Implement local_config_platform in @platforms (#86)

* POC: implement local_config_platform in @platforms

* missing colons

* move stuff around

* the repo rule need not be public

* attempt at a test setup...

* whoops

* newlines

* comments

* more comments

.bazelci/presubmit.yml

@@ -1,46 +1,35 @@
----
-#
-# Bazel releases
-#
-lts: &lts
-  bazel: latest
-
-rolling: &rolling
-  bazel: rolling
-
-
-targets: &targets
+tasks:
+  ubuntu:
+    platform: ubuntu2004
     build_targets:
     - "//..."
-
-
-tasks:
-  ubuntu_lts:
-    name: ubuntu_lts
-    platform: ubuntu2004
-    <<: *lts
-    <<: *targets
-  ubuntu_rolling:
-    name: ubuntu_rolling
-    platform: ubuntu2004
-    <<: *rolling
-    <<: *targets
-  macos_lts:
-    name: macos_lts
+    test_targets:
+    - "//..."
+    environment:
+      EXPECTED_HOST_CONSTRAINTS: '["@platforms//cpu:x86_64", "@platforms//os:linux"]'
+  macos:
     platform: macos
-    <<: *lts
-    <<: *targets
-  windows_lts:
-    name: windows_lts
+    build_targets:
+    - "//..."
+    test_targets:
+    - "//..."
+    environment:
+      EXPECTED_HOST_CONSTRAINTS: '["@platforms//cpu:x86_64", "@platforms//os:osx"]'
+  macos_arm64:
+    platform: macos_arm64
+    build_targets:
+    - "//..."
+    test_targets:
+    - "//..."
+    environment:
+      EXPECTED_HOST_CONSTRAINTS: '["@platforms//cpu:aarch64", "@platforms//os:osx"]'
+  windows:
     platform: windows
-    <<: *lts
-    <<: *targets
-  check_bzlmod:
-    name: check_bzlmod
-    # No need to check bzlmod on every platform. This repository only holds
-    # constants and has no per-platform behavior.
-    platform: ubuntu2004
-    <<: *rolling
-    <<: *targets
-    build_flags:
-    - "--enable_bzlmod"
+    build_targets:
+    - "//..."
+    # We don't run this test on Windows, because amazingly, sh_test doesn't work on Windows for exactly
+    # the @platforms repo (see https://github.com/bazelbuild/platforms/pull/86#issuecomment-2011954684)
+    #test_targets:
+    #- "//..."
+    #environment:
+    #  EXPECTED_HOST_CONSTRAINTS: '["@platforms//cpu:x86_64", "@platforms//os:windows"]'

BUILD

@@ -25,6 +25,7 @@ filegroup(
         "WORKSPACE",
         "//cpu:srcs",
         "//os:srcs",
+        "//host:srcs",
     ],
 )
 

MODULE.bazel

@@ -1,7 +1,11 @@
 module(
     name = "platforms",
-    version = "0.0.8",  # keep in sync with version.bzl
+    version = "0.0.9",  # keep in sync with version.bzl
     compatibility_level = 1,
 )
 
 bazel_dep(name = "rules_license", version = "0.0.7")
+
+host_platform = use_extension("//host:extension.bzl", "host_platform")
+use_repo(host_platform, "host_platform")
+

distro/makerel.sh

@@ -19,7 +19,7 @@ fi
 
 
 dist_file="/tmp/platforms-${version}.tar.gz"
-tar czf "$dist_file" BUILD LICENSE MODULE.bazel WORKSPACE WORKSPACE.bzlmod version.bzl cpu os
+tar czf "$dist_file" BUILD LICENSE MODULE.bazel WORKSPACE WORKSPACE.bzlmod version.bzl cpu os host
 sha256=$(shasum -a256 "$dist_file" | cut -d' ' -f1)
 
 path="github.com/bazelbuild/platforms/releases/download/$version/platforms-$version.tar.gz"

host/BUILD.bazel

@@ -0,0 +1,18 @@
+# Host platform detection
+
+load("@host_platform//:constraints.bzl", "HOST_CONSTRAINTS")
+
+package(default_visibility = ["//visibility:public"])
+
+exports_files(["constraints.bzl", "extension.bzl"])
+
+filegroup(
+    name = "srcs",
+    srcs = glob(["**"]),
+)
+
+platform(
+    name = "host",
+    constraint_values = HOST_CONSTRAINTS,
+)
+

host/constraints.bzl

@@ -0,0 +1,4 @@
+load("@host_platform//:constraints.bzl", _host_constraints = "HOST_CONSTRAINTS")
+
+HOST_CONSTRAINTS = _host_constraints
+

host/extension.bzl

@@ -0,0 +1,67 @@
+def _translate_cpu(arch):
+    if arch in ["i386", "i486", "i586", "i686", "i786", "x86"]:
+        return "x86_32"
+    if arch in ["amd64", "x86_64", "x64"]:
+        return "x86_64"
+    if arch in ["ppc", "ppc64", "ppc64le"]:
+        return "ppc"
+    if arch in ["arm", "armv7l"]:
+        return "arm"
+    if arch in ["aarch64"]:
+        return "aarch64"
+    if arch in ["s390x", "s390"]:
+        return "s390x"
+    if arch in ["mips64el", "mips64"]:
+        return "mips64"
+    if arch in ["riscv64"]:
+        return "riscv64"
+    return None
+
+def _translate_os(os):
+    if os.startswith("mac os"):
+        return "osx"
+    if os.startswith("freebsd"):
+        return "freebsd"
+    if os.startswith("openbsd"):
+        return "openbsd"
+    if os.startswith("linux"):
+        return "linux"
+    if os.startswith("windows"):
+        return "windows"
+    return None
+
+def _host_platform_repo_impl(rctx):
+    cpu = _translate_cpu(rctx.os.arch)
+    os = _translate_os(rctx.os.name)
+
+    cpu = "" if cpu == None else "  '@platforms//cpu:%s',\n" % cpu
+    os = "" if os == None else "  '@platforms//os:%s',\n" % os
+
+    rctx.file("BUILD.bazel", """
+# DO NOT EDIT: automatically generated BUILD file
+exports_files(["constraints.bzl"])
+""")
+
+    rctx.file("constraints.bzl", """
+# DO NOT EDIT: automatically generated constraints list
+HOST_CONSTRAINTS = [
+%s%s]
+""" % (cpu, os))
+
+host_platform_repo = repository_rule(
+    implementation = _host_platform_repo_impl,
+    doc = """Generates constraints for the host platform. The constraints.bzl
+file contains a single <code>HOST_CONSTRAINTS</code> variable, which is a
+list of strings, each of which is a label to a <code>constraint_value</code>
+for the host platform.""",
+)
+
+def _host_platform_impl(_mctx):
+    host_platform_repo(name = "host_platform")
+
+host_platform = module_extension(
+    implementation = _host_platform_impl,
+    doc = """Generates a <code>host_platform_repo</code> repo named
+<code>host_platform</code>, containing constraints for the host platform.""",
+)
+

tests/BUILD

@@ -1,4 +1,5 @@
 load("//:version.bzl", "version")
+load("//host:constraints.bzl", "HOST_CONSTRAINTS")
 
 package(default_visibility = ["//visibility:private"])
 
@@ -19,3 +20,10 @@ genrule(
         "//:MODULE.bazel",
     ],
 )
+
+sh_test(
+    name = "host_constraints_test",
+    srcs = ["host_constraints_test.sh"],
+    env = {"ACTUAL_HOST_CONSTRAINTS": repr(HOST_CONSTRAINTS)},
+    env_inherit = ["EXPECTED_HOST_CONSTRAINTS"],
+)

tests/host_constraints_test.sh

@@ -0,0 +1,3 @@
+echo actual host constraints: ${ACTUAL_HOST_CONSTRAINTS}
+echo expected host constraints: ${EXPECTED_HOST_CONSTRAINTS}
+test "${ACTUAL_HOST_CONSTRAINTS}" == "${EXPECTED_HOST_CONSTRAINTS}"

version.bzl

@@ -13,4 +13,4 @@
 # limitations under the License.
 """The version of bazelbuild/platforms."""
 
-version = "0.0.8"
+version = "0.0.9"