Add a repository rule for efficient sysroots

MODULE.bazel

@@ -21,9 +21,22 @@ module(
 
 bazel_dep(name = "bazel_features", version = "1.36.0")
 bazel_dep(name = "bazel_skylib", version = "1.5.0")
+bazel_dep(name = "aspect_bazel_lib", version = "2.0.0")
 bazel_dep(name = "rules_cc", version = "0.2.2")
 bazel_dep(name = "platforms", version = "0.0.8")
 bazel_dep(name = "helly25_bzl", version = "0.1.2")
 
+bazel_dep(name = "tar.bzl", version = "0.6.0")
+tar_toolchains = use_extension("@tar.bzl//tar:extensions.bzl", "toolchains")
+use_repo(
+    tar_toolchains,
+    "bsd_tar_toolchains_darwin_amd64",
+    "bsd_tar_toolchains_darwin_arm64",
+    "bsd_tar_toolchains_linux_amd64",
+    "bsd_tar_toolchains_linux_arm64",
+    "bsd_tar_toolchains_windows_amd64",
+    "bsd_tar_toolchains_windows_arm64",
+)
+
 # TODO: Remove when protobuf is released with a version of rules_python that supports 8.x
 bazel_dep(name = "rules_python", version = "1.0.0", dev_dependency = True)

tests/MODULE.bazel

@@ -171,7 +171,7 @@ llvm.toolchain_root(
 )
 llvm.sysroot(
     name = "llvm_toolchain_with_sysroot",
-    label = "@org_chromium_sysroot_linux_x64//:sysroot",
+    label = "@org_chromium_sysroot_linux_x64//sysroot",
     targets = ["linux-x86_64"],
 )
 use_repo(llvm, "llvm_toolchain_with_sysroot")
@@ -253,18 +253,11 @@ libclang_rt_wasm32 = use_repo_rule("//wasm:wasi_sdk.bzl", "libclang_rt_wasm32")
 
 libclang_rt_wasm32(name = "libclang_rt_wasm32")
 
-http_archive = use_repo_rule("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+sysroot = use_repo_rule("@toolchains_llvm//toolchain:sysroot.bzl", "sysroot")
 
 # This sysroot is used by github.com/vsco/bazel-toolchains.
-http_archive(
+sysroot(
     name = "org_chromium_sysroot_linux_x64",
-    build_file_content = """
-filegroup(
-  name = "sysroot",
-  srcs = glob(["*/**"]),
-  visibility = ["//visibility:public"],
-)
-""",
     sha256 = "84656a6df544ecef62169cfe3ab6e41bb4346a62d3ba2a045dc5a0a2ecea94a3",
     urls = ["https://commondatastorage.googleapis.com/chrome-linux-sysroot/toolchain/2202c161310ffde63729f29d27fe7bb24a0bc540/debian_stretch_amd64_sysroot.tar.xz"],
 )

tests/WORKSPACE

@@ -20,6 +20,25 @@ local_repository(
 )
 
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+http_archive(
+    name = "aspect_bazel_lib",
+    sha256 = "c4f36285ceed51f75da44ffcf8fa393794d0dc2e273a2e03be50462e347740cd",
+    strip_prefix = "bazel-lib-2.0.0",
+    url = "https://github.com/aspect-build/bazel-lib/releases/download/v2.0.0/bazel-lib-v2.0.0.tar.gz",
+)
+
+http_archive(
+    name = "tar.bzl",
+    sha256 = "a147d473a359742db2a43c8a9a8e04e31321582e6bb669dafc5ba6b2c59845d1",
+    strip_prefix = "tar.bzl-0.6.0",
+    url = "https://github.com/bazel-contrib/tar.bzl/releases/download/v0.6.0/tar.bzl-v0.6.0.tar.gz",
+)
+
+load("@tar.bzl//tar:extensions.bzl", "create_repositories")
+
+create_repositories()
+
 load("@toolchains_llvm//toolchain:deps.bzl", "bazel_toolchain_dependencies")
 
 bazel_toolchain_dependencies()
@@ -114,15 +133,10 @@ llvm_toolchain(
 ## Toolchain example with a sysroot.
 
 # This sysroot is used by github.com/vsco/bazel-toolchains.
-http_archive(
+load("@toolchains_llvm//toolchain:sysroot.bzl", "sysroot")
+
+sysroot(
     name = "org_chromium_sysroot_linux_x64",
-    build_file_content = """
-filegroup(
-  name = "sysroot",
-  srcs = glob(["*/**"]),
-  visibility = ["//visibility:public"],
-)
-""",
     sha256 = "84656a6df544ecef62169cfe3ab6e41bb4346a62d3ba2a045dc5a0a2ecea94a3",
     urls = ["https://commondatastorage.googleapis.com/chrome-linux-sysroot/toolchain/2202c161310ffde63729f29d27fe7bb24a0bc540/debian_stretch_amd64_sysroot.tar.xz"],
 )
@@ -131,7 +145,7 @@ llvm_toolchain(
     name = "llvm_toolchain_with_sysroot",
     llvm_versions = LLVM_VERSIONS,
     sysroot = {
-        "linux-x86_64": "@org_chromium_sysroot_linux_x64//:sysroot",
+        "linux-x86_64": "@org_chromium_sysroot_linux_x64//sysroot",
     },
     # We can share the downloaded LLVM distribution with the first configuration.
     toolchain_roots = {

toolchain/internal/configure.bzl

@@ -320,7 +320,7 @@ def _cc_toolchain_str(
     sysroot_path = toolchain_info.sysroot_paths_dict.get(target_pair)
     sysroot_label = toolchain_info.sysroot_labels_dict.get(target_pair)
     if sysroot_label:
-        sysroot_label_str = "\"%s\"" % str(sysroot_label)
+        sysroot_label_str = repr(str(sysroot_label))
     else:
         sysroot_label_str = ""
 
@@ -466,6 +466,11 @@ filegroup(
 
     if use_absolute_paths_llvm:
         template = template + """
+filegroup(
+    name = "cxx_builtin_include_files-{suffix}",
+    srcs = [],
+)
+
 filegroup(
     name = "compiler-components-{suffix}",
     srcs = [
@@ -499,10 +504,17 @@ filegroup(name = "strip-files-{suffix}", srcs = [{extra_files_str}])
     else:
         template = template + """
 filegroup(
-    name = "compiler-components-{suffix}",
+    name = "cxx_builtin_include_files-{suffix}",
     srcs = [
         "{llvm_dist_label_prefix}clang",
         "{llvm_dist_label_prefix}include",
+    ],
+)
+
+filegroup(
+    name = "compiler-components-{suffix}",
+    srcs = [
+        ":cxx_builtin_include_files-{suffix}",
         ":sysroot-components-{suffix}",
         {extra_compiler_files}
     ],
@@ -539,18 +551,11 @@ filegroup(name = "strip-files-{suffix}", srcs = ["{llvm_dist_label_prefix}strip"
 """
 
     template = template + """
-filegroup(
-    name = "include-components-{suffix}",
-    srcs = [
-        ":compiler-components-{suffix}",
-        ":sysroot-components-{suffix}",
-    ],
-)
-
 system_module_map(
     name = "module-{suffix}",
-    cxx_builtin_include_files = ":include-components-{suffix}",
+    cxx_builtin_include_files = ":cxx_builtin_include_files-{suffix}",
     cxx_builtin_include_directories = {cxx_builtin_include_directories},
+    sysroot_files = ":sysroot-components-{suffix}",
     sysroot_path = "{sysroot_path}",
 )
 

toolchain/internal/system_module_map.bzl

@@ -57,12 +57,28 @@ def _system_module_map(ctx):
 
     template_dict = ctx.actions.template_dict()
     template_dict.add_joined(
-        "%textual_headers%",
+        "%cxx_builtin_include_files%",
         ctx.attr.cxx_builtin_include_files[DefaultInfo].files,
         join_with = "\n",
         map_each = textual_header_closure,
         allow_closure = True,
     )
+
+    # We don't have a good way to detect a source directory, so check if it's a single File...
+    sysroot_files = ctx.attr.sysroot_files[DefaultInfo].files.to_list()
+    if len(sysroot_files) == 1:
+        path = paths.normalize(sysroot_files[0].path).replace("//", "/")
+        template_dict.add("%sysroot%", _umbrella_submodule(execroot_prefix + path))
+    else:
+        print("WARNING: Sysroot {} did not resolve to a single (directory) file. Consider using the `sysroot` repository rule in @toolchains_llvm//toolchain:sysroot.bzl for more efficient builds.".format(ctx.attr.sysroot_files.label))  # buildifier: disable=print
+        template_dict.add_joined(
+            "%sysroot%",
+            ctx.attr.sysroot_files[DefaultInfo].files,
+            join_with = "\n",
+            map_each = textual_header_closure,
+            allow_closure = True,
+        )
+
     template_dict.add_joined(
         "%umbrella_submodules%",
         depset(absolute_path_dirs),
@@ -87,6 +103,7 @@ system_module_map = rule(
     attrs = {
         "cxx_builtin_include_files": attr.label(mandatory = True),
         "cxx_builtin_include_directories": attr.string_list(mandatory = True),
+        "sysroot_files": attr.label(),
         "sysroot_path": attr.string(),
         "_module_map_template": attr.label(
             default = "template.modulemap",

toolchain/internal/template.modulemap

@@ -1,4 +1,5 @@
 module "crosstool" [system] {
-%textual_headers%
+%cxx_builtin_include_files%
+%sysroot%
 %umbrella_submodules%
 }

toolchain/sysroot.bzl

@@ -0,0 +1,70 @@
+load("@aspect_bazel_lib//lib:repo_utils.bzl", "repo_utils")
+
+def _sysroot_impl(rctx):
+    urls = rctx.attr.urls
+    if rctx.attr.url:
+        urls = [rctx.attr.url] + urls
+
+    if not urls:
+        fail("At least one of url and urls must be provided")
+
+    _, _, archive = urls[0].rpartition("/")
+
+    rctx.download(urls, archive, sha256 = rctx.attr.sha256)
+
+    # Source directories are more efficient than file groups for 2 reasons:
+    #   - They can be symlinked into a local sandbox with a single symlink instead of 1-per-file
+    #   - They serve as a signal to the Merkle tree cache machinery since they can be memoized as a single node.
+    # Since sysroots are usually a ton of files, it can improve build performance to declare them as source directories.
+
+    # Also, create the BUILD file before extracting because `bsdtar` expects the target
+    # directory to exist, and this way Bazel creates it for us without needing `mkdir`.
+    rctx.file(
+        "sysroot/BUILD.bazel",
+        """filegroup(
+    name = "sysroot",
+    srcs = ["."],
+    visibility = ["//visibility:public"],
+)""",
+    )
+
+    host_bsdtar = Label("@bsd_tar_toolchains_%s//:tar" % repo_utils.platform(rctx))
+
+    cmd = [
+        str(rctx.path(host_bsdtar)),
+        "--extract",
+        "--no-same-owner",
+        "--no-same-permissions",
+        "--file",
+        archive,
+        "--directory",
+        "sysroot",
+    ]
+
+    for include in rctx.attr.include_patterns:
+        cmd.extend(["--include", include])
+
+    for exclude in rctx.attr.exclude_patterns:
+        cmd.extend(["--exclude", exclude])
+
+    result = rctx.execute(cmd)
+    if result.return_code != 0:
+        fail(result.stdout + result.stderr)
+
+    rctx.delete(archive)
+
+    if hasattr(rctx, "repo_metadata"):
+        return rctx.repo_metadata(reproducible = True)
+    else:
+        return None
+
+sysroot = repository_rule(
+    implementation = _sysroot_impl,
+    attrs = {
+        "url": attr.string(),
+        "urls": attr.string_list(),
+        "sha256": attr.string(),
+        "include_patterns": attr.string_list(),
+        "exclude_patterns": attr.string_list(),
+    },
+)