Ensure the sandbox distdir exists when creating dists via PEP517 (Che…

…rrypick of #16647) (#16660)

Also fixes a docsite text alignment issue that didn't merit its own change.

docs/markdown/Python/python/python-distributions.md

@@ -180,8 +180,8 @@ For each `python_source` target S, the distribution in which S's code is publish
 1. A `python_distribution` that depends, directly or indirectly, on S.
 2. Is S's closest filesystem ancestor among those satisfying 1.
 
-If there are multiple such exported source files at the same degree of ancestry, the ownership  
-is ambiguous and an error is raised. If there is no `python_distribution` that depends on S  
+If there are multiple such exported source files at the same degree of ancestry, the ownership
+is ambiguous and an error is raised. If there is no `python_distribution` that depends on S
 and is its ancestor, then there is no owner and an error is raised.
 
 This algorithm implies that all source files published by a distribution must be below it in the filesystem. It also guarantees that a source file is only published by a single distribution.

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

@@ -144,6 +144,7 @@ class DistBuildResult:
 _BACKEND_SHIM_BOILERPLATE = """
 # DO NOT EDIT THIS FILE -- AUTOGENERATED BY PANTS
 
+import os
 import {build_backend_module}
 
 backend = {build_backend_object}
@@ -154,6 +155,7 @@ class DistBuildResult:
 wheel_config_settings = {wheel_config_settings_str}
 sdist_config_settings = {sdist_config_settings_str}
 
+os.makedirs(dist_dir, exist_ok=True)
 wheel_path = backend.build_wheel(dist_dir, wheel_config_settings) if build_wheel else None
 sdist_path = backend.build_sdist(dist_dir, sdist_config_settings) if build_sdist else None