commit 4f238babeb357b7739992449f1212a94ee1afa89
author Austin Foxley <afoxley@google.com> Mon May 06 23:02:45 2024 +0000
committer CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com> Mon May 06 23:02:45 2024 +0000
tree 178d983afe4cc4a9cd1ce76b2ea38f04f276ecb2
parent d60a7315d676b9d69dc37b0ebfa8a27afe7bbeed

pw_sys_io_stdio: Expand allowed uses beyond host

Select compatible targets via the constraint for the backend instead of
limiting to only hosts. There are embedded use cases where stdio output
makes sense (semi-hosting/simulators/etc).

Change-Id: I1d99dc054c808c8cfa1202422a596b210a745a18
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/208511
Reviewed-by: Ted Pudlik <tpudlik@google.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Commit-Queue: Austin Foxley <afoxley@google.com>

pw_sys_io/BUILD.bazel

diff --git a/pw_sys_io/BUILD.bazel b/pw_sys_io/BUILD.bazel
index 9bee6e0..ea6ce2d 100644
--- a/pw_sys_io/BUILD.bazel
+++ b/pw_sys_io/BUILD.bazel
@@ -24,6 +24,12 @@
 
 constraint_setting(
     name = "backend_constraint_setting",
+    default_constraint_value = "unspecified",
+)
+
+constraint_value(
+    name = "unspecified",
+    constraint_setting = ":backend_constraint_setting",
 )
 
 # TODO: pwbug.dev/328679085 - Remove this alias once no-one uses it.
@@ -69,6 +75,7 @@
         "//pw_sys_io_rp2040:backend": "@pigweed//pw_sys_io_rp2040",
         "//pw_sys_io_stm32cube:backend": "@pigweed//pw_sys_io_stm32cube",
         "//pw_sys_io_stdio:backend": "@pigweed//pw_sys_io_stdio",
+        ":unspecified": ":unspecified_backend",
         "//conditions:default": ":unspecified_backend",
     }),
     visibility = ["@pigweed//targets:__pkg__"],

pw_sys_io_stdio/BUILD.bazel

diff --git a/pw_sys_io_stdio/BUILD.bazel b/pw_sys_io_stdio/BUILD.bazel
index 1121003..8bf1e54 100644
--- a/pw_sys_io_stdio/BUILD.bazel
+++ b/pw_sys_io_stdio/BUILD.bazel
@@ -12,11 +12,6 @@
 # License for the specific language governing permissions and limitations under
 # the License.
 
-load(
-    "//pw_build:selects.bzl",
-    "TARGET_COMPATIBLE_WITH_HOST_SELECT",
-)
-
 package(default_visibility = ["//visibility:public"])
 
 licenses(["notice"])
@@ -29,7 +24,11 @@
 cc_library(
     name = "pw_sys_io_stdio",
     srcs = ["sys_io.cc"],
-    target_compatible_with = select(TARGET_COMPATIBLE_WITH_HOST_SELECT),
+    target_compatible_with = select({
+        ":backend": [],
+        "//pw_sys_io:unspecified": [],
+        "//conditions:default": ["@platforms//:incompatible"],
+    }),
     deps = [
         "//pw_sys_io:default_putget_bytes",
         "//pw_sys_io:pw_sys_io.facade",

pw_sys_io_stdio/docs.rst

diff --git a/pw_sys_io_stdio/docs.rst b/pw_sys_io_stdio/docs.rst
index eaa45af..b566b29 100644
--- a/pw_sys_io_stdio/docs.rst
+++ b/pw_sys_io_stdio/docs.rst
@@ -21,7 +21,12 @@
 This module requires relatively minimal setup:
 
 1. Write code against the ``pw_sys_io`` facade.
-2. Direct the ``pw_sys_io_BACKEND`` GN build arg to point to this backend.
+2. Setup build system to point to this backend.
+
+ - For GN, direct the ``pw_sys_io_BACKEND`` GN build arg to point here.
+ - For Bazel, the default backend multiplexer will automatically pick this stdio
+   backend for host builds. To use this backend on non-host platforms, add the
+   ``@pigweed//pw_sys_io_stdio:backend`` constraint_value to your platform.
 
 Module usage
 ============