CMake: Check that backend targets are defined
Create a generator expression that fails to evaluate if a backend does
not exist. This avoids confusing compilation errors.
Change-Id: I5475fa53bf604b6cc445d9774b96fd8d5eb66f09
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/44564
Commit-Queue: Wyatt Hepler <hepler@google.com>
Reviewed-by: Vic Yang <victoryang@google.com>
diff --git a/pw_build/docs.rst b/pw_build/docs.rst
index c974828..c2fe2f5 100644
--- a/pw_build/docs.rst
+++ b/pw_build/docs.rst
@@ -476,6 +476,18 @@
* Temporarily override a backend by setting it interactively with ``ccmake`` or
``cmake-gui``.
+If the backend is set to a build target that does not exist, there will be an
+error message like the following:
+
+.. code-block::
+
+ CMake Error at pw_build/pigweed.cmake:244 (add_custom_target):
+ Error evaluating generator expression:
+
+ $<TARGET_PROPERTY:my_backend_that_does_not_exist,TYPE>
+
+ Target "my_backend_that_does_not_exist" not found.
+
Toolchain setup
---------------
In CMake, the toolchain is configured by setting CMake variables, as described
diff --git a/pw_build/pigweed.cmake b/pw_build/pigweed.cmake
index a004cd4..37b0212 100644
--- a/pw_build/pigweed.cmake
+++ b/pw_build/pigweed.cmake
@@ -238,6 +238,14 @@
set("${NAME}_BACKEND" "${arg_DEFAULT_BACKEND}" CACHE STRING
"Backend for ${NAME}")
+ # This target is never used; it simply tests that the specified backend
+ # actually exists in the build. The generator expression will fail to evaluate
+ # if the target is not defined.
+ add_custom_target(_pw_check_that_backend_for_${NAME}_is_defined
+ COMMAND
+ ${CMAKE_COMMAND} -E echo "$<TARGET_PROPERTY:${${NAME}_BACKEND},TYPE>"
+ )
+
# Define the facade library, which is used by the backend to avoid circular
# dependencies.
add_library("${NAME}.facade" INTERFACE)
