Use the host_platform from @platforms in Bazel

* Upgrade to `platforms` 0.0.9
* `--host_platform` now defaults to `@bazel_tools//tools:host_platform`, which is an alias of `@platforms//host`
* `local_config_platform` (the repo rule) now just outputs a thin wrapper; `@local_config_platform//:host` is an alias of `@platforms//host`, and `@local_config_platform//:constraints.bzl` re-exports `@platforms//host:constraints.bzl`
* Removed all test mocks of `local_config_platform`. A follow-up will guard prod usage behind a flag.

Work towards #8766 and #18285.

PiperOrigin-RevId: 620316973
Change-Id: I6593f62569f31faee69e88a520a0f7f42009e05d

BUILD

@@ -271,7 +271,7 @@ platform(
     constraint_values = [
         ":highcpu_machine",
     ],
-    parents = ["@local_config_platform//:host"],
+    parents = ["@platforms//host"],
 )
 
 platform(

MODULE.bazel

@@ -16,7 +16,7 @@ bazel_dep(name = "rules_license", version = "0.0.7")
 bazel_dep(name = "bazel_skylib", version = "1.5.0")
 bazel_dep(name = "protobuf", version = "21.7", repo_name = "com_google_protobuf")
 bazel_dep(name = "grpc", version = "1.48.1.bcr.1", repo_name = "com_github_grpc_grpc")
-bazel_dep(name = "platforms", version = "0.0.8")
+bazel_dep(name = "platforms", version = "0.0.9")
 bazel_dep(name = "rules_pkg", version = "0.9.1")
 bazel_dep(name = "stardoc", version = "0.5.6", repo_name = "io_bazel_skydoc")
 bazel_dep(name = "zstd-jni", version = "1.5.2-3.bcr.1")

compile.sh

@@ -65,8 +65,8 @@ log "Building output/bazel"
 # host.
 bazel_build "src:bazel_nojdk${EXE_EXT}" \
   --action_env=PATH \
-  --host_platform=@local_config_platform//:host \
-  --platforms=@local_config_platform//:host \
+  --host_platform=@platforms//host \
+  --platforms=@platforms//host \
   || fail "Could not build Bazel"
 bazel_bin_path="$(get_bazel_bin_path)/src/bazel_nojdk${EXE_EXT}"
 [ -e "$bazel_bin_path" ] \

site/en/concepts/platforms.md

@@ -193,7 +193,8 @@ Project owners should define explicit
 they want to build for. These are then triggered with `--platforms`.
 
 When `--platforms` isn't set, Bazel defaults to a `platform` representing the
-local build machine. This is auto-generated at `@local_config_platform//:host`
+local build machine. This is auto-generated at `@platforms//host` (aliased as
+`@bazel_tools//tools:host_platform`)
 so there's no need to explicitly define it. It maps the local machine's `OS`
 and `CPU` with `constraint_value`s declared in
 [`@platforms`](https://github.com/bazelbuild/platforms){: .external}.

site/en/extending/platforms.md

@@ -106,23 +106,24 @@ systems. These are all located in
 [https://github.com/bazelbuild/platforms](https://github.com/bazelbuild/platforms){: .external}.
 
 Bazel ships with the following special platform definition:
-`@local_config_platform//:host`. This is the autodetected host platform value -
+`@platforms//host` (aliased as `@bazel_tools//tools:host_platform`). This is the
+autodetected host platform value -
 represents autodetected platform for the system Bazel is running on.
 
 ## Specifying a platform for a build {:#specifying-build-platform}
 
 You can specify the host and target platforms for a build using the following
 command-line flags:
 
-*  `--host_platform` - defaults to `@local_config_platform//:host`
-   *  `@local_config_platform` is a repo backed by a repo rule that detects the
-      host OS and CPU and writes the platform target.
-   *  It also creates `@local_config_platform//:constraints.bzl`, which exposes
+*  `--host_platform` - defaults to `@bazel_tools//tools:host_platform`
+   *  This target is aliased to `@platforms//host`, which is backed by a repo
+      rule that detects the host OS and CPU and writes the platform target.
+   *  There's also `@platforms//host:constraints.bzl`, which exposes
       an array called `HOST_CONSTRAINTS`, which can be used in other BUILD and
       Starlark files.
 *  `--platforms` - defaults to the host platform
    *  This means that when no other flags are set,
-      `@local_config_platform//:host` is the target platform.
+      `@platforms//host` is the target platform.
    *  If `--host_platform` is set and not `--platforms`, the value of
       `--host_platform` is both the host and target platform.
 

src/MODULE.tools

@@ -11,7 +11,7 @@ bazel_dep(name = "rules_proto", version = "4.0.0")
 bazel_dep(name = "rules_python", version = "0.22.1")
 
 bazel_dep(name = "buildozer", version = "6.4.0.2")
-bazel_dep(name = "platforms", version = "0.0.7")
+bazel_dep(name = "platforms", version = "0.0.9")
 bazel_dep(name = "protobuf", version = "3.19.6", repo_name = "com_google_protobuf")
 bazel_dep(name = "zlib", version = "1.3")
 

src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java

@@ -55,7 +55,7 @@ public static boolean platformIsDefault(Label platform) {
       name = "host_platform",
       oldName = "experimental_host_platform",
       converter = EmptyToNullLabelConverter.class,
-      defaultValue = "@local_config_platform//:host",
+      defaultValue = "@bazel_tools//tools:host_platform",
       documentationCategory = OptionDocumentationCategory.TOOLCHAIN,
       effectTags = {
         OptionEffectTag.AFFECTS_OUTPUTS,