platform_data implementation (#78)
* platform_data implementation
* update doc string for additional clarification
* update doc string
* move BUILD.bazel under experimental/platform_data
* add load statement to example
diff --git a/experimental/platform_data/BUILD.bazel b/experimental/platform_data/BUILD.bazel
new file mode 100644
index 0000000..94ececc
--- /dev/null
+++ b/experimental/platform_data/BUILD.bazel
@@ -0,0 +1,3 @@
+exports_files([
+ "defs.bzl",
+])
diff --git a/experimental/platform_data/defs.bzl b/experimental/platform_data/defs.bzl
new file mode 100644
index 0000000..0e739b0
--- /dev/null
+++ b/experimental/platform_data/defs.bzl
@@ -0,0 +1,85 @@
+"""
+The platform_data rule can be used to change the target platform of a target,
+and then depend on that elsewhere in the build tree. For example:
+load("@platforms//experimental/platform_data:defs.bzl", "platform_data")
+
+cc_binary(name = "foo")
+
+platform_data(
+ name = "foo_embedded",
+ target = ":foo",
+ platform = "//my/new:platform",
+)
+
+py_binary(
+ name = "flasher",
+ srcs = ...,
+ data = [
+ ":foo_embedded",
+ ],
+)
+
+Regardless of what platform the top-level :flasher binary is built for,
+the :foo_embedded target will be built for //my/new:platform.
+
+Note that if you depend on :foo_embedded it's not exactly the same as depending on :foo, since it won't forward all the same providers. In the future, we can extend this to add some common providers as needed."""
+
+def _target_platform_transition_impl(attr):
+ return {
+ "//command_line_option:platforms": str(attr.platform),
+ }
+
+_target_platform_transition = transition(
+ implementation = _target_platform_transition_impl,
+ inputs = [],
+ outputs = [
+ "//command_line_option:platforms",
+ ],
+)
+
+def _platform_data_impl(ctx):
+ target = ctx.attr.target
+
+ default_info = target[DefaultInfo]
+ files = default_info.files
+ original_executable = default_info.files_to_run.executable
+ runfiles = default_info.default_runfiles
+
+ new_executable = ctx.actions.declare_file(ctx.attr.name)
+
+ ctx.actions.symlink(
+ output = new_executable,
+ target_file = original_executable,
+ is_executable = True,
+ )
+
+ files = depset(direct = [new_executable], transitive = [files])
+ runfiles = runfiles.merge(ctx.runfiles([new_executable]))
+
+ return [
+ DefaultInfo(
+ files = files,
+ runfiles = runfiles,
+ executable = new_executable,
+ )
+ ]
+
+platform_data = rule(
+ implementation = _platform_data_impl,
+ attrs = {
+ "target": attr.label(
+ allow_files = False,
+ executable = True,
+ mandatory = True,
+ cfg = _target_platform_transition,
+ ),
+ "platform": attr.label(
+ mandatory = True,
+ ),
+ "_allowlist_function_transition": attr.label(
+ default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
+ ),
+ },
+ executable = True,
+)
+
