fix: Propagate testonly et al for wheel .dist targets (#1064)

* Propagate testonly et al for wheel `.dist` targets

The `.dist` target depends on the wheel, so it must copy the
`testonly` setting as well as some others.

* Also adds a utility function to do this, since the multi-version
  rules also do this copying.

Fixes #1057

* fixup! Allow building with unreleased Bazel versions. (#1063)

docs/BUILD.bazel

@@ -84,6 +84,7 @@ bzl_library(
         "//python/private:py_package.bzl",
         "//python/private:py_wheel.bzl",
         "//python/private:stamp.bzl",
+        "//python/private:util.bzl",
     ],
 )
 

examples/wheel/BUILD.bazel

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+load("@bazel_skylib//rules:build_test.bzl", "build_test")
 load("//examples/wheel/private:wheel_utils.bzl", "directory_writer")
 load("//python:defs.bzl", "py_library", "py_test")
 load("//python:packaging.bzl", "py_package", "py_wheel")
@@ -50,6 +51,7 @@ directory_writer(
 # Package just a specific py_libraries, without their dependencies
 py_wheel(
     name = "minimal_with_py_library",
+    testonly = True,  # Set this to verify the generated .dist target doesn't break things
     # Package data. We're building "example_minimal_library-0.0.1-py3-none-any.whl"
     distribution = "example_minimal_library",
     python_tag = "py3",
@@ -60,6 +62,11 @@ py_wheel(
     ],
 )
 
+build_test(
+    name = "dist_build_tests",
+    targets = [":minimal_with_py_library.dist"],
+)
+
 # Package just a specific py_libraries, without their dependencies
 py_wheel(
     name = "minimal_with_py_library_with_stamp",

python/packaging.bzl

@@ -16,6 +16,7 @@
 
 load("//python/private:py_package.bzl", "py_package_lib")
 load("//python/private:py_wheel.bzl", _PyWheelInfo = "PyWheelInfo", _py_wheel = "py_wheel")
+load("//python/private:util.bzl", "copy_propagating_kwargs")
 
 # Re-export as public API
 PyWheelInfo = _PyWheelInfo
@@ -148,6 +149,7 @@ def py_wheel(name, twine = None, **kwargs):
         name = _dist_target,
         wheel = name,
         out = kwargs.pop("dist_folder", "{}_dist".format(name)),
+        **copy_propagating_kwargs(kwargs)
     )
 
     _py_wheel(name = name, **kwargs)

python/private/BUILD.bazel

@@ -41,6 +41,7 @@ exports_files(
         "py_wheel.bzl",
         "reexports.bzl",
         "stamp.bzl",
+        "util.bzl",
     ],
     visibility = ["//docs:__pkg__"],
 )

python/private/util.bzl

@@ -0,0 +1,31 @@
+"""Functionality shared by multiple pieces of code."""
+
+def copy_propagating_kwargs(from_kwargs, into_kwargs = None):
+    """Copies args that must be compatible between two targets with a dependency relationship.
+
+    This is intended for when one target depends on another, so they must have
+    compatible settings such as `testonly` and `compatible_with`. This usually
+    happens when a macro generates multiple targets, some of which depend
+    on one another, so their settings must be compatible.
+
+    Args:
+        from_kwargs: keyword args dict whose common kwarg will be copied.
+        into_kwargs: optional keyword args dict that the values from `from_kwargs`
+            will be copied into. The values in this dict will take precedence
+            over the ones in `from_kwargs` (i.e., if this has `testonly` already
+            set, then it won't be overwritten).
+            NOTE: THIS WILL BE MODIFIED IN-PLACE.
+
+    Returns:
+        Keyword args to use for the depender target derived from the dependency
+        target. If `into_kwargs` was passed in, then that same object is
+        returned; this is to facilitate easy `**` expansion.
+    """
+    if into_kwargs == None:
+        into_kwargs = {}
+
+    # Include tags because people generally expect tags to propagate.
+    for attr in ("testonly", "tags", "compatible_with", "restricted_to"):
+        if attr in from_kwargs and attr not in into_kwargs:
+            into_kwargs[attr] = from_kwargs[attr]
+    return into_kwargs