Allows to provide Lipo tool location via custom toolchain.

rules/universal_binary.bzl

@@ -15,23 +15,48 @@
 """Implementation for macOS universal binary rule."""
 
 load("@bazel_skylib//lib:dicts.bzl", "dicts")
+load("@bazel_skylib//lib:shell.bzl", "shell")
 load("//lib:apple_support.bzl", "apple_support")
 load("//lib:lipo.bzl", "lipo")
 load("//lib:transitions.bzl", "macos_universal_transition")
 
 def _universal_binary_impl(ctx):
-    inputs = [
-        binary.files.to_list()[0]
-        for binary in ctx.split_attr.binary.values()
-    ]
+    inputs = []
+    for binary in ctx.split_attr.binary.values():
+        inputs += binary.files.to_list()
 
     if not inputs:
         fail("Target (%s) `binary` label ('%s') does not provide any " +
              "file for universal binary" % (ctx.attr.name, ctx.attr.binary))
 
     output = ctx.actions.declare_file(ctx.label.name)
 
-    if len(inputs) > 1:
+    lipo_toolchain = ctx.toolchains["//toolchain/lipo:toolchain_type"]
+
+    if len(inputs) > 1 and lipo_toolchain:
+        lipo_tool = lipo_toolchain.info.lipo
+
+        cmd = [
+            "mkdir -p {} &&".format(shell.quote(output.dirname)),
+            lipo_tool.path,
+            "-create",
+        ]
+        cmd.extend([
+            shell.quote(file.path)
+            for file in inputs
+        ])
+        cmd.extend([
+            "-output",
+            shell.quote(output.path),
+        ])
+
+        ctx.actions.run_shell(
+            command = " ".join(cmd),
+            mnemonic = "AppleLipo",
+            inputs = inputs + [lipo_tool],
+            outputs = [output],
+        )
+    elif len(inputs) > 1:
         lipo.create(
             actions = ctx.actions,
             apple_fragment = ctx.fragments.apple,
@@ -84,4 +109,7 @@ binary.
     executable = True,
     fragments = ["apple"],
     implementation = _universal_binary_impl,
+    toolchains = [
+        config_common.toolchain_type("//toolchain/lipo:toolchain_type", mandatory = False),
+    ],
 )

toolchain/lipo/BUILD

@@ -0,0 +1,4 @@
+toolchain_type(
+    name = "toolchain_type",
+    visibility = ["//visibility:public"],
+)

toolchain/lipo/lipo_toolchain.bzl

@@ -0,0 +1,48 @@
+"""Toolchain definition to provide Lipo tool location.
+
+Usage:
+
+    load("@build_bazel_apple_support//toolchain/lipo:lipo_toolchain.bzl", "lipo_toolchain")
+
+    lipo_toolchain(
+        name = "_lipo_toolchain",
+        lipo = ":lipo",
+    )
+
+    toolchain(
+        name = "lipo_toolchain",
+        toolchain = ":_lipo_toolchain",
+        toolchain_type = "@build_bazel_apple_support//toolchain/lipo:toolchain_type",
+        exec_compatible_with = [
+            "@platforms//os:macos",
+        ],
+        target_compatible_with = [
+            "@platforms//os:macos",
+        ],
+    )
+
+"""
+
+Info = provider(
+    fields = ["lipo"],
+    doc = "Tools info to locate xcode tools",
+)
+
+def _lipo_toolchain_impl(ctx):
+    toolchain_info = platform_common.ToolchainInfo(
+        info = Info(
+            lipo = ctx.file.lipo,
+        ),
+    )
+    return [toolchain_info]
+
+lipo_toolchain = rule(
+    doc = "Toolchain rule to provide Lipo tool location.",
+    implementation = _lipo_toolchain_impl,
+    attrs = {
+        "lipo": attr.label(
+            doc = "a label to lipo tool.",
+            allow_single_file = True,
+        ),
+    },
+)