feat: allow an optional platform definition for container arch

Author: Allan Clark

docker_compose_test/docker_compose_test.bzl

@@ -17,6 +17,7 @@ load("@rules_pkg//:pkg.bzl", "pkg_tar")
 load("@repo_absolute_path//:build_root.bzl",  "BUILD_WORKSPACE_DIRECTORY")
 load("@rules_go//go:def.bzl", "go_test")
 load("@rules_oci//oci:defs.bzl", "oci_image", "oci_load")
+load(":multi_platform.bzl", "multi_platform")
 
 common_tags = [
     "docker", # these tests depend on docker
@@ -63,6 +64,7 @@ def go_docker_compose_test(
     data = [],
     tags = [],
     size = "large",
+    platforms = None,
     **kwargs,
 ):
     tags = common_tags + tags
@@ -79,8 +81,12 @@ def go_docker_compose_test(
         tags = tags + go_test_target_tags,
         testonly = True,
     )
+    if platforms:
+        multi_platform(name = name + ".go__test", actual = name + ".go_test", platforms = platforms, testonly = True)
+    else:
+        native.alias(name = name + ".go__test", actual = name + ".go_test", testonly = True)
 
-    compiled_tests_target = ":" + name + ".go_test"
+    compiled_tests_target = ":" + name + ".go__test"
 
     pkg_tar(
         name = name + ".compiled_go_test_target",

docker_compose_test/multi_platform.bzl

@@ -0,0 +1,36 @@
+"a rule transitioning an oci_image to multiple platforms"
+# based (Apache-2.0) on rules_oci/examples/transition.bzl
+
+
+def _multiplatform_transition(settings, attr):
+    """this function simply returns a string-list of the platforms as a transition."""
+    return [
+        {"//command_line_option:platforms": str(platform)}
+        for platform in attr.platforms
+    ]
+
+multiplatform_transition = transition(
+    # outputs a transition as a list of platforms as defined in the calling rule; these will cause
+    # the referencing rule to split its definition based in iterations of the selected platforms as
+    # thought given as a command-line argument
+
+    implementation = _multiplatform_transition,
+    inputs = [],
+    outputs = ["//command_line_option:platforms"],
+)
+
+def _impl(ctx):
+    """this function mostly acts as an alias() rule but splits across combinations of 'platforms'"""
+    return DefaultInfo(files = depset(ctx.files.actual))
+
+multi_platform = rule(
+    doc = "causes the rule chain of dependencies to be split across values of 'platforms' and replacing the default value (based on the host)",
+    implementation = _impl,
+    attrs = {
+        "actual": attr.label(cfg = multiplatform_transition),
+        "platforms": attr.label_list(),
+        "_allowlist_function_transition": attr.label(
+            default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
+        ),
+    },
+)

examples/go-test-image-test-with-platforms/BUILD.bazel

@@ -0,0 +1,55 @@
+# Copyright (c) 2024, Salesforce, Inc.
+# SPDX-License-Identifier: Apache-2
+
+# 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.
+
+load("@rules_docker_compose_test//docker_compose_test:docker_compose_test.bzl", "go_docker_compose_test")
+
+# As compared to examples/go-test-image-test, this example will succeed on non-linux hosts that run
+# linux-archutecture containers (ie Mac "darwin")
+#
+# This example will compile linux unittests on a non-linux host, build a multi-arch OCI image,and
+# use docker-compose to turn up the appropriate container to execute the corresponding architecture
+# of compiled go testcase.
+#
+# We effectively overrule the default assumption that platform == host platform by providing two
+# choices in a transition defined in multi_platform.bzl which causes the targets to duplicate
+# across platform values and align corresponding platform values.
+# 
+# We do this by:
+# 1. providing a list of platforms to iterate
+# 2. iterating that list in a transition around the `go_test()` target
+#
+# the same `cd examples && bazel test //go-test-image-test-with-platforms` demonstrates
+
+ARCH=["arm64", "x86_64"]
+
+[platform(
+    name = "linux_{}".format(a),
+    constraint_values = [
+        "@platforms//os:linux",  # yes, Mac docker runs linux images
+        "@platforms//cpu:{}".format(a),
+    ],
+) for a in ARCH ]
+
+# The following go_docker_compose_test adds a "platforms" attribute, and pathname-based changes:
+
+go_docker_compose_test(
+    name = "go-test-image-test-with-platforms",
+    docker_compose_file = ":docker-compose.yml",
+    docker_compose_test_container = "test_container",  # container name is subdir:test_container
+    platforms = [ "linux_{}".format(a) for a in ARCH ],  # override default platform==host asusmption
+    test_srcs = [ "example_test.go", "another_test.go" ],
+    test_deps = [],
+    test_image_base = "@ubuntu",
+)

examples/go-test-image-test-with-platforms/another_test.go

@@ -0,0 +1,8 @@
+package main
+
+import "testing"
+
+// identical to //examples/go-test-image-test/another_test.go
+func TestExample2(t *testing.T) {
+	  t.Log("bar")
+}

examples/go-test-image-test-with-platforms/docker-compose.yml

@@ -0,0 +1,22 @@
+# Copyright (c) 2024, Salesforce, Inc.
+# SPDX-License-Identifier: Apache-2
+
+# 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.
+
+services:
+  # service name matches <docker_compose_test_container>
+  test_container:
+    # image is <subdir>:<docker_compose_test_container>
+    image: go-test-image-test-with-platforms:test_container
+    # test binary is /tests/<target_name>.go_test
+    entrypoint: ["tests/go-test-image-test-with-platforms.go_test"]

examples/go-test-image-test-with-platforms/example_test.go

@@ -0,0 +1,8 @@
+package main
+
+import "testing"
+
+// identical to //examples/go-test-image-test/example_test.go
+func TestExample(t *testing.T) {
+	  t.Log("foo")
+}