Add pkgfilegroup for package-independent destination mappings (#128)

* Add pkgfilegroup for package-independent destination mappings

This adds an experimental rule, `pkgfilegroup`, along with associated Providers,
that gives rule developers and users a consistent mechanism for using the output
of bazel targets in packaging rules.

Inspired by #36.

Other capabilities that are provided by this that were not mentioned in #36 are:

- Creation of empty directories (`pkg_mkdirs`)
- Exclusion of files from a `pkgfilegroup` (`excludes`)
- Renames of files in a `pkgfilegroup` (`renames`)

* Add analysis tests for pkgfilegroup and friends

This provides some analysis tests for various features of `pkgfilegroup` and
`pkg_mkdirs`.  See #128.

You can run them by invoking `bazel test experimental/...` from the `pkg`
directory

This implementation of pkgfilegroup was inspired by #36.

pkg/.bazelignore

@@ -0,0 +1 @@
+tests/external_project

pkg/BUILD

@@ -89,3 +89,12 @@ py_library(
     srcs_version = "PY2AND3",
     visibility = ["//visibility:public"],
 )
+
+# Used within experimental/tests/ for external repo genpkg tests
+filegroup(
+    name = "loremipsum_txt",
+    srcs = [
+        "testdata/loremipsum.txt",
+    ],
+    visibility = ["//visibility:public"],
+)

pkg/WORKSPACE

@@ -1,4 +1,28 @@
+# Copyright 2020 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
 workspace(name = "rules_pkg")
 
 load("//:deps.bzl", "rules_pkg_dependencies")
+
 rules_pkg_dependencies()
+
+load("@bazel_skylib//:workspace.bzl", "bazel_skylib_workspace")
+
+bazel_skylib_workspace()
+
+local_repository(
+    name = "experimental_test_external_repo",
+    path = "experimental/tests/external_repo",
+)

pkg/deps.bzl

@@ -1,11 +1,34 @@
+# Copyright 2020 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
 # Workspace dependencies for rules_pkg/pkg
 
-# @federation: BEGIN @rules_pkg
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
 
+# @federation: BEGIN @rules_pkg
 
 def rules_pkg_dependencies():
-    pass
-
+    maybe(
+        http_archive,
+        name = "bazel_skylib",
+        urls = [
+            "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/1.0.2/bazel-skylib-1.0.2.tar.gz",
+            "https://github.com/bazelbuild/bazel-skylib/releases/download/1.0.2/bazel-skylib-1.0.2.tar.gz",
+        ],
+        sha256 = "97e70364e9249702246c0e9444bccdc4b847bed1eb03c5a3ece4f83dfe6abc44",
+    )
 
 def rules_pkg_register_toolchains():
     pass

pkg/experimental/BUILD

@@ -0,0 +1,18 @@
+# Copyright 2020 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+exports_files(
+    glob(["*.bzl"]),
+    visibility = ["//visibility:public"],
+)