Create hub repo for shell framework toolchains (#1066)

This simplifies the registration of the shell framework toolchains in
bzlmod.

MODULE.bazel

@@ -20,17 +20,11 @@ use_repo(
     "ninja_1.11.1_toolchains",
     "ninja_build_src",
     "pkgconfig_src",
-    "rules_foreign_cc_framework_toolchain_freebsd",
-    "rules_foreign_cc_framework_toolchain_linux",
-    "rules_foreign_cc_framework_toolchain_macos",
-    "rules_foreign_cc_framework_toolchain_windows",
+    "rules_foreign_cc_framework_toolchains",
 )
 
 register_toolchains(
-    "@rules_foreign_cc_framework_toolchain_freebsd//:toolchain",
-    "@rules_foreign_cc_framework_toolchain_linux//:toolchain",
-    "@rules_foreign_cc_framework_toolchain_macos//:toolchain",
-    "@rules_foreign_cc_framework_toolchain_windows//:toolchain",
+    "@rules_foreign_cc_framework_toolchains//:all",
     "@rules_foreign_cc//toolchains:built_make_toolchain",
     "@rules_foreign_cc//toolchains:built_meson_toolchain",
     "@rules_foreign_cc//toolchains:built_pkgconfig_toolchain",

foreign_cc/private/framework/toolchain.bzl

@@ -12,14 +12,6 @@ exports_files(["defs.bzl"])
 foreign_cc_framework_toolchain(
     name = "commands"
 )
-
-toolchain(
-    name = "toolchain",
-    toolchain_type = "@rules_foreign_cc//foreign_cc/private/framework:shell_toolchain",
-    toolchain = ":commands",
-    exec_compatible_with = {exec_compat},
-    target_compatible_with = {target_compat},
-)
 """
 
 _DEFS_BZL_CONTENT = """\
@@ -52,7 +44,6 @@ def _framework_toolchain_repository_impl(repository_ctx):
 
     repository_ctx.file("BUILD.bazel", _BUILD_FILE_CONTENT.format(
         exec_compat = repository_ctx.attr.exec_compatible_with,
-        target_compat = repository_ctx.attr.target_compatible_with,
     ))
 
 framework_toolchain_repository = repository_rule(
@@ -65,8 +56,38 @@ framework_toolchain_repository = repository_rule(
         "exec_compatible_with": attr.string_list(
             doc = "A list of constraint_values that must be present in the execution platform for this target.",
         ),
-        "target_compatible_with": attr.string_list(
-            doc = "A list of constraint_values that must be present in the target platform for this target to be considered compatible.",
+    },
+)
+
+_HUB_BUILD_FILE_CONTENT = """\
+toolchain(
+    name = "{item}",
+    toolchain_type = "@rules_foreign_cc//foreign_cc/private/framework:shell_toolchain",
+    toolchain = "@{item}//:commands",
+    exec_compatible_with = {exec_compat},
+)
+
+"""
+
+def _framework_toolchain_repository_hub_impl(repository_ctx):
+    """The implementation of `framework_toolchain_repository_hub`
+
+    Args:
+        repository_ctx (repository_ctx): The rule's context object
+    """
+
+    hub_build_content = ""
+    for item in TOOLCHAIN_MAPPINGS:
+        hub_build_content += _HUB_BUILD_FILE_CONTENT.format(item = item.repo_name, exec_compat = item.exec_compatible_with)
+
+    repository_ctx.file("BUILD.bazel", hub_build_content)
+
+framework_toolchain_repository_hub = repository_rule(
+    doc = "A repository rule which defines a `@rules_foreign_cc//foreign_cc/private/framework:shell_toolchain` hub which holds all the shell toolchains generated by `@rules_foreign_cc`.",
+    implementation = _framework_toolchain_repository_hub_impl,
+    attrs = {
+        "exec_compatible_with": attr.string_list(
+            doc = "A list of constraint_values that must be present in the execution platform for this target.",
         ),
     },
 )
@@ -78,17 +99,15 @@ def register_framework_toolchains(register_toolchains = True):
     Args:
         register_toolchains: Whether to call native.register_toolchains or not
     """
-    toolchains = []
 
     for item in TOOLCHAIN_MAPPINGS:
         framework_toolchain_repository(
             name = item.repo_name,
             commands_src = item.file,
             exec_compatible_with = item.exec_compatible_with,
-            target_compatible_with = item.target_compatible_with,
         )
 
-        toolchains.append("@{}//:toolchain".format(item.repo_name))
+    framework_toolchain_repository_hub(name = "rules_foreign_cc_framework_toolchains")
 
     if register_toolchains:
-        native.register_toolchains(*toolchains)
+        native.register_toolchains("@rules_foreign_cc_framework_toolchains//:all")

foreign_cc/private/framework/toolchains/mappings.bzl

@@ -1,13 +1,12 @@
 """A module defining default toolchain info for the foreign_cc framework"""
 
-def _toolchain_mapping(file, repo_name, exec_compatible_with = [], target_compatible_with = []):
+def _toolchain_mapping(file, repo_name, exec_compatible_with = []):
     """Mapping of toolchain definition files to platform constraints
 
     Args:
         file (str): Toolchain definition file
         repo_name (str): name of repository to create for this toolchain
         exec_compatible_with (list): A list of compatible execution platform constraints.
-        target_compatible_with (list): Compatible target platform constraints
 
     Returns:
         struct: A collection of toolchain data
@@ -16,7 +15,6 @@ def _toolchain_mapping(file, repo_name, exec_compatible_with = [], target_compat
         file = file,
         repo_name = repo_name,
         exec_compatible_with = exec_compatible_with,
-        target_compatible_with = target_compatible_with,
     )
 
 # This list is the single entrypoint for all foreign_cc framework toolchains.