Fuchsia

"fuchsia.images2" is marked sdk_category = "internal". Neither of it's library fuchsia.images2; declarations specifies @available.

This is mostly fine since internal libraries are not exposed. This can be observed by its absence in https://cs.opensource.google/fuchsia/fuchsia/+/main:sdk/history/13/. This also appears to be consistent with https://fxrev.dev/863858.

However, when building the SDK libraries (at an API level other than HEAD), these libraries are built at all API levels because there is no @available(added=HEAD) to prevent this.

To reproduce:

fx set minimal.x64 --args=override_target_api_level=11
fx build sdk:core
# Or a narrower target:
fx build x64-shared/obj/zircon/system/ulib/image-format/libimage-format.image_format.cc.o

The result is as follows:

[1/22](0) FIDLC //sdk/fidl/fuchsia.images2:fuchsia.images2_compile_fidlc(//build/fidl:fidling)
FAILED: fidling/gen/sdk/fidl/fuchsia.images2/fuchsia.images2/c/fuchsia.images2.fidl.tables.c fidling/gen/sdk/fidl/fuchsia.images2/fuchsia.images2.fidl.json 
../../prebuilt/third_party/python3/linux-x64/bin/python3 -S ../../build/rbe/output_leak_scanner.py --label //sdk/fidl/fuchsia.images2:fuchsia.images2_compile_fidlc\(//build/fidl:fidling\) fidling/gen/sdk/fidl/fuchsia.images2/fuchsia.images2/c/fuchsia.images2.fidl.tables.c fidling/gen/sdk/fidl/fuchsia.images2/fuchsia.images2.fidl.json -- ../../build/gn_run_binary.sh ../../prebuilt/third_party/clang/linux-x64/bin host_x64/fidlc @fidling/gen/sdk/fidl/fuchsia.images2/fuchsia.images2_compile_fidlc.args
../../sdk/fidl/fuchsia.images2/image_format.fidl:98:21: error: cannot find 'RectU' in library 'fuchsia.math' [https://fuchsia.dev/error/fi-0052]
    6: display_rect fuchsia.math.RectU;
                    ^~~~~~~~~~~~~~~~~~

The cause is that fuchsia.images2 is built at all API levels but fuchsia.math.RectU is only available at HEAD. This specific instance is easily fixable, but I think building fuchsia.images2 in this case is incorrect. That is also fixable, but we may want to reconsider the exclusion of internal SDKs from the requirements in https://fxrev.dev/863858.