feat: Migrate to bzlmod

.github/workflows/.bazelrc.ci

@@ -16,3 +16,6 @@
 
 common --keep_going
 common --remote_upload_local_results
+
+common:bzlmod --enable_bzlmod
+common:workspace --noenable_bzlmod

.github/workflows/default.yaml

@@ -22,6 +22,9 @@ jobs:
         os:
           - ubuntu-22.04
           - ubuntu-24.04
+        bzlmod_config:
+          - bzlmod
+          - workspace
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
@@ -35,14 +38,17 @@ jobs:
       - name: Test
         run: |
           ln -s .github/workflows/.bazelrc.ci .bazelrc.ci
-          bazel test //...
+          bazel test --config ${{ matrix.bzlmod_config }} //...
   compilation_modes:
     strategy:
       matrix:
         compilation_mode:
           - fastbuild
           - dbg
           - opt
+        bzlmod_config:
+          - bzlmod
+          - workspace
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
@@ -56,7 +62,7 @@ jobs:
       - name: Test
         run: |
           ln -s .github/workflows/.bazelrc.ci .bazelrc.ci
-          bazel test --compilation_mode ${{ matrix.compilation_mode }} //...
+          bazel test --compilation_mode ${{ matrix.compilation_mode }} --config ${{ matrix.bzlmod_config }} //...
   sanitizers:
     strategy:
       matrix:
@@ -65,6 +71,9 @@ jobs:
           - lsan
           - tsan
           - ubsan
+        bzlmod_config:
+          - bzlmod
+          - workspace
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
@@ -78,8 +87,13 @@ jobs:
       - name: Test ${{ matrix.sanitizer }}
         run: |
           ln -s .github/workflows/.bazelrc.ci .bazelrc.ci
-          bazel test --config ${{ matrix.sanitizer }} //tests/sanitizers:${{ matrix.sanitizer }}_test
+          bazel test --config ${{ matrix.sanitizer }} --config ${{ matrix.bzlmod_config }} //tests/sanitizers:${{ matrix.sanitizer }}_test
   coverage:
+    strategy:
+      matrix:
+        bzlmod_config:
+          - bzlmod
+          - workspace
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
@@ -93,13 +107,16 @@ jobs:
       - name: Test Coverage
         run: |
           ln -s .github/workflows/.bazelrc.ci .bazelrc.ci
-          bazel coverage //examples/hello_world_cpp:hello_world_cpp_test
+          bazel coverage --config ${{ matrix.bzlmod_config }} //examples/hello_world_cpp:hello_world_cpp_test
   rbe:
     strategy:
       matrix:
         os:
           - ubuntu-22.04
           - macos-14
+        bzlmod_config:
+          - bzlmod
+          - workspace
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
@@ -113,4 +130,4 @@ jobs:
       - name: Test with RBE
         run: |
           ln -s .github/workflows/.bazelrc.ci .bazelrc.ci
-          bazel test --config rbe //...
+          bazel test --config rbe --config ${{ matrix.bzlmod_config }} //...

MODULE.bazel

@@ -0,0 +1,64 @@
+module(name = "gcc_toolchain")
+
+# Dependencies
+# ============
+bazel_dep(name = "bazel_skylib", version = "1.8.1")
+bazel_dep(name = "aspect_bazel_lib", version = "1.40.2")
+bazel_dep(name = "platforms", version = "1.0.0")
+bazel_dep(name = "rules_cc", version = "0.2.0")
+
+# Local Toolchains
+# ================
+gcc_toolchains = use_extension("//toolchain:module_extensions.bzl", "gcc_toolchains", dev_dependency = True)
+
+[
+    [
+        gcc_toolchains.toolchain(
+            name = "gcc_toolchain_{}".format(arch),
+            target_arch = arch,
+        ),
+        use_repo(gcc_toolchains, "gcc_toolchain_{}".format(arch)),
+        register_toolchains(
+            "@gcc_toolchain_{}//:cc_toolchain".format(arch),
+            "@gcc_toolchain_{}//:fortran_toolchain".format(arch),
+            # Register toolchains as dev dependencies so that we don't pollute the toolchain resolution of consumers.
+            dev_dependency = True,
+        ),
+    ]
+    # Unfortunately, we can't load `ARCHS` directly here.
+    # But the attributes in `gcc_toolchains.toolchain` are gated to only contain values from ARCHS.
+    for arch in [
+        "aarch64",
+        "armv7",
+        "x86_64",
+    ]
+]
+
+# Dev Dependencies (for examples/)
+# ===============================
+bazel_dep(name = "rules_proto", version = "7.1.0", dev_dependency = True)
+bazel_dep(name = "rules_foreign_cc", version = "0.15.0", dev_dependency = True)
+bazel_dep(name = "stardoc", version = "0.5.6", dev_dependency = True, repo_name = "io_bazel_stardoc")
+# We pin stardoc because a dependency requests a newer version (0.7.2), but the non-workspace flow doesn't work with it.
+single_version_override(
+    module_name = "stardoc",
+    version = "0.5.6",
+)
+
+bazel_dep(name = "protobuf", version = "29.3", dev_dependency = True, repo_name = "com_google_protobuf")
+single_version_override(
+    module_name = "protobuf",
+    patch_strip = 1,
+    patches = [
+        "//third_party/patches:com_google_protobuf.bzlmod.patch",
+    ],
+    version = "29.3",
+)
+
+non_bazel_dependencies = use_extension("//:internal.bzl", "non_bazel_dependencies")
+use_repo(
+    non_bazel_dependencies,
+    "avl",
+    "lapack",
+    "openssl",
+)

examples/lapack/BUILD.bazel

@@ -16,6 +16,7 @@
 # limitations under the License.
 
 load("@rules_foreign_cc//foreign_cc:make.bzl", "make")
+load(":patches.bzl", "lapack_repo_name")
 
 _libs = [
     "liblapack.a",
@@ -43,7 +44,10 @@ make(
     lib_source = "@lapack//:srcs",
     out_static_libs = _libs,
     postfix_script = "\n".join([
-        "mv $$EXT_BUILD_ROOT/external/lapack/{0} $$INSTALLDIR/lib/{0}".format(lib)
+        "mv $$EXT_BUILD_ROOT/external/{0}/{1} $$INSTALLDIR/lib/{1}".format(
+            lapack_repo_name,
+            lib,
+        )
         for lib in _libs
     ]),
     targets = [

examples/lapack/patches.bzl

@@ -55,3 +55,7 @@ EOF
 """
 
 LAPACK_PATCHES = [_create_make_inc]
+
+# Canonical repository name of the @lapack dependency.
+# Documentation: https://bazel.build/external/module#repository_names_and_strict_deps
+lapack_repo_name = Label("@lapack").repo_name

internal.bzl

@@ -18,9 +18,36 @@
 """Internal dependencies the users don't need."""
 
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
-
 load("//examples/lapack:patches.bzl", "LAPACK_PATCHES")
 
+def _openssl():
+    http_archive(
+        name = "openssl",
+        build_file_content = _ALL_SRCS,
+        sha256 = "40dceb51a4f6a5275bde0e6bf20ef4b91bfc32ed57c0552e2e8e15463372b17a",
+        strip_prefix = "openssl-1.1.1n",
+        url = "https://www.openssl.org/source/openssl-1.1.1n.tar.gz",
+    )
+
+def _lapack():
+    http_archive(
+        name = "lapack",
+        build_file_content = _ALL_SRCS,
+        patch_cmds = LAPACK_PATCHES,
+        sha256 = "eac9570f8e0ad6f30ce4b963f4f033f0f643e7c3912fc9ee6cd99120675ad48b",
+        strip_prefix = "lapack-3.12.0",
+        url = "https://github.com/Reference-LAPACK/lapack/archive/refs/tags/v3.12.0.tar.gz",
+    )
+
+def _avl():
+    http_archive(
+        name = "avl",
+        build_file = "@//:examples/avl/avl.BUILD.bazel",
+        sha256 = "6d62e563578b79795a84958cfe4e221a4c9847fbeb4a821d45bc049934fc6a90",
+        strip_prefix = "Avl",
+        url = "https://web.mit.edu/drela/Public/web/avl/avl3.40b.tgz",
+    )
+
 # buildifier: disable=function-docstring
 def internal_dependencies():
     http_archive(
@@ -53,30 +80,8 @@ def internal_dependencies():
         url = "https://github.com/bazel-contrib/rules_python/releases/download/1.4.1/rules_python-1.4.1.tar.gz",
     )
 
-    http_archive(
-        name = "openssl",
-        build_file_content = _ALL_SRCS,
-        sha256 = "40dceb51a4f6a5275bde0e6bf20ef4b91bfc32ed57c0552e2e8e15463372b17a",
-        strip_prefix = "openssl-1.1.1n",
-        url = "https://www.openssl.org/source/openssl-1.1.1n.tar.gz",
-    )
-
-    http_archive(
-        name = "lapack",
-        build_file_content = _ALL_SRCS,
-        patch_cmds = LAPACK_PATCHES,
-        sha256 = "eac9570f8e0ad6f30ce4b963f4f033f0f643e7c3912fc9ee6cd99120675ad48b",
-        strip_prefix = "lapack-3.12.0",
-        url = "https://github.com/Reference-LAPACK/lapack/archive/refs/tags/v3.12.0.tar.gz",
-    )
-
-    http_archive(
-        name = "avl",
-        build_file = "@//:examples/avl/avl.BUILD.bazel",
-        sha256 = "6d62e563578b79795a84958cfe4e221a4c9847fbeb4a821d45bc049934fc6a90",
-        strip_prefix = "Avl",
-        url = "https://web.mit.edu/drela/Public/web/avl/avl3.40b.tgz",
-    )
+    _openssl()
+    _lapack()
 
     http_archive(
         name = "com_google_protobuf",
@@ -87,6 +92,8 @@ def internal_dependencies():
         url = "https://github.com/protocolbuffers/protobuf/releases/download/v29.3/protobuf-29.3.tar.gz",
     )
 
+    _avl()
+
     http_archive(
         name = "rules_pkg",
         sha256 = "b7215c636f22c1849f1c3142c72f4b954bb12bb8dcf3cbe229ae6e69cc6479db",
@@ -103,3 +110,12 @@ filegroup(
     visibility = ["//visibility:public"],
 )
 """
+
+def _non_bazel_dependencies_ext_impl(mctx):
+    _openssl()
+    _lapack()
+    _avl()
+
+non_bazel_dependencies = module_extension(
+    implementation = _non_bazel_dependencies_ext_impl,
+)

third_party/patches/com_google_protobuf.bzlmod.patch

@@ -0,0 +1,71 @@
+diff --git a/BUILD.bazel b/BUILD.bazel
+index 32b26cbdc..3b6026976 100644
+--- a/BUILD.bazel
++++ b/BUILD.bazel
+@@ -1,6 +1,6 @@
+ # Bazel (https://bazel.build/) BUILD file for Protobuf.
+
+-load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library")
++load("@gcc_toolchain//rules_cc:defs.bzl", "cc_binary", "cc_library")
+ load("@rules_license//rules:license.bzl", "license")
+ load("@rules_pkg//pkg:mappings.bzl", "pkg_files", "strip_prefix")
+ load("//bazel:cc_proto_library.bzl", "cc_proto_library")
+diff --git a/MODULE.bazel b/MODULE.bazel
+index cbe66f826..31fd30b9d 100644
+--- a/MODULE.bazel
++++ b/MODULE.bazel
+@@ -180,3 +180,15 @@ bazel_dep(
+     version = "4.0.0",
+     dev_dependency = True,
+ )
++
++# We load gcc_toolchain by the same name as we declare it in module().
++# Then, we use use_repo to bring the @gcc_toolchain_<arch> repositories into scope
++# so that we can reference them later when depending in libstdcxx
++bazel_dep(
++    name = "gcc_toolchain",
++    version = "0.0.0",
++)
++gcc_toolchains = use_extension("@gcc_toolchain//toolchain:module_extensions.bzl", "gcc_toolchains")
++use_repo(gcc_toolchains, "gcc_toolchain_aarch64")
++use_repo(gcc_toolchains, "gcc_toolchain_armv7")
++use_repo(gcc_toolchains, "gcc_toolchain_x86_64")
+diff --git a/conformance/BUILD.bazel b/conformance/BUILD.bazel
+index 9d7938d75..e8db19453 100644
+--- a/conformance/BUILD.bazel
++++ b/conformance/BUILD.bazel
+@@ -1,6 +1,7 @@
+ # Conformance testing for Protobuf.
+
+-load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library", "objc_library")
++load("@rules_cc//cc:defs.bzl", "objc_library")
++load("@gcc_toolchain//rules_cc:defs.bzl", "cc_binary", "cc_library")
+ load(
+     "@rules_pkg//pkg:mappings.bzl",
+     "pkg_filegroup",
+diff --git a/examples/BUILD.bazel b/examples/BUILD.bazel
+index 4b701c403..3f0c9acb7 100644
+--- a/examples/BUILD.bazel
++++ b/examples/BUILD.bazel
+@@ -9,7 +9,7 @@ load("@com_google_protobuf//bazel:java_lite_proto_library.bzl", "java_lite_proto
+ load("@com_google_protobuf//bazel:java_proto_library.bzl", "java_proto_library")
+ load("@com_google_protobuf//bazel:proto_library.bzl", "proto_library")
+ load("@com_google_protobuf//bazel:py_proto_library.bzl", "py_proto_library")
+-load("@rules_cc//cc:defs.bzl", "cc_binary")
++load("@gcc_toolchain//rules_cc:defs.bzl", "cc_binary")
+ load("@rules_pkg//pkg:mappings.bzl", "pkg_files", "strip_prefix")
+ load("@rules_python//python:py_binary.bzl", "py_binary")
+
+diff --git a/src/google/protobuf/compiler/BUILD.bazel b/src/google/protobuf/compiler/BUILD.bazel
+index 5012ee793..cac054e7b 100644
+--- a/src/google/protobuf/compiler/BUILD.bazel
++++ b/src/google/protobuf/compiler/BUILD.bazel
+@@ -2,7 +2,7 @@
+ # Protocol Buffers Compiler
+ ################################################################################
+
+-load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library", "cc_test")
++load("@gcc_toolchain//rules_cc:defs.bzl", "cc_binary", "cc_library", "cc_test")
+ load(
+     "@rules_pkg//pkg:mappings.bzl",
+     "pkg_attributes",