feat: Adds build variable expansion

MODULE.bazel

@@ -4,4 +4,5 @@ module(
 )
 
 bazel_dep(name = "rules_cc", version = "0.0.4")
+bazel_dep(name = "bazel_skylib", version = "1.4.1")
 bazel_dep(name = "stardoc", version = "0.5.3")

WORKSPACE

@@ -4,6 +4,19 @@ load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
 load("//third_party:test_repos.bzl", "test_repos")
 
+http_archive(
+    name = "bazel_skylib",
+    sha256 = "b8a1527901774180afc798aeb28c4634bdccf19c4d98e7bdd1ce79d1fe9aaad7",
+    urls = [
+        "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/1.4.1/bazel-skylib-1.4.1.tar.gz",
+        "https://github.com/bazelbuild/bazel-skylib/releases/download/1.4.1/bazel-skylib-1.4.1.tar.gz",
+    ],
+)
+
+load("@bazel_skylib//:workspace.bzl", "bazel_skylib_workspace")
+
+bazel_skylib_workspace()
+
 http_archive(
     name = "io_bazel_stardoc",
     sha256 = "3fd8fec4ddec3c670bd810904e2e33170bedfe12f90adf943508184be458c8bb",

cc/BUILD.bazel

@@ -2,6 +2,7 @@ load("@modular_cc_toolchain//cc:features.bzl", "cc_feature", "action_mux")
 load("//cc:action_names.bzl", "ACTION_NAME_GROUPS")
 load("//cc:actions.bzl", "cc_action_config")
 load("@rules_cc//cc:action_names.bzl", "ACTION_NAMES")
+load("//cc:toolchain.bzl", "cc_toolchain_config")
 
 cc_feature(
     name = "garbage_collect_sections",
@@ -18,14 +19,24 @@ cc_feature(
 cc_action_config(
     name = "default_clang",
     action_tools = {
-        ACTION_NAMES.c_compile: "@clang_llvm_x86_64_linux_gnu_ubuntu//:bin/clang",
+        ACTION_NAMES.c_compile: "@clang_llvm_x86_64_linux_gnu_ubuntu//:cc",
     }
 )
 
+cc_toolchain_config(
+    name = "test_toolchain_config",
+    cc_features = [
+        ":garbage_collect_sections",
+    ],
+    action_configs = [
+        ":default_clang",
+    ]
+)
+
 filegroup(
     name = "bzl_srcs",
     srcs = glob(["*.bzl"]),
     visibility = ["//visibility:public"],
 )
 
-exports_files(glob(["*.bzl"])) 
+exports_files(glob(["*.bzl"])) 

cc/common_features/BUILD.bazel

@@ -0,0 +1,36 @@
+load("@modular_cc_toolchain//cc:features.bzl", "cc_feature", "action_mux")
+load("//cc:action_names.bzl", "ACTION_NAME_GROUPS")
+load("@rules_cc//cc:action_names.bzl", "ACTION_NAMES")
+
+cc_feature(
+    name = "garbage_collect_sections",
+    action_flags = action_mux({
+        # Put each function and global var in their own linker section.
+        ACTION_NAME_GROUPS.all_cc_compile_actions: ["-ffunction-sections", "-fdata-sections"],
+        # Remove unused functions/symbols from linked binary.
+        ACTION_NAME_GROUPS.all_cc_link_actions: ["-Wl,--gc-sections"],
+    }),
+    doc = "Place each function in it's own section so that the linker can discard unused functions",
+)
+
+cc_feature(
+    name = "dependency_file",
+    enabled = True,
+    action_flags = action_mux({
+        (ACTION_NAMES.assemble,
+        ACTION_NAMES.preprocess_assemble,
+        ACTION_NAMES.c_compile,
+        ACTION_NAMES.cpp_compile,
+        ACTION_NAMES.cpp_module_compile,
+        ACTION_NAMES.objc_compile,
+        ACTION_NAMES.objcpp_compile,
+        ACTION_NAMES.cpp_header_parsing,
+        ACTION_NAMES.clif_match): [
+            "-MD",
+            "-MF",
+            "%{dependency_file}",
+        ]
+    })
+)
+
+

cc/features.bzl

@@ -2,11 +2,79 @@
 
 load(
     "@rules_cc//cc:cc_toolchain_config_lib.bzl",
-    "FeatureInfo",
+    "FeatureSetInfo",
     "feature",
+    "feature_set",
     "flag_group",
     "flag_set",
 )
+load(
+    "@rules_cc//cc:action_names.bzl",
+    "ACTION_NAMES",
+    "ACTION_NAME_GROUPS",
+)
+
+ALL_COMPILE_ACTIONS = ACTION_NAME_GROUPS.all_cc_compile_actions + \
+                      ACTION_NAME_GROUPS.all_cpp_compile_actions
+
+ALL_SYSROOT_ACTIONS = ACTION_NAME_GROUPS.all_cc_compile_actions + \
+                      ACTION_NAME_GROUPS.all_cc_link_actions + \
+                      ACTION_NAME_GROUPS.all_cpp_compile_actions + \
+                      ACTION_NAME_GROUPS.cc_link_executable_actions + \
+                      ACTION_NAME_GROUPS.dynamic_library_link_actions + \
+                      ACTION_NAME_GROUPS.nodeps_dynamic_library_link_actions + \
+                      ACTION_NAME_GROUPS.transitive_link_actions
+
+ALL_LINK_ACTIONS = ACTION_NAME_GROUPS.all_cc_link_actions + \
+                   ACTION_NAME_GROUPS.cc_link_executable_actions + \
+                   ACTION_NAME_GROUPS.dynamic_library_link_actions
+
+# Extracted from: https://bazel.build/docs/cc-toolchain-config-reference#cctoolchainconfiginfo-build-variables
+FLAG_VARS = {
+    "%{source_file}": ALL_COMPILE_ACTIONS,
+    "%{input_file}": ACTION_NAMES.strip,
+    "%{output_file}": ALL_COMPILE_ACTIONS,
+    "%{output_assembly_file}": ALL_COMPILE_ACTIONS,
+    "%{output_preprocess_file}": ALL_COMPILE_ACTIONS,
+    "%{dependency_file}": ALL_COMPILE_ACTIONS,
+    "%{pic}": ALL_COMPILE_ACTIONS,
+    "%{gcov_gcno_file}": ALL_COMPILE_ACTIONS,
+    "%{per_object_debug_info_file}": ALL_COMPILE_ACTIONS,
+    "%{sysroot}": ALL_SYSROOT_ACTIONS,
+    "%{def_file_path}": ALL_LINK_ACTIONS,
+    "%{linker_param_file}": ALL_LINK_ACTIONS,
+    "%{output_execpath}": ALL_LINK_ACTIONS,
+    "%{generate_interface_library}": ALL_LINK_ACTIONS,
+    "%{interface_library_builder_path}": ALL_LINK_ACTIONS,
+    "%{interface_library_input_path}": ALL_LINK_ACTIONS,
+    "%{interface_library_output_path}": ALL_LINK_ACTIONS,
+    "%{force_pic}": ALL_LINK_ACTIONS,
+    "%{strip_debug_symbols}": ALL_LINK_ACTIONS,
+    "%{is_cc_test}": ALL_LINK_ACTIONS,
+    "%{is_using_fission}": ALL_LINK_ACTIONS + ALL_LINK_ACTIONS,
+    "%{fdo_instrument_path}": ALL_COMPILE_ACTIONS + ALL_LINK_ACTIONS,
+    "%{fdo_prefetch_hints_path}": ALL_COMPILE_ACTIONS,
+    "%{csfdo_instrument_path}": ALL_COMPILE_ACTIONS + ALL_LINK_ACTIONS,
+}
+
+# Extracted from: https://bazel.build/docs/cc-toolchain-config-reference#cctoolchainconfiginfo-build-variables
+FLAG_SEQUENCE_VARS = {
+    "%{includes}": ALL_COMPILE_ACTIONS,
+    "%{include_paths}": ALL_COMPILE_ACTIONS,
+    "%{quote_include_paths}": ALL_COMPILE_ACTIONS,
+    "%{system_include_paths}": ALL_COMPILE_ACTIONS,
+    "%{preprocessor_defines}": ALL_COMPILE_ACTIONS,
+    "%{striptopts}": ACTION_NAMES.strip,
+    "%{legacy_compile_flags}": ALL_COMPILE_ACTIONS,
+    "%{user_compile_flags}": ALL_COMPILE_ACTIONS,
+    "%{unfiltered_compile_flags}": ALL_COMPILE_ACTIONS,
+    "%{runtime_library_search_directories}": ALL_LINK_ACTIONS,
+    "%{library_search_directories}": ALL_LINK_ACTIONS,
+    "%{libraries_to_link}": ALL_LINK_ACTIONS,
+    "%{legacy_link_flags}": ALL_LINK_ACTIONS,
+    "%{user_link_flags}": ALL_LINK_ACTIONS,
+    "%{linkstamp_flags}": ALL_LINK_ACTIONS,
+}
 
 def action_mux(action_map):
     """ Expands an iterable set of actions that map to a given flag. 
@@ -19,6 +87,46 @@ def action_mux(action_map):
             action_flags[action] = action_flags.get(action, []) + flags
     return action_flags
 
+BUILD_VARS_DOC_URL = "https://bazel.build/docs/cc-toolchain-config-reference"
+
+def _extract_build_var_from_flag(flag):
+    var_start_index = flag.find("%{")
+    if var_start_index == -1:
+        return None
+    var_end_index = flag.find("}", start = var_start_index)
+    if var_end_index == -1:
+        fail(
+            "In flag '%s' opening variable '%{' was found but got to \
+            end of flag and no closing bracket found '}'" % (flag),
+        )
+    else:
+        allowed_in_variable = list("abcdefghijklmnopqrstuvwxyz_".elems())
+        flag_name = flag[var_start_index + 2:var_end_index]
+        for c in flag_name.elems():
+            if c not in allowed_in_variable:
+                fail(
+                    "Found invalid character: ",
+                    c,
+                    " in variable.",
+                    " The following characters are supported:\n",
+                    allowed_in_variable,
+                    "See the docs for more information: ",
+                    BUILD_VARS_DOC_URL,
+                )
+
+        return flag[var_start_index:var_end_index + 1]
+
+def _validate_build_var_with_action(build_var, action, is_iterated = False):
+    if is_iterated:
+        if build_var not in FLAG_SEQUENCE_VARS.keys():
+            fail("Build var '%s' is not found or is not a sequence" % build_var)
+    else:
+        valid_actions = FLAG_VARS.get(build_var)
+        if not valid_actions:
+            fail("Build var '%s' is not found or is a sequence, and requires iteration" % build_var)
+        if action not in valid_actions:
+            fail("Build var is used with unsupported action '%s', the following actions are supported for this build var:\n %s" % (action, valid_actions))
+
 def _action_flags_as_flag_set(action, flags):
     return flag_set(
         actions = [action],
@@ -27,18 +135,22 @@ def _action_flags_as_flag_set(action, flags):
 
 def _cc_feature_impl(ctx):
     runfiles = ctx.runfiles(files = [])
+    feature_deps = []
     for dep in ctx.attr.deps:
         runfiles.merge(dep[DefaultInfo].default_runfiles)
+        if FeatureSetInfo in dep:
+            feature_deps.extend(dep[FeatureSetInfo].features)
 
+    this_feature = feature(
+        name = str(ctx.label),
+        enabled = ctx.attr.enabled,
+        flag_sets = [
+            _action_flags_as_flag_set(action, flags)
+            for action, flags in ctx.attr.action_flags.items()
+        ],
+    )
     return [
-        feature(
-            name = str(ctx.label),
-            enabled = ctx.attr.enabled,
-            flag_sets = [
-                _action_flags_as_flag_set(action, flags)
-                for action, flags in ctx.attr.action_flags.items()
-            ],
-        ),
+        feature_set(features = feature_deps + [this_feature]),
         DefaultInfo(
             files = depset(transitive = [
                 dep[DefaultInfo].files
@@ -64,8 +176,11 @@ cc_feature = rule(
         "deps": attr.label_list(
             doc = "The set of features that this feature implicitly enables/implies.",
         ),
+        "iterative_over_build_var": attr.string(
+            doc = "Iterate over a build variable"
+        )
     },
-    provides = [FeatureInfo],
+    provides = [FeatureSetInfo],
     doc = """
 Configure a pipeline through each action in the C++ build.
 

cc/toolchain.bzl

@@ -0,0 +1,77 @@
+load("@rules_cc//cc:cc_toolchain_config_lib.bzl", "FeatureSetInfo", "tool_path")
+
+# We are going to use action_confgs for everything as an alternative to
+# using tool_paths which just add unneccesary confusion.
+_NULL_TOOL_PATHS = [
+    tool_path(
+        name = "gcc",
+        path = "/usr/bin/clang",
+    ),
+    tool_path(
+        name = "ld",
+        path = "/usr/bin/ld",
+    ),
+    tool_path(
+        name = "ar",
+        path = "/bin/false",
+    ),
+    tool_path(
+        name = "cpp",
+        path = "/bin/false",
+    ),
+    tool_path(
+        name = "gcov",
+        path = "/bin/false",
+    ),
+    tool_path(
+        name = "nm",
+        path = "/bin/false",
+    ),
+    tool_path(
+        name = "objdump",
+        path = "/bin/false",
+    ),
+    tool_path(
+        name = "strip",
+        path = "/bin/false",
+    ),
+]
+
+def _toolchain_config_impl(ctx):
+    features = []
+    for feature in ctx.attr.features:
+        features.extend(feature[FeatureSetInfo].features)
+
+    return cc_common.create_cc_toolchain_config_info(
+        ctx = ctx,
+        features = features,  # NEW
+        # Unused let features handle this.
+        cxx_builtin_include_directories = [],
+        tool_paths = _NULL_TOOL_PATHS,
+
+        # TODO: Do we actually need any of these?
+        toolchain_identifier = "local",
+        host_system_name = "local",
+        target_system_name = "local",
+        target_cpu = "unknown",
+        target_libc = "unknown",
+        compiler = "unknown",
+        abi_version = "unknown",
+        abi_libc_version = "unknown",
+    )
+
+cc_toolchain_config = rule(
+    _toolchain_config_impl,
+    attrs = {
+        "cc_features": attr.label_list(
+            doc = "The list of cc_features to include in this toolchain.",
+            mandatory = True,
+            providers = [FeatureSetInfo],
+        ),
+        "action_configs": attr.label_list(
+            doc = "The list of cc_action_configs to include in this toolchain.",
+            mandatory = True,
+        ),
+    },
+    provides = [CcToolchainConfigInfo],
+)

third_party/clang_llvm_x86_64_linux_gnu_ubuntu.BUILD

@@ -1,6 +1,46 @@
+load("@bazel_skylib//rules:native_binary.bzl", "native_binary")
+package(default_visibility = ["//visibility:public"])
+
 exports_files(glob(["**/*"]))
 
 filegroup(
     name = "all_files",
     srcs = glob(["**/*"]),
 )
+
+TOOLS = {
+    "cxx": {
+        "tool": "//:bin/clang++",
+        "data": ["//:cc"],
+    },
+    "cc": {
+        "tool": "//:bin/clang",
+        "data": ["//:ld"],
+    },
+    "ld": {
+        "tool": "//:bin/ld.lld",
+        "data": [],
+    },
+    "ar": {
+        "tool": "//:bin/llvm-ar",
+        "data": [],
+    },
+    "objdump": {
+        "tool": "//:bin/llvm-objdump",
+        "data": [],
+    },
+    "strip": {
+        "tool": "//:bin/llvm-strip",
+        "data": [],
+    },
+}
+
+[
+    native_binary(
+        name = name,
+        src = info["tool"],
+        data = info["data"],
+        out = name,
+    )
+    for name, info in TOOLS.items()
+]