pw_function: Dynamic allocation for upstream host

Enable dynamic allocation in pw_function, for Bazel upstream host builds only. This has no effect on downstream projects or non-host builds. Change-Id: Ife7eef3e13e533867c923c5c2dc9dd966f637ceb Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/221871 Reviewed-by: Erik Gilling <[email protected]> Commit-Queue: Rob Mohr <[email protected]> Lint: Lint 🤖 <[email protected]> Reviewed-by: Taylor Cramer <[email protected]> Commit-Queue: Ted Pudlik <[email protected]>
google · Jul 11, 2024 · cd7e34b · cd7e34b
1 parent 61c6b9a
commit cd7e34b
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diff --git a/.bazelrc b/.bazelrc
@@ -128,6 +128,7 @@ common --@stm32f4xx_hal_driver//:cmsis_init=@cmsis_device_f4//:default_cmsis_ini
 
 common --//pw_env_setup/py:pigweed_json=//:pigweed.json
 
+build --//pw_function:config_override=//pw_function:upstream_default_config
 
 # Config for the rp2040 platform.
 #

diff --git a/pw_function/BUILD.bazel b/pw_function/BUILD.bazel
@@ -12,6 +12,7 @@
 # License for the specific language governing permissions and limitations under
 # the License.
 
+load("@bazel_skylib//lib:selects.bzl", "selects")
 load(
  "//pw_build:pigweed.bzl",
  "pw_cc_test",
@@ -84,3 +85,29 @@ pw_cc_test(
  ":scope_guard",
  ],
 )
+
+# pw_function config for upstream builds.
+#
+# See https://pigweed.dev/pw_function/#dynamic-allocation for more context.
+alias(
+ name = "upstream_default_config",
+ actual = selects.with_or({
+ (
+ "@platforms//os:android",
+ "@platforms//os:chromiumos",
+ "@platforms//os:linux",
+ "@platforms//os:macos",
+ "@platforms//os:windows",
+ ): ":config_for_host",
+ "//conditions:default": "//pw_build:default_module_config",
+ }),
+ visibility = ["//visibility:private"],
+)
+
+cc_library(
+ name = "config_for_host",
+ defines = [
+ "PW_FUNCTION_ENABLE_DYNAMIC_ALLOCATION=1",
+ ],
+ visibility = ["//visibility:private"],
+)
diff --git a/pw_function/docs.rst b/pw_function/docs.rst
@@ -357,6 +357,15 @@ enabled but a compile-time check for the inlining is still required,
  cast from :cpp:type:`pw::InlineFunction` to a regular
  :cpp:type:`pw::Function` will **ALWAYS** allocate memory.
 
+.. note::
+
+ When building Pigweed itself for host platforms, we enable dynamic
+ allocation. This is required for some modules that use ``pw::Function``,
+ like :ref:`module-pw_bluetooth_sapphire`. But it is *not* the default for
+ downstream projects because it introduces a difference between host and
+ non-host builds. This difference has the potential to cause breakages if
+ code is built for host first, and then later ported to device.
+
 Invoking ``pw::Function`` from a C-style API
 ============================================
 .. _trampoline layers: https://en.wikipedia.org/wiki/Trampoline_(computing)