _build_uv_venv(
             uv_request.requirements.from_superset, **implicitly()
         )
         loaded_lockfile = await load_lockfile(LoadedLockfileRequest(lockfile), **implicitly())
-        if loaded_lockfile.is_pex_native:
+        if loaded_lockfile.lockfile_format == LockfileFormat.Pex:
             try:
                 digest_contents = await get_digest_contents(loaded_lockfile.lockfile_digest)
                 lockfile_bytes = next(
@@ -793,7 +794,7 @@ async def _setup_pex_requirements(
     if loaded_lockfile:
         argv = (
             ["--lock", loaded_lockfile.lockfile_path, *pex_lock_resolver_args]
-            if loaded_lockfile.is_pex_native
+            if loaded_lockfile.lockfile_format == LockfileFormat.Pex
             # We use pip to resolve a requirements.txt pseudo-lockfile, possibly with hashes.
             else [
                 "--requirement",
@@ -843,7 +844,7 @@ async def _setup_pex_requirements(
         loaded_lockfile = await load_lockfile(LoadedLockfileRequest(lockfile), **implicitly())
 
         # NB: This is also validated in the constructor.
-        assert loaded_lockfile.is_pex_native
+        assert loaded_lockfile.lockfile_format == LockfileFormat.Pex
         if not reqs_info.req_strings:
             return _BuildPexRequirementsSetup([], [], concurrency_available)
 

src/python/pants/backend/python/util_rules/pex_from_targets.py

@@ -34,6 +34,7 @@
     EntireLockfile,
     LoadedLockfileRequest,
     Lockfile,
+    LockfileFormat,
     PexRequirements,
     Resolve,
     load_lockfile,
@@ -570,7 +571,7 @@ async def _determine_requirements_for_pex_from_targets(
         loaded_lockfile = await load_lockfile(
             LoadedLockfileRequest(chosen_resolve.lockfile), **implicitly()
         )
-        pex_native_subsetting_supported = loaded_lockfile.is_pex_native
+        pex_native_subsetting_supported = loaded_lockfile.lockfile_format == LockfileFormat.Pex
         if loaded_lockfile.as_constraints_strings:
             requirements = dataclasses.replace(
                 requirements,

src/python/pants/backend/python/util_rules/pex_from_targets_test.py

@@ -51,6 +51,7 @@
 )
 from pants.backend.python.util_rules.pex_requirements import (
     EntireLockfile,
+    LockfileFormat,
     PexRequirements,
     Resolve,
 )
@@ -172,10 +173,12 @@ class RequirementMode(Enum):
     global_requirement_constraints = ["constraint1", "constraint2"]
 
     resolve__pex = Resolve("pex", False)
-    loaded_lockfile__pex = Mock(is_pex_native=True, as_constraints_strings=None)
+    loaded_lockfile__pex = Mock(lockfile_format=LockfileFormat.Pex, as_constraints_strings=None)
     chosen_resolve__pex = Mock(lockfile=Mock())
     chosen_resolve__pex.name = "pex"  # name has special meaning in Mock(), so must set it here.
-    loaded_lockfile__not_pex = Mock(is_pex_native=False, as_constraints_strings=req_strings)
+    loaded_lockfile__not_pex = Mock(
+        lockfile_format=LockfileFormat.ConstraintsDeprecated, as_constraints_strings=req_strings
+    )
     chosen_resolve__not_pex = Mock(lockfile=Mock())
     chosen_resolve__not_pex.name = "not_pex"  # ditto.
 

src/python/pants/backend/python/util_rules/pex_requirements.py

@@ -8,6 +8,7 @@
 import logging
 from collections.abc import Iterable, Iterator
 from dataclasses import dataclass, field
+from enum import StrEnum, auto
 from typing import TYPE_CHECKING
 from urllib.parse import urlparse
 
@@ -50,6 +51,13 @@
 logger = logging.getLogger(__name__)
 
 
+class LockfileFormat(StrEnum):
+    Pex = auto()
+    # The very old, deprecated constraints-based "lockfile" that should
+    # be removed entirely.
+    ConstraintsDeprecated = auto()
+
+
 @dataclass(frozen=True)
 class Resolve:
     # A named resolve for a "user lockfile".
@@ -101,10 +109,10 @@ class LoadedLockfile:
     # An estimate of the number of requirements in this lockfile, to be used as a heuristic for
     # available parallelism.
     requirement_estimate: int
-    # True if the loaded lockfile is in PEX's native format.
-    is_pex_native: bool
-    # If !is_pex_native, the lockfile parsed as constraints strings, for use when the lockfile
-    # needs to be subsetted (see #15031, ##12222).
+    # The format of the loaded lockfile.
+    lockfile_format: LockfileFormat
+    # If lockfile_format is ConstraintsDeprecated, the lockfile parsed as constraints strings,
+    # for use when the lockfile needs to be subsetted (see #15031, ##12222).
     as_constraints_strings: FrozenOrderedSet[str] | None
     # The original file or file content (which may not have identical content to the output
     # `lockfile_digest`).
@@ -225,7 +233,11 @@ async def load_lockfile(
 
     lockfile_contents = await get_digest_contents(lockfile_digest)
     lock_bytes = lockfile_contents[0].content
-    is_pex_native = is_probably_pex_json_lockfile(lock_bytes)
+    lockfile_format = (
+        LockfileFormat.Pex
+        if is_probably_pex_json_lockfile(lock_bytes)
+        else LockfileFormat.ConstraintsDeprecated
+    )
     constraints_strings = None
 
     metadata_url = PythonLockfileMetadata.metadata_location_for_lockfile(lockfile.url)
@@ -256,7 +268,7 @@ async def load_lockfile(
             pass
 
     if not metadata:
-        if is_pex_native:
+        if lockfile_format == LockfileFormat.Pex:
             header_delimiter = "//"
             stripped_lock_bytes = strip_comments_from_pex_json_lockfile(lock_bytes)
             lockfile_digest = await create_digest(
@@ -286,7 +298,7 @@ async def load_lockfile(
         lockfile_path,
         metadata,
         requirement_estimate,
-        is_pex_native,
+        lockfile_format,
         constraints_strings,
         original_lockfile=lockfile,
     )

src/python/pants/backend/python/util_rules/pex_test.py

@@ -47,6 +47,7 @@
     EntireLockfile,
     LoadedLockfile,
     Lockfile,
+    LockfileFormat,
     PexRequirements,
     Resolve,
     ResolvePexConfig,
@@ -703,7 +704,9 @@ def create_loaded_lockfile(is_pex_lock: bool) -> LoadedLockfile:
             lockfile_path,
             metadata=None,
             requirement_estimate=2,
-            is_pex_native=is_pex_lock,
+            lockfile_format=LockfileFormat.Pex
+            if is_pex_lock
+            else LockfileFormat.ConstraintsDeprecated,
             as_constraints_strings=None,
             original_lockfile=lockfile_obj,
         )

src/python/pants/core/goals/update_build_files_test.py

@@ -17,7 +17,11 @@
 from pants.backend.python.util_rules import pex
 from pants.backend.python.util_rules.interpreter_constraints import InterpreterConstraints
 from pants.backend.python.util_rules.lockfile_metadata import PythonLockfileMetadata
-from pants.backend.python.util_rules.pex_requirements import LoadedLockfile, Lockfile
+from pants.backend.python.util_rules.pex_requirements import (
+    LoadedLockfile,
+    Lockfile,
+    LockfileFormat,
+)
 from pants.core.goals.update_build_files import (
     FormatWithBlackRequest,
     FormatWithBuildifierRequest,
@@ -185,7 +189,7 @@ def assert_ics(
             "black.lock",
             metadata=metadata,
             requirement_estimate=1,
-            is_pex_native=True,
+            lockfile_format=LockfileFormat.Pex,
             as_constraints_strings=None,
             original_lockfile=Lockfile(
                 "black.lock", url_description_of_origin="foo", resolve_name="black"