PSA: FIDL "_hlcpp" suffix will be required in GN

[Mitchell Kember]

You can stop reading if you don’t use FIDL HLCPP bindings in the Fuchsia GN build.

In the past, depending on a FIDL target gave you HLCPP bindings by default. Soon, you will be required to explicitly choose the bindings flavor using the “_hlcpp” or “_cpp” suffix. For example:

executable("foo") {   # ...   deps = [     # DEPRECATED: Implicitly choose HLCPP.     "//sdk/fidl/fuchsia.component",     # Explicitly choose HLCPP with "_hlcpp".     "//sdk/fidl/fuchsia.component:fuchsia.component_hlcpp",     # Explicitly choose the new C++ bindings with "_cpp".     "//sdk/fidl/fuchsia.component:fuchsia.component_cpp",   ] }

See Comparing C, new C++, and high-level C++ language bindings for help deciding which C++ bindings you should use.

This is tracked by fxbug.dev/108354, and enforcement starts with an allowlist in fxrev.dev/718410. I will migrate all existing build targets in the coming days. After the migration, if you try using the old way, you’ll get a GN error like this:

ERROR at //build/config/BUILDCONFIG.gn:2006:3: Dependency not allowed.   target(target_type, target_name) {   ^--------------------------------- The item //examples/fidl/hlcpp/unittests:example-cpp-host-test_executable can not depend on //examples/fidl/fuchsia.examples:fuchsia.examples because it is not in //examples/fidl/fuchsia.examples:fuchsia.examples's visibility list: [   //sdk/*   //src/*   //third_party/*   //tools/*   //vendor/*   //zircon/* ]

Please reach out if you have any questions.

Mitchell

[Fabrice de Gans]

Will this be applied to the GN SDK or is it only in-tree?

Thank you,

Fabrice

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[Mitchell Kember]

On Thu, Sep 1, 2022 at 11:01 AM Fabrice de Gans <fde...@google.com> wrote:

Will this be applied to the GN SDK or is it only in-tree?

No changes to the GN SDK, which only supports HLCPP right now. This change only applies to repos that use fuchsia.git's //build/fidl.gni.