Fix running python_sources with pex --executable (#21047)

This fixes the feature added in #20497 as it broke using `pants run` on
a python_source if the file name has `-` or other invalid characters.
Bug reported here:

https://pantsbuild.slack.com/archives/C046T6T9U/p1717624913138789?thread_ts=1717624913.138789&cid=C046T6T9U

The other integration test for the pex --executable feature only tested
running pex_binary, not python_source. So, I missed applying some of the
path logic to both cases.

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

@@ -57,7 +57,7 @@ def _executable_main(self) -> Optional[Executable]:
         if not all(part.isidentifier() for part in source_name.split(".")):
             # If the python source is not importable (python modules can't be named with '-'),
             # then it must be an executable script.
-            executable = Executable(self.source.value)
+            executable = Executable.create(self.address, self.source.value)
         else:
             # The module is importable, so entry_point will do the heavy lifting instead.
             executable = None

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

@@ -112,27 +112,37 @@ def run_run_request(
 
 
 @pytest.mark.parametrize(
-    "global_default_value, field_value, run_uses_sandbox",
+    "global_default_value, field_value, run_uses_sandbox, importable_script_name",
     [
         # Nothing set -> True
-        (None, None, True),
+        (None, None, True, True),
+        (None, None, True, False),
         # Field set -> use field value
-        (None, True, True),
-        (None, False, False),
+        (None, True, True, True),
+        (None, True, True, False),
+        (None, False, False, True),
+        (None, False, False, False),
         # Global default set -> use default
-        (True, None, True),
-        (False, None, False),
+        (True, None, True, True),
+        (True, None, True, False),
+        (False, None, False, True),
+        (False, None, False, False),
         # Both set -> use field
-        (True, True, True),
-        (True, False, False),
-        (False, True, True),
-        (False, False, False),
+        (True, True, True, True),
+        (True, True, True, False),
+        (True, False, False, True),
+        (True, False, False, False),
+        (False, True, True, True),
+        (False, True, True, False),
+        (False, False, False, True),
+        (False, False, False, False),
     ],
 )
 def test_run_sample_script(
     global_default_value: bool | None,
     field_value: bool | None,
     run_uses_sandbox: bool,
+    importable_script_name: bool,
     rule_runner: PythonRuleRunner,
 ) -> None:
     """Test that we properly run a `python_source` target.
@@ -141,9 +151,11 @@ def test_run_sample_script(
     - We can handle source roots.
     - We run in-repo when requested, and handle codegen correctly.
     - We propagate the error code.
+    - We can handle scripts without importable file name.
     """
+    script_name = "app.py" if importable_script_name else "my-executable.py"
     sources = {
-        "src_root1/project/app.py": dedent(
+        f"src_root1/project/{script_name}": dedent(
             """\
             import sys
             from utils.strutil import my_file
@@ -200,7 +212,7 @@ def my_file():
         ),
     ]
     rule_runner.set_options(args, env_inherit={"PATH", "PYENV_ROOT", "HOME"})
-    target = rule_runner.get_target(Address("src_root1/project", relative_file_path="app.py"))
+    target = rule_runner.get_target(Address("src_root1/project", relative_file_path=script_name))
     exit_code, stdout, stderr = run_run_request(rule_runner, target)
 
     assert "Hola, mundo.\n" in stderr

src/python/pants/backend/python/target_types.py

@@ -301,6 +301,12 @@ def spec(self) -> str:
 class Executable(MainSpecification):
     executable: str
 
+    @classmethod
+    def create(cls, address: Address, filename: str) -> Executable:
+        # spec_path is relative to the workspace. The rule is responsible for
+        # stripping the source root as needed.
+        return cls(os.path.join(address.spec_path, filename).lstrip(os.path.sep))
+
     def iter_pex_args(self) -> Iterator[str]:
         yield "--executable"
         # We do NOT yield self.executable or self.spec
@@ -409,9 +415,7 @@ def compute_value(cls, raw_value: Optional[str], address: Address) -> Optional[E
             return None
         if not isinstance(value, str):
             raise InvalidFieldTypeException(address, cls.alias, value, expected_type="a string")
-        # spec_path is relative to the workspace. The rule is responsible for
-        # stripping the source root as needed.
-        return Executable(os.path.join(address.spec_path, value).lstrip(os.path.sep))
+        return Executable.create(address, value)
 
 
 class PexArgsField(StringSequenceField):

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

@@ -12,6 +12,7 @@
 
 from pants.backend.python.subsystems.setup import PythonSetup
 from pants.backend.python.target_types import (
+    Executable,
     MainSpecification,
     PexLayout,
     PythonRequirementsField,
@@ -49,6 +50,7 @@
 from pants.engine.addresses import Address, Addresses
 from pants.engine.collection import DeduplicatedCollection
 from pants.engine.fs import Digest, DigestContents, GlobMatchErrorBehavior, MergeDigests, PathGlobs
+from pants.engine.internals.graph import Owners, OwnersRequest
 from pants.engine.rules import Get, MultiGet, collect_rules, rule
 from pants.engine.target import (
     Target,
@@ -554,6 +556,17 @@ async def create_pex_from_targets(
             await _warn_about_any_files_targets(
                 request.addresses, transitive_targets, union_membership
             )
+    elif isinstance(request.main, Executable):
+        # The source for an --executable main must be embedded in the pex even if request.include_source_files is False.
+        # If include_source_files is True, the executable source should be included in the (transitive) dependencies.
+        owners = await Get(
+            Owners,
+            OwnersRequest(
+                (request.main.spec,), owners_not_found_behavior=GlobMatchErrorBehavior.error
+            ),
+        )
+        owning_targets = await Get(Targets, Addresses(owners))
+        sources = await Get(PythonSourceFiles, PythonSourceFilesRequest(owning_targets))
     else:
         sources = PythonSourceFiles.empty()