Support source-less wheels with dependencies

`rules_python` `2.3.x` wraps source-less wheels in a `py_library`
whose `srcs` target has no Python files. Forward the target only when
it has valid sources, and cover the wrapper behavior with unit tests.

Author: hartikainen

news/sourceless-wheel-srcs.fixed.md

@@ -0,0 +1,2 @@
+(pypi) Fixed analysis failures for source-less wheels with dependencies in
+per-wheel repositories.

python/private/pypi/whl_library_targets.bzl

@@ -101,7 +101,7 @@ def whl_library_targets(
         **kwargs: Extra args passed to the {obj}`whl_library_deps_targets` and {obj}`whl_library_srcs`.
     """
     create_extra_targets = bool(requires_dist or group_name) and dep_template
-    whl_library_srcs(
+    wrapper_srcs = whl_library_srcs(
         name = name,
         sdist_filename = sdist_filename,
         data_exclude = data_exclude,
@@ -133,6 +133,7 @@ def whl_library_targets(
             dep_template = dep_template,  # only needed if requires_dist is present
             repo = None,  # set aliases in the same repo
             aliases = {},
+            srcs = wrapper_srcs,
             **kwargs
         )
 
@@ -193,9 +194,14 @@ def whl_library_srcs(
         pkg_name: {type}`str` The label name to use for the py_library target.
         native: {type}`native` The native struct for overriding in tests.
         rules: {type}`struct` A struct with references to rules for creating targets.
+
+    Returns:
+        The source labels attached to the generated `py_library`, or `None` when
+        `rules` does not define `py_library`.
     """
     tags = sorted(tags)
     data = [] + data
+    wrapper_srcs = None
 
     bins_for_data_label = []
 
@@ -301,6 +307,7 @@ def whl_library_srcs(
             # pure-Python code, e.g. pymssql, which is written in Cython.
             allow_empty = True,
         )
+        wrapper_srcs = [pkg_name] if srcs else []
 
         # NOTE: pyi files should probably be excluded because they're carried
         # by the pyi_srcs attribute. However, historical behavior included
@@ -328,13 +335,19 @@ def whl_library_srcs(
         )
 
         if not enable_implicit_namespace_pkgs:
+            generated_namespace_package_files = rules.create_inits(
+                srcs = srcs + data + pyi_srcs,
+                ignored_dirnames = [],  # If you need to ignore certain folders, you can patch rules_python here to do so.
+                root = "site-packages",
+            )
+            if not wrapper_srcs and generated_namespace_package_files:
+                wrapper_srcs = select({
+                    _IS_VENV_SITE_PACKAGES_YES: [],
+                    "//conditions:default": [pkg_name],
+                })
             generated_namespace_package_files = select({
                 _IS_VENV_SITE_PACKAGES_YES: [],
-                "//conditions:default": rules.create_inits(
-                    srcs = srcs + data + pyi_srcs,
-                    ignored_dirnames = [],  # If you need to ignore certain folders, you can patch rules_python here to do so.
-                    root = "site-packages",
-                ),
+                "//conditions:default": generated_namespace_package_files,
             })
             namespace_package_files += generated_namespace_package_files
             srcs = srcs + generated_namespace_package_files
@@ -356,6 +369,7 @@ def whl_library_srcs(
             experimental_venvs_site_packages = _VENV_SITE_PACKAGES_FLAG,
             namespace_package_files = namespace_package_files,
         )
+    return wrapper_srcs
 
 def whl_library_deps_targets(
         *,
@@ -369,6 +383,7 @@ def whl_library_deps_targets(
         group_deps = [],
         group_name = None,
         dep_template,
+        srcs = None,
         tags = [],
         visibility = ["//visibility:public"],
         native = native,
@@ -396,6 +411,9 @@ def whl_library_deps_targets(
         include: {type}`list[str]` The list of packages to include.
         group_name: {type}`str | None` name of the dependency group (if any).
         dep_template: {type}`str | None` The dep_template to use.
+        srcs: {type}`list[Label] | None` or a configurable expression with the
+            source labels attached to the wrapper `py_library`. If `None`, the
+            source library target is used.
         tags: {type}`list[str]` The tags set on the targets.
         repo: {type}`str | Label | None` The BUILD.bazel label to the parent repo that has the
             sources. If none, then will take the targets from the current dir.
@@ -501,10 +519,13 @@ def whl_library_deps_targets(
         )
 
     if hasattr(rules, "py_library"):
+        if srcs == None:
+            srcs = [repo_label(PY_SRCS_LABEL)]
         rules.py_library(
             name = py_library_label,
-            # We include as srcs to ensure that the (locations :pkg) works as expected.
-            srcs = [repo_label(PY_SRCS_LABEL)],
+            # Forward source-producing targets through `srcs` so downstream
+            # `$(locations :pkg)` expansion does not reject source-less wheels.
+            srcs = srcs,
             deps = _deps(
                 # We include as deps, so that `PyInfo` and friends (e.g. `pyi_srcs`) get
                 # propagated. Just passing the target as `srcs` is not enough to propagate

tests/pypi/whl_library_targets/whl_library_targets_tests.bzl

@@ -19,11 +19,46 @@ load(
     "//python/private/pypi:whl_library_targets.bzl",
     "whl_library_deps_targets",
     "whl_library_srcs",
+    "whl_library_targets",
 )  # buildifier: disable=bzl-visibility
 load("//tests/support/mocks:mocks.bzl", "mocks")
 
 _tests = []
 
+def _make_whl_library_targets_py_library_calls(
+        *,
+        srcs,
+        data,
+        generated_inits,
+        enable_implicit_namespace_pkgs = False):
+    py_library_calls = []
+    m_glob = mocks.glob()
+    m_glob.results.append([])  # bin
+    m_glob.results.append([])  # rewrite-bin
+    m_glob.results.append([])  # rewrite-record
+    m_glob.results.append(srcs)
+    m_glob.results.append(data)
+    m_glob.results.append([])  # pyi
+
+    whl_library_targets(
+        name = "foo-0-py3-none-any.whl",
+        metadata_name = "Foo",
+        requires_dist = ["bar"],
+        dep_template = "@pypi//{name}:{target}",
+        enable_implicit_namespace_pkgs = enable_implicit_namespace_pkgs,
+        filegroups = {},
+        native = struct(glob = m_glob.glob),
+        rules = struct(
+            create_inits = lambda **_: generated_inits,
+            env_marker_setting = lambda **_: None,
+            gen_wheel_record = lambda **_: None,
+            py_library = lambda **kwargs: py_library_calls.append(kwargs),
+            venv_rewrite_shebang = lambda **_: None,
+        ),
+    )
+
+    return py_library_calls
+
 def _test_filegroups(env):
     calls = []
 
@@ -191,6 +226,87 @@ def _test_whl_library_deps_targets(env):
 
 _tests.append(_test_whl_library_deps_targets)
 
+def _test_whl_library_targets_sourceless(env):
+    for enable_implicit_namespace_pkgs, expected_leaf_srcs in [
+        (False, [] + select({
+            Label("//python/config_settings:_is_venvs_site_packages_yes"): [],
+            "//conditions:default": [],
+        })),
+        (True, []),
+    ]:
+        py_library_calls = _make_whl_library_targets_py_library_calls(
+            srcs = [],
+            data = [],
+            generated_inits = [],
+            enable_implicit_namespace_pkgs = enable_implicit_namespace_pkgs,
+        )
+
+        env.expect.that_collection(py_library_calls).has_size(2)
+        if len(py_library_calls) != 2:
+            return
+
+        env.expect.that_dict(py_library_calls[0]).contains_at_least({
+            "srcs": expected_leaf_srcs,
+        })
+        env.expect.that_dict(py_library_calls[1]).contains_exactly({
+            "name": "pkg",
+            "srcs": [],
+            "deps": ["srcs", "@pypi//bar:pkg"],
+            "tags": [],
+            "visibility": ["//visibility:public"],
+        })  # buildifier: @unsorted-dict-items
+
+_tests.append(_test_whl_library_targets_sourceless)
+
+def _test_whl_library_targets_sourceful(env):
+    for srcs, data, generated_inits, expected_leaf_srcs, expected_wrapper_srcs in [
+        (
+            ["site-packages/foo.py"],
+            [],
+            [],
+            ["site-packages/foo.py"] + select({
+                Label("//python/config_settings:_is_venvs_site_packages_yes"): [],
+                "//conditions:default": [],
+            }),
+            ["srcs"],
+        ),
+        (
+            [],
+            ["site-packages/ext/mod.so"],
+            ["site-packages/ext/__init__.py"],
+            [] + select({
+                Label("//python/config_settings:_is_venvs_site_packages_yes"): [],
+                "//conditions:default": ["site-packages/ext/__init__.py"],
+            }),
+            select({
+                Label("//python/config_settings:_is_venvs_site_packages_yes"): [],
+                "//conditions:default": ["srcs"],
+            }),
+        ),
+    ]:
+        py_library_calls = _make_whl_library_targets_py_library_calls(
+            srcs = srcs,
+            data = data,
+            generated_inits = generated_inits,
+        )
+
+        env.expect.that_collection(py_library_calls).has_size(2)
+        if len(py_library_calls) != 2:
+            return
+
+        env.expect.that_dict(py_library_calls[0]).contains_at_least({
+            "srcs": expected_leaf_srcs,
+        })
+        env.expect.that_dict(py_library_calls[1]).contains_exactly({
+            "name": "pkg",
+            "srcs": expected_wrapper_srcs,
+            "deps": ["srcs", "@pypi//bar:pkg"],
+            "tags": [],
+            "visibility": ["//visibility:public"],
+        })  # buildifier: @unsorted-dict-items
+
+_tests.append(_test_whl_library_targets_sourceful)
+
 def _test_whl_library_deps_targets_no_deps(env):
     alias_calls = []
     filegroup_calls = []