Fix default layout and use of PEX-repositories for legacy lockfiles (p…

…antsbuild#15014)

As reported in pantsbuild#14980 and pantsbuild#14991: 1) the default layout of non-internal PEXes changed to `PACKED`, and 2) the PEX-repository subsetting optimization was disabled for manual or poetry lockfiles.

This change fixes those issues, and adds a test of the `pex_from_targets` codepath which decides which resolution strategy to use. But it also fairly significantly refactors the `PexRequest` consumption code to improve typesafety. In particular:
* Replaces the `is_all_constraints_resolve` special case with explicitly specified `PexLayout`s for those `PexRequests` (which would have been harder at the time when the special case was originally added, since `PexRequest.layout` didn't exist yet).
* Moves lockfile header parsing and PEX-native-detection into a `@rule` which produces a `LoadedLockfile`.
* Moves "subsetting of a lockfile or a repository PEX" to the `PexRequirements.from_subset` field, which takes a `LoadedLockfile` and asserts (not worth introducing another type yet probably) that the lockfile is PEX-native.
* Move the requirements which used to be attached to the `Lockfile`/`LockfileContents` off onto an `PexRequest.requirements = EntireLockfile` case, to assert that they are optional, and only used for metadata validation (rather than subsetting).

Fixes pantsbuild#14980 and fixes pantsbuild#14991.
# Rust tests and lints will be skipped. Delete if not intended.
[ci skip-rust]

# Building wheels and fs_util will be skipped. Delete if not intended.
[ci skip-build-wheels]

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

@@ -10,6 +10,7 @@
 from pants.backend.python.util_rules.interpreter_constraints import InterpreterConstraints
 from pants.backend.python.util_rules.pex import PexRequest
 from pants.backend.python.util_rules.pex_requirements import (
+    EntireLockfile,
     PexRequirements,
     ToolCustomLockfile,
     ToolDefaultLockfile,
@@ -21,7 +22,6 @@
 from pants.option.option_types import StrListOption, StrOption
 from pants.option.subsystem import Subsystem
 from pants.util.docutil import bin_name, doc_url
-from pants.util.ordered_set import FrozenOrderedSet
 
 
 class PythonToolRequirementsBase(Subsystem):
@@ -125,7 +125,7 @@ def pex_requirements(
         self,
         *,
         extra_requirements: Iterable[str] = (),
-    ) -> PexRequirements | ToolDefaultLockfile | ToolCustomLockfile:
+    ) -> PexRequirements | EntireLockfile:
         """The requirements to be used when installing the tool.
 
         If the tool supports lockfiles, the returned type will install from the lockfile rather than
@@ -139,28 +139,29 @@ def pex_requirements(
 
         hex_digest = calculate_invalidation_digest(requirements)
 
+        lockfile: ToolDefaultLockfile | ToolCustomLockfile
         if self.lockfile == DEFAULT_TOOL_LOCKFILE:
             assert self.default_lockfile_resource is not None
-            return ToolDefaultLockfile(
+            lockfile = ToolDefaultLockfile(
                 file_content=FileContent(
                     f"{self.options_scope}_default.lock",
                     importlib.resources.read_binary(*self.default_lockfile_resource),
                 ),
                 lockfile_hex_digest=hex_digest,
-                req_strings=FrozenOrderedSet(requirements),
                 resolve_name=self.options_scope,
                 uses_project_interpreter_constraints=(not self.register_interpreter_constraints),
                 uses_source_plugins=self.uses_requirements_from_source_plugins,
             )
-        return ToolCustomLockfile(
-            file_path=self.lockfile,
-            file_path_description_of_origin=f"the option `[{self.options_scope}].lockfile`",
-            lockfile_hex_digest=hex_digest,
-            req_strings=FrozenOrderedSet(requirements),
-            resolve_name=self.options_scope,
-            uses_project_interpreter_constraints=(not self.register_interpreter_constraints),
-            uses_source_plugins=self.uses_requirements_from_source_plugins,
-        )
+        else:
+            lockfile = ToolCustomLockfile(
+                file_path=self.lockfile,
+                file_path_description_of_origin=f"the option `[{self.options_scope}].lockfile`",
+                lockfile_hex_digest=hex_digest,
+                resolve_name=self.options_scope,
+                uses_project_interpreter_constraints=(not self.register_interpreter_constraints),
+                uses_source_plugins=self.uses_requirements_from_source_plugins,
+            )
+        return EntireLockfile(lockfile, complete_req_strings=tuple(requirements))
 
     @property
     def lockfile(self) -> str:

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

@@ -16,11 +16,7 @@
 from pants.backend.python.util_rules.interpreter_constraints import InterpreterConstraints
 from pants.backend.python.util_rules.pex import PexRequest, VenvPex, VenvPexProcess
 from pants.backend.python.util_rules.pex import rules as pex_rules
-from pants.backend.python.util_rules.pex_requirements import (
-    Lockfile,
-    LockfileContent,
-    PexRequirements,
-)
+from pants.backend.python.util_rules.pex_requirements import EntireLockfile, PexRequirements
 from pants.base.glob_match_error_behavior import GlobMatchErrorBehavior
 from pants.engine.fs import (
     CreateDigest,
@@ -62,7 +58,7 @@ class BuildSystemRequest:
 class BuildSystem:
     """A PEP 517/518 build system configuration."""
 
-    requires: PexRequirements | Lockfile | LockfileContent
+    requires: PexRequirements | EntireLockfile
     build_backend: str
 
     @classmethod