feat: support target platform transitions in the zig_configure* rule family

.bazelrc

@@ -7,8 +7,8 @@ import %workspace%/.bazelrc.flags
 # Deleted packages for integration tests.
 # To update these lines, execute
 # `bazel run @contrib_rules_bazel_integration_test//tools:update_deleted_packages`
-build --deleted_packages=e2e/workspace,e2e/workspace/configure-mode,e2e/workspace/configure-threaded,e2e/workspace/linker-script,e2e/workspace/multiple-sources-and-packages-test,e2e/workspace/multiple-sources-binary,e2e/workspace/simple-binary,e2e/workspace/simple-library,e2e/workspace/simple-test,e2e/workspace/transitive-zig-packages-binary,e2e/workspace/transitive-zig-packages-binary/hello-world,e2e/workspace/transitive-zig-packages-binary/hello-world/data,e2e/workspace/transitive-zig-packages-binary/hello-world/data/hello,e2e/workspace/transitive-zig-packages-binary/hello-world/data/world,e2e/workspace/transitive-zig-packages-binary/hello-world/io,e2e/workspace/zig-package-binary,e2e/workspace/zig-package-binary/data,e2e/workspace/zig-package-binary/io,zig/tests/integration_tests/workspace
-query --deleted_packages=e2e/workspace,e2e/workspace/configure-mode,e2e/workspace/configure-threaded,e2e/workspace/linker-script,e2e/workspace/multiple-sources-and-packages-test,e2e/workspace/multiple-sources-binary,e2e/workspace/simple-binary,e2e/workspace/simple-library,e2e/workspace/simple-test,e2e/workspace/transitive-zig-packages-binary,e2e/workspace/transitive-zig-packages-binary/hello-world,e2e/workspace/transitive-zig-packages-binary/hello-world/data,e2e/workspace/transitive-zig-packages-binary/hello-world/data/hello,e2e/workspace/transitive-zig-packages-binary/hello-world/data/world,e2e/workspace/transitive-zig-packages-binary/hello-world/io,e2e/workspace/zig-package-binary,e2e/workspace/zig-package-binary/data,e2e/workspace/zig-package-binary/io,zig/tests/integration_tests/workspace
+build --deleted_packages=e2e/workspace,e2e/workspace/configure-mode,e2e/workspace/configure-target,e2e/workspace/configure-threaded,e2e/workspace/linker-script,e2e/workspace/multiple-sources-and-packages-test,e2e/workspace/multiple-sources-binary,e2e/workspace/simple-binary,e2e/workspace/simple-library,e2e/workspace/simple-test,e2e/workspace/transitive-zig-packages-binary,e2e/workspace/transitive-zig-packages-binary/hello-world,e2e/workspace/transitive-zig-packages-binary/hello-world/data,e2e/workspace/transitive-zig-packages-binary/hello-world/data/hello,e2e/workspace/transitive-zig-packages-binary/hello-world/data/world,e2e/workspace/transitive-zig-packages-binary/hello-world/io,e2e/workspace/zig-package-binary,e2e/workspace/zig-package-binary/data,e2e/workspace/zig-package-binary/io,zig/tests/integration_tests/workspace
+query --deleted_packages=e2e/workspace,e2e/workspace/configure-mode,e2e/workspace/configure-target,e2e/workspace/configure-threaded,e2e/workspace/linker-script,e2e/workspace/multiple-sources-and-packages-test,e2e/workspace/multiple-sources-binary,e2e/workspace/simple-binary,e2e/workspace/simple-library,e2e/workspace/simple-test,e2e/workspace/transitive-zig-packages-binary,e2e/workspace/transitive-zig-packages-binary/hello-world,e2e/workspace/transitive-zig-packages-binary/hello-world/data,e2e/workspace/transitive-zig-packages-binary/hello-world/data/hello,e2e/workspace/transitive-zig-packages-binary/hello-world/data/world,e2e/workspace/transitive-zig-packages-binary/hello-world/io,e2e/workspace/zig-package-binary,e2e/workspace/zig-package-binary/data,e2e/workspace/zig-package-binary/io,zig/tests/integration_tests/workspace
 
 # Load any settings specific to the current user.
 # .bazelrc.user should appear in .gitignore so that settings are not shared with team members

e2e/workspace/configure-target/BUILD.bazel

@@ -0,0 +1,104 @@
+load("@bazel_skylib//rules:build_test.bzl", "build_test")
+load("@bazel_skylib//rules:diff_test.bzl", "diff_test")
+load(
+    "@rules_zig//zig:defs.bzl",
+    "zig_binary",
+    "zig_configure_binary",
+    "zig_configure_test",
+    "zig_test",
+)
+
+platform(
+    name = "aarch64-linux",
+    constraint_values = [
+        "@platforms//os:linux",
+        "@platforms//cpu:aarch64",
+    ],
+)
+
+zig_binary(
+    name = "read_elf_arch",
+    main = "read_elf_arch.zig",
+)
+
+# TODO[AH] Test target transition on zig_library.
+#   Open question: how to extract the target platform from .a file?
+
+# ----------------------------------------------------------
+# zig_configure_binary
+
+zig_binary(
+    name = "binary",
+    main = "main.zig",
+    tags = ["manual"],
+)
+
+zig_configure_binary(
+    name = "binary_aarch64-linux",
+    actual = ":binary",
+    tags = ["manual"],
+    target = ":aarch64-linux",
+)
+
+build_test(
+    name = "binary_aarch64-linux_build_test",
+    targets = [
+        ":binary_aarch64-linux",
+    ],
+)
+
+genrule(
+    name = "binary_aarch64-linux_arch",
+    srcs = [":binary_aarch64-linux"],
+    outs = ["binary_aarch64-linux_arch.actual"],
+    cmd = "$(execpath :read_elf_arch) $(SRCS) > $(OUTS)",
+    tools = [":read_elf_arch"],
+)
+
+diff_test(
+    name = "binary_aarch64-linux_arch_test",
+    file1 = ":binary_aarch64-linux_arch.expected",
+    file2 = ":binary_aarch64-linux_arch.actual",
+)
+
+# TODO[AH] Test another operating system
+
+# ----------------------------------------------------------
+# zig_configure_test
+
+zig_test(
+    name = "test",
+    main = "main.zig",
+    tags = ["manual"],
+)
+
+zig_configure_test(
+    name = "test_aarch64-linux",
+    actual = ":test",
+    tags = ["manual"],
+    target = ":aarch64-linux",
+)
+
+build_test(
+    name = "test_aarch64-linux_build_test",
+    targets = [
+        ":test_aarch64-linux",
+    ],
+)
+
+genrule(
+    name = "test_aarch64-linux_arch",
+    testonly = True,
+    srcs = [":test_aarch64-linux"],
+    outs = ["test_aarch64-linux_arch.actual"],
+    cmd = "$(execpath :read_elf_arch) $(SRCS) > $(OUTS)",
+    tools = [":read_elf_arch"],
+)
+
+diff_test(
+    name = "test_aarch64-linux_arch_test",
+    file1 = ":test_aarch64-linux_arch.expected",
+    file2 = ":test_aarch64-linux_arch.actual",
+)
+
+# TODO[AH] Test another operating system

e2e/workspace/configure-target/binary_aarch64-linux_arch.expected

@@ -0,0 +1 @@
+AARCH64

e2e/workspace/configure-target/main.zig

@@ -0,0 +1,5 @@
+const std = @import("std");
+
+pub fn main() !void {
+    try std.io.getStdOut().writer().print("Hello world!\n", .{});
+}

e2e/workspace/configure-target/read_elf_arch.zig

@@ -0,0 +1,23 @@
+const std = @import("std");
+const elf = std.elf;
+
+pub fn main() !void {
+    var args = try std.process.argsAlloc(std.heap.page_allocator);
+    defer std.process.argsFree(std.heap.page_allocator, args);
+
+    if (args.len < 2) {
+        try std.io.getStdErr().writer().print("Usage: {s} <binary_path>\n", .{args[0]});
+        return;
+    }
+
+    try printMachineType(args[1]);
+}
+
+fn printMachineType(binary_path: []const u8) !void {
+    const file = try std.fs.cwd().openFile(binary_path, .{});
+    defer file.close();
+
+    const elf_header = try elf.Header.read(file);
+
+    try std.io.getStdOut().writer().print("{s}\n", .{@tagName(elf_header.machine)});
+}

e2e/workspace/configure-target/test_aarch64-linux_arch.expected

@@ -0,0 +1 @@
+AARCH64

zig/private/zig_configure.bzl

@@ -8,6 +8,8 @@ DOC = """\
 
 def _zig_transition_impl(settings, attr):
     result = dict(settings)
+    if attr.target:
+        result["//command_line_option:platforms"] = str(attr.target)
     if attr.mode:
         result["//zig/settings:mode"] = attr.mode
     if attr.threaded:
@@ -17,10 +19,12 @@ def _zig_transition_impl(settings, attr):
 _zig_transition = transition(
     implementation = _zig_transition_impl,
     inputs = [
+        "//command_line_option:platforms",
         "//zig/settings:mode",
         "//zig/settings:threaded",
     ],
     outputs = [
+        "//command_line_option:platforms",
         "//zig/settings:mode",
         "//zig/settings:threaded",
     ],
@@ -34,6 +38,10 @@ def _make_attrs(*, executable, test):
             executable = executable,
             mandatory = True,
         ),
+        "target": attr.label(
+            doc = "The target platform",
+            mandatory = False,
+        ),
         "mode": attr.string(
             doc = "The build mode setting",
             mandatory = False,