commit 886717437a55489898c03c89e69186a5efb877aa
author Taylor Cramer <cramertj@google.com> Tue Jun 13 19:52:37 2023 +0000
committer CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com> Tue Jun 13 19:52:37 2023 +0000
tree 984d6cd7c0d015fd0f7d53036802b4f1cbe5fa4d
parent 734cbf0a461a30fb1631c4a14b8a11737716a3d2

pw_build: Add `enable_if` to missing backend error

A dependency on a facade in a toolchain with a missing backend commonly
occurs by depending on the facade in a test. This change suggests using
`enable_if` to enable the test only when a backend is provided.

Tested: removed an existing `enable_if` and saw this error:

ERR Build error for //pw_chrono:system_clock.NO_BACKEND_SET(//targets/stm32f429i_disc1:stm32f429i_disc1_debug):
ERR
ERR   Attempted to build the //pw_chrono:system_clock facade with no backend.
ERR
ERR   If you are using this facade, ensure you have configured a backend
ERR   properly. The build arg for the facade must be set to a valid
ERR   backend in the toolchain. For example, you may need to add a line
ERR   like the following to the toolchain's .gni file:
ERR
ERR     pw_chrono_<FACADE_NAME>_BACKEND = "//path/to/the:backend"
ERR
ERR   Alternatively, if the target depending on this facade is a
<wrapped> `pw_test`
ERR   which should only be built in toolchains with a provided backend,
ERR   consider adding an `enable_if` to the dependent target:
ERR
ERR     pw_test(...) {
ERR       enable_if = pw_chrono_<FACADE_NAME>_BACKEND != ""
ERR       ...
ERR     }
ERR
ERR   If you are NOT using this facade, this error may have been
<wrapped> triggered
ERR   by trying to build all targets.
ERR
ERR Dependency path to this target:
ERR
ERR   gn path out //:default "//pw_chrono:system_clock.NO_BACKEND_SET(//targets/stm32f429i_disc1:stm32f429i_disc1_debug)"

Change-Id: I57324a88afa65528a230840cb939c15236a21703
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/151651
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Taylor Cramer <cramertj@google.com>
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>