Add extra_{exec,target}_compatible_with extensions (#240)

This adds `extra_exec_compatible_with` and
`extra_target_compatible_with` as extensions so that users can control
whether the toolchains generated by hermetic_cc_toolchain are selected.

This is intended to fix
#205

Author: ddunl

toolchain/defs.bzl

@@ -66,6 +66,8 @@ def toolchains(
         host_platform_sha256 = HOST_PLATFORM_SHA256,
         host_platform_ext = _HOST_PLATFORM_EXT,
         exec_platforms = {},
+        extra_exec_compatible_with = [],
+        extra_target_compatible_with = [],
         extra_target_settings = []):
     """
         Download zig toolchain and declare bazel toolchains.
@@ -86,6 +88,8 @@ def toolchains(
     zig_sdk_repository(
         name = "zig_sdk",
         exec_platforms = exec_platforms,
+        extra_exec_compatible_with = extra_exec_compatible_with,
+        extra_target_compatible_with = extra_target_compatible_with,
         extra_target_settings = extra_target_settings,
     )
 

toolchain/ext.bzl

@@ -22,11 +22,27 @@ _extra_target_settings = tag_class(
     doc = "Each setting is added to every toolchain to make them more restrictive",
 )
 
+_extra_target_compatible_with = tag_class(
+    attrs = {
+        "constraints": attr.label_list(),
+    },
+    doc = "Extra constraints added to every toolchain's `target_compatible_with`",
+)
+
+_extra_exec_compatible_with = tag_class(
+    attrs = {
+        "constraints": attr.label_list(),
+    },
+    doc = "Extra constraints added to every toolchain's `exec_compatible_with`",
+)
+
 def _toolchains_impl(mctx):
     exec_platforms = {}
     root_direct_deps = []
     root_direct_dev_deps = []
     is_non_dev_dependency = mctx.root_module_has_non_dev_dependency
+    extra_exec_compatible_with = []
+    extra_target_compatible_with = []
     extra_target_settings = []
 
     for mod in mctx.modules:
@@ -40,7 +56,18 @@ def _toolchains_impl(mctx):
             for tag in mod.tags.extra_target_settings:
                 extra_target_settings += tag.settings
 
-            repos = zig_toolchains(exec_platforms = exec_platforms, extra_target_settings = extra_target_settings)
+            for tag in mod.tags.extra_exec_compatible_with:
+                extra_exec_compatible_with += tag.constraints
+
+            for tag in mod.tags.extra_target_compatible_with:
+                extra_target_compatible_with += tag.constraints
+
+            repos = zig_toolchains(
+                exec_platforms = exec_platforms,
+                extra_exec_compatible_with = extra_exec_compatible_with,
+                extra_target_compatible_with = extra_target_compatible_with,
+                extra_target_settings = extra_target_settings,
+            )
 
             root_direct_deps = list(repos.public) if is_non_dev_dependency else []
             root_direct_dev_deps = list(repos.public) if not is_non_dev_dependency else []
@@ -59,6 +86,8 @@ toolchains = module_extension(
     implementation = _toolchains_impl,
     tag_classes = {
         "exec_platform": _exec_platform,
+        "extra_exec_compatible_with": _extra_exec_compatible_with,
+        "extra_target_compatible_with": _extra_target_compatible_with,
         "extra_target_settings": _extra_target_settings,
     },
 )

toolchain/libc_aware/toolchain/BUILD.bazel.tmpl

@@ -7,4 +7,9 @@ package(
     default_visibility = ["//visibility:public"],
 )
 
-declare_libc_aware_toolchains(configs = {configs}, extra_target_settings = {extra_target_settings})
+declare_libc_aware_toolchains(
+    configs = {configs},
+    extra_exec_compatible_with = {extra_exec_compatible_with},
+    extra_target_compatible_with = {extra_target_compatible_with},
+    extra_target_settings = {extra_target_settings},
+)

toolchain/private/repositories.bzl

@@ -2,6 +2,8 @@ load("@hermetic_cc_toolchain//toolchain:utils.bzl", "quote")
 load("@hermetic_cc_toolchain//toolchain/private:defs.bzl", "transform_arch_name", "transform_os_name")
 
 def _define_zig_toolchains(repository_ctx, configs, package = ""):
+    extra_exec_compatible_with = "[" + " ".join([quote(str(setting)) + "," for setting in repository_ctx.attr.extra_exec_compatible_with]) + "]"
+    extra_target_compatible_with = "[" + " ".join([quote(str(setting)) + "," for setting in repository_ctx.attr.extra_target_compatible_with]) + "]"
     extra_target_settings = "[" + " ".join([quote(str(setting)) + "," for setting in repository_ctx.attr.extra_target_settings]) + "]"
 
     repository_ctx.template(
@@ -10,6 +12,8 @@ def _define_zig_toolchains(repository_ctx, configs, package = ""):
         executable = False,
         substitutions = {
             "{configs}": repr(configs),
+            "{extra_exec_compatible_with}": extra_exec_compatible_with,
+            "{extra_target_compatible_with}": extra_target_compatible_with,
             "{extra_target_settings}": extra_target_settings,
         },
     )
@@ -20,6 +24,8 @@ def _define_zig_toolchains(repository_ctx, configs, package = ""):
         executable = False,
         substitutions = {
             "{configs}": repr(configs),
+            "{extra_exec_compatible_with}": extra_exec_compatible_with,
+            "{extra_target_compatible_with}": extra_target_compatible_with,
             "{extra_target_settings}": extra_target_settings,
         },
     )
@@ -96,6 +102,12 @@ zig_sdk_repository = repository_rule(
             doc = "Dictionary, where the keys are oses and the values are lists of supported architectures",
             mandatory = True,
         ),
+        "extra_exec_compatible_with": attr.label_list(
+            doc = "Additional constraints added to the `exec_compatible_with` attribute of each generated toolchain",
+        ),
+        "extra_target_compatible_with": attr.label_list(
+            doc = "Additional constraints added to the `target_compatible_with` attribute of each generated toolchain",
+        ),
         "extra_target_settings": attr.label_list(
             doc = "Additional settings to add to the generated toolchains, to make them more restrictive",
         ),

toolchain/toolchain/BUILD.bazel.tmpl

@@ -4,4 +4,9 @@ package(
     default_visibility = ["//visibility:public"],
 )
 
-declare_toolchains(configs = {configs}, extra_target_settings = {extra_target_settings})
+declare_toolchains(
+    configs = {configs},
+    extra_exec_compatible_with = {extra_exec_compatible_with},
+    extra_target_compatible_with = {extra_target_compatible_with},
+    extra_target_settings = {extra_target_settings},
+)

toolchain/toolchain/defs.bzl

@@ -1,6 +1,10 @@
 load("@hermetic_cc_toolchain//toolchain/private:defs.bzl", "target_structs")
 
-def declare_toolchains(configs = "", extra_target_settings = []):
+def declare_toolchains(
+        configs = "",
+        extra_exec_compatible_with = [],
+        extra_target_compatible_with = [],
+        extra_target_settings = []):
     for target_config in target_structs():
         gotarget = target_config.gotarget
         zigtarget = target_config.zigtarget
@@ -12,11 +16,15 @@ def declare_toolchains(configs = "", extra_target_settings = []):
         if hasattr(target_config, "libc_constraint"):
             extra_constraints = ["@zig_sdk//libc:unconstrained"]
 
-        _declare_toolchain(gotarget, zigtarget, target_config.constraint_values + extra_constraints, configs, extra_target_settings)
+        _declare_toolchain(gotarget, zigtarget, target_config.constraint_values + extra_constraints, configs, extra_exec_compatible_with, extra_target_compatible_with, extra_target_settings)
 
     _declare_zig_toolchain("zig", configs)
 
-def declare_libc_aware_toolchains(configs = "", extra_target_settings = []):
+def declare_libc_aware_toolchains(
+        configs = "",
+        extra_exec_compatible_with = [],
+        extra_target_compatible_with = [],
+        extra_target_settings = []):
     for target_config in target_structs():
         gotarget = target_config.gotarget
         zigtarget = target_config.zigtarget
@@ -25,15 +33,22 @@ def declare_libc_aware_toolchains(configs = "", extra_target_settings = []):
         # is only selected if libc is not expicitly set and another one that is
         # only selected if the specific libc variant is selected.
         if hasattr(target_config, "libc_constraint"):
-            _declare_toolchain(gotarget, zigtarget, target_config.constraint_values + [target_config.libc_constraint], configs, extra_target_settings)
+            _declare_toolchain(gotarget, zigtarget, target_config.constraint_values + [target_config.libc_constraint], configs, extra_exec_compatible_with, extra_target_compatible_with, extra_target_settings)
 
-def _declare_toolchain(gotarget, zigtarget, target_compatible_with, configs, extra_target_settings):
+def _declare_toolchain(
+        gotarget,
+        zigtarget,
+        target_compatible_with,
+        configs,
+        extra_exec_compatible_with,
+        extra_target_compatible_with,
+        extra_target_settings):
     # register two kinds of toolchain targets: Go and Zig conventions.
     # Go convention: amd64/arm64, linux/darwin
     native.toolchain(
         name = gotarget,
-        exec_compatible_with = ["{}//:exec_os".format(configs), "{}//:exec_cpu".format(configs)],
-        target_compatible_with = target_compatible_with,
+        exec_compatible_with = ["{}//:exec_os".format(configs), "{}//:exec_cpu".format(configs)] + extra_exec_compatible_with,
+        target_compatible_with = target_compatible_with + extra_target_compatible_with,
         target_settings = extra_target_settings,
         toolchain = "{}//:{}_cc".format(configs, zigtarget),
         toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
@@ -42,8 +57,8 @@ def _declare_toolchain(gotarget, zigtarget, target_compatible_with, configs, ext
     # Zig convention: x86_64/aarch64, linux/macos
     native.toolchain(
         name = zigtarget,
-        exec_compatible_with = ["{}//:exec_os".format(configs), "{}//:exec_cpu".format(configs)],
-        target_compatible_with = target_compatible_with,
+        exec_compatible_with = ["{}//:exec_os".format(configs), "{}//:exec_cpu".format(configs)] + extra_exec_compatible_with,
+        target_compatible_with = target_compatible_with + extra_target_compatible_with,
         target_settings = extra_target_settings,
         toolchain = "{}//:{}_cc".format(configs, zigtarget),
         toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",