Support .egg-info dist metadata.

This will allow inventorying system interpreters for use with both
resolving from them (and venvs) and thus supporting strict support
for `--provided` / `--exclude`.

The new `-d/--distributions` option is added to `pex3 interpreter
inspect` to support creating these inventories.

pex/build_system/pep_517.py

@@ -13,7 +13,7 @@
 from pex.build_system import DEFAULT_BUILD_BACKEND
 from pex.build_system.pep_518 import BuildSystem, load_build_system
 from pex.common import safe_mkdtemp
-from pex.dist_metadata import DistMetadata, Distribution
+from pex.dist_metadata import DistMetadata, Distribution, MetadataType
 from pex.jobs import Job, SpawnedJob
 from pex.pip.version import PipVersion, PipVersionValue
 from pex.resolve.resolvers import Resolver
@@ -24,7 +24,7 @@
 from pex.util import named_temporary_file
 
 if TYPE_CHECKING:
-    from typing import Any, Dict, Iterable, Mapping, Optional, Text, Tuple, Union
+    from typing import Any, Dict, Iterable, Mapping, Optional, Text, Union
 
 _DEFAULT_BUILD_SYSTEMS = {}  # type: Dict[PipVersionValue, BuildSystem]
 
@@ -272,4 +272,4 @@ def spawn_prepare_metadata(
             pip_version=pip_version,
         )
     )
-    return spawned_job.map(lambda _: DistMetadata.load(build_dir))
+    return spawned_job.map(lambda _: DistMetadata.load(build_dir, MetadataType.DIST_INFO))

pex/cli/commands/interpreter.py

@@ -8,6 +8,7 @@
 
 from pex.cli.command import BuildTimeCommand
 from pex.commands.command import JsonMixin, OutputMixin
+from pex.dist_metadata import find_distributions
 from pex.interpreter import PythonInterpreter
 from pex.interpreter_constraints import InterpreterConstraint
 from pex.resolve import target_options
@@ -61,6 +62,15 @@ def _add_inspect_arguments(cls, parser):
                 "and will contain the path to the interpreter."
             ),
         )
+        parser.add_argument(
+            "-d",
+            "--distributions",
+            action="store_true",
+            help=(
+                "Include information about the distributions installed on the interpreter's"
+                "`sys.path`."
+            ),
+        )
         cls.add_json_options(parser, entity="verbose output")
 
         interpreter_options_parser = parser.add_argument_group(
@@ -125,6 +135,7 @@ def _inspect(self):
                         interpreter_info.update(
                             version=interpreter.identity.version_str,
                             requirement=str(InterpreterConstraint.exact_version(interpreter)),
+                            sys_path=interpreter.sys_path,
                             platform=str(interpreter.platform),
                             venv=interpreter.is_venv,
                         )
@@ -151,6 +162,18 @@ def _inspect(self):
                         interpreter_info[
                             "marker_environment"
                         ] = interpreter.identity.env_markers.as_dict()
+                    if self.options.distributions:
+                        interpreter_info["distributions"] = {
+                            dist.project_name: {
+                                "version": dist.version,
+                                "location": dist.location,
+                                "requires_python": str(dist.metadata.requires_python),
+                                "requires_dists": [
+                                    str(req) for req in dist.metadata.requires_dists
+                                ],
+                            }
+                            for dist in find_distributions(search_path=interpreter.sys_path)
+                        }
                     self.dump_json(self.options, interpreter_info, out)
                 else:
                     out.write(interpreter.binary)