Update toolchains support for latest rules_apple and transitions (#848)

Prepares our mac and xplat toolchains for Bazel 7

Changes:

- Replace usage of `"@bazel_tools//tools/cpp:current_cc_toolchain"` with
`"@build_bazel_rules_apple//apple:default_cc_toolchain_forwarder"`
- Rename `_toolchain` to `_mac_toolchain`, this matches rules_apple and
better represents that the toolchain is for the host platform
- Add `cfg = "exec"` to the mac and xplat toolchains
- This is required to fix toolchain resolution errors on Bazel 7. These
toolchains are for the host and so `exec` is correct here. This is the
same cfg they use in rules_apple

rules/framework.bzl

@@ -23,7 +23,7 @@ load("@build_bazel_rules_apple//apple/internal:rule_support.bzl", "rule_support"
 load("@build_bazel_rules_apple//apple/internal:apple_toolchains.bzl", "AppleMacToolsToolchainInfo", "AppleXPlatToolsToolchainInfo")
 load("@build_bazel_rules_apple//apple/internal:swift_support.bzl", "swift_support")
 load("@build_bazel_rules_apple//apple/internal/utils:clang_rt_dylibs.bzl", "clang_rt_dylibs")
-load("@build_bazel_rules_apple//apple/internal:providers.bzl", "AppleBundleInfo", "IosFrameworkBundleInfo", "new_applebundleinfo", "new_iosframeworkbundleinfo")
+load("@build_bazel_rules_apple//apple/internal:providers.bzl", "AppleBundleInfo", "ApplePlatformInfo", "IosFrameworkBundleInfo", "new_applebundleinfo", "new_iosframeworkbundleinfo")
 load("@build_bazel_rules_swift//swift:swift.bzl", "SwiftInfo", "swift_clang_module_aspect", "swift_common")
 load(
     "@build_bazel_rules_apple//apple/internal/aspects:resource_aspect.bzl",
@@ -588,7 +588,7 @@ def _merge_root_infoplists(ctx):
     bundle_name = ctx.attr.framework_name
     current_apple_platform = transition_support.current_apple_platform(apple_fragment = ctx.fragments.apple, xcode_config = ctx.attr._xcode_config)
     platform_type = str(current_apple_platform.platform.platform_type)
-    apple_mac_toolchain_info = ctx.attr._toolchain[AppleMacToolsToolchainInfo]
+    apple_mac_toolchain_info = ctx.attr._mac_toolchain[AppleMacToolsToolchainInfo]
     if hasattr(rule_support, "rule_descriptor_no_ctx"):
         descriptor_fn = rule_support.rule_descriptor_no_ctx
     else:
@@ -662,7 +662,7 @@ def _bundle_dynamic_framework(ctx, is_extension_safe, avoid_deps):
     Currently, this doesn't include headers or other interface files.
     """
     actions = ctx.actions
-    apple_mac_toolchain_info = ctx.attr._toolchain[AppleMacToolsToolchainInfo]
+    apple_mac_toolchain_info = ctx.attr._mac_toolchain[AppleMacToolsToolchainInfo]
     apple_xplat_toolchain_info = ctx.attr._xplat_toolchain[AppleXPlatToolsToolchainInfo]
     bin_root_path = ctx.bin_dir.path
     bundle_id = ctx.attr.bundle_id
@@ -1205,7 +1205,8 @@ that this target depends on.
         ),
         "_child_configuration_dummy": attr.label(
             cfg = transition_support.split_transition,
-            default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
+            providers = [cc_common.CcToolchainInfo, ApplePlatformInfo],
+            default = Label("@build_bazel_rules_apple//apple:default_cc_toolchain_forwarder"),
         ),
         "bundle_id": attr.string(
             mandatory = False,
@@ -1234,13 +1235,15 @@ the framework as a dependency.""",
             default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
             doc = "Needed to allow this rule to have an incoming edge configuration transition.",
         ),
-        "_toolchain": attr.label(
+        "_mac_toolchain": attr.label(
             default = Label("@build_bazel_rules_apple//apple/internal:mac_tools_toolchain"),
             providers = [[AppleMacToolsToolchainInfo]],
+            cfg = "exec",
         ),
         "_xplat_toolchain": attr.label(
             default = Label("@build_bazel_rules_apple//apple/internal:xplat_tools_toolchain"),
             providers = [[AppleXPlatToolsToolchainInfo]],
+            cfg = "exec",
         ),
         "platform_type": attr.string(
             mandatory = False,
@@ -1265,6 +1268,7 @@ the framework as a dependency.""",
             executable = True,
         ),
         "_cc_toolchain": attr.label(
+            providers = [cc_common.CcToolchainInfo],
             default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
             doc = """\
 The C++ toolchain from which linking flags and other tools needed by the Swift

rules/framework/BUILD.bazel

@@ -15,6 +15,7 @@ bzl_library(
         "//rules:features",
         "//rules:providers",
         "@bazel_tools//tools/cpp:toolchain_utils.bzl",
+        "@build_bazel_rules_apple//apple",
         "@build_bazel_rules_swift//swift",
     ],
 )

rules/framework/vfs_overlay.bzl

@@ -435,6 +435,7 @@ framework_vfs_overlay = rule(
         "private_hdrs": attr.label_list(allow_files = True, default = []),
         "deps": attr.label_list(allow_files = True, default = []),
         "_cc_toolchain": attr.label(
+            providers = [cc_common.CcToolchainInfo],
             default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
             doc = """\
 The C++ toolchain from which linking flags and other tools needed by the Swift

rules/precompiled_apple_resource_bundle.bzl

@@ -83,7 +83,7 @@ def _precompiled_apple_resource_bundle_impl(ctx):
         include_executable_name = False,
     )
 
-    apple_mac_toolchain_info = ctx.attr._toolchain[AppleMacToolsToolchainInfo]
+    apple_mac_toolchain_info = ctx.attr._mac_toolchain[AppleMacToolsToolchainInfo]
     partial_output = partial.call(
         partials.resources_partial(
             apple_mac_toolchain_info = apple_mac_toolchain_info,
@@ -283,9 +283,10 @@ the bundle as a dependency.""",
             default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
             doc = "Needed to allow this rule to have an incoming edge configuration transition.",
         ),
-        _toolchain = attr.label(
+        _mac_toolchain = attr.label(
             default = Label("@build_bazel_rules_apple//apple/internal:mac_tools_toolchain"),
             providers = [[AppleMacToolsToolchainInfo]],
+            cfg = "exec",
         ),
     )),
 )