First step towards using bzlmod

 * Move projects that are available already in https://registry.bazel.build/
   from from load_external to MODULE.bazel.
 * This is not complete: there are probably more steps to simplify and
   clean-up after the first submit.
 * Switching to bzlmod broke making the compilation-db as the action hooks
   don't seem to work anymore ( xls/dev_tools//make-compilation-db.sh ).
   The used com_grail_bazel_compdb is not maintained anymore, so this needs
   to be updated to something more modern (hedronvision?).
   Since this is not actively needed in daily development (and I am the only
   one really using it), postponed for later.
 * Clean out things not needed anymore in dependency_support/$(various-dirs)

Issues: google#931

Also, needed to make Python rules to work well with
--incompatible_default_to_explicit_init_py (bazelbuild/bazel#10076)

.bazelrc

@@ -1,10 +1,14 @@
-# We use bazel >= 6, but no bzlmod yet.
-common --noenable_bzlmod
+common --enable_bzlmod
 
 # Disable rules_python Starlark rules for Bazel 7+.
 # See https://github.com/bazelbuild/rules_python/issues/1069#issuecomment-1942053014.
 build --action_env=RULES_PYTHON_ENABLE_PYSTAR=0
 
+# Disable automatic generation of __init__.py files. This allows
+# namespace packages (such as `google`) to work correctly.
+# https://github.com/bazelbuild/bazel/issues/10076
+build --incompatible_default_to_explicit_init_py=true
+
 # Minimium c++ standard used.
 build --cxxopt "-std=c++20"            --host_cxxopt "-std=c++20"
 build --action_env=BAZEL_CXXOPTS=-std=c++20

.gitignore

@@ -7,3 +7,4 @@ xls_clang-tidy.out
 user.bazelrc
 .vscode
 .cache
+MODULE.bazel.lock

MODULE.bazel

@@ -0,0 +1,38 @@
+module(
+    name = "xls",
+    repo_name = "com_google_xls",
+)
+
+# Compiler toolchain
+bazel_dep(name = "toolchains_llvm", version = "1.1.2")
+
+# Configure and register the toolchain.
+llvm = use_extension("@toolchains_llvm//toolchain/extensions:llvm.bzl", "llvm")
+llvm.toolchain(
+    llvm_version = "17.0.6",
+)
+use_repo(llvm, "llvm_toolchain")
+
+register_toolchains("@llvm_toolchain//:all")
+
+#
+bazel_dep(name = "abseil-cpp", version = "20240116.2", repo_name = "com_google_absl")
+bazel_dep(name = "abseil-py", version = "2.1.0", repo_name = "com_google_absl_py")
+bazel_dep(name = "bazel_skylib", version = "1.7.1")
+bazel_dep(name = "boringssl", version = "0.0.0-20240530-2db0eb3")
+bazel_dep(name = "google_benchmark", version = "1.8.5", repo_name = "com_google_benchmark")
+bazel_dep(name = "googleapis", version = "0.0.0-20240326-1c8d509c5", repo_name = "com_google_googleapis")
+bazel_dep(name = "googletest", version = "1.15.2", repo_name = "com_google_googletest")
+bazel_dep(name = "grpc", version = "1.66.0", repo_name = "com_github_grpc_grpc")
+bazel_dep(name = "nlohmann_json", version = "3.11.3", repo_name = "jsonhpp")
+bazel_dep(name = "protobuf", version = "28.0-rc2", repo_name = "com_google_protobuf")
+bazel_dep(name = "re2", version = "2024-07-02", repo_name = "com_googlesource_code_re2")
+bazel_dep(name = "riegeli", version = "0.0.0-20240606-973b6f0", repo_name = "com_google_riegeli")
+bazel_dep(name = "rules_cc", version = "0.0.9")
+bazel_dep(name = "rules_license", version = "0.0.8")
+bazel_dep(name = "rules_pkg", version = "1.0.1")
+
+# Not all external projects we directly need are available yet.
+# This how to find what we use for further work on this file:
+#   find xls -name BUILD -o -name "*.bzl" | xargs sed 's/.*"\(@[_a-z0-9]*\).*/\1/p;d' | sort -u
+# Once added here, remove from the {load,initialize}_external.bzl.

WORKSPACE

@@ -12,46 +12,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# TODO(#931): Everything here should go away and migrate to MODULE.bazel
+
 workspace(name = "com_google_xls")
 
-# Load and configure a hermetic LLVM based C/C++ toolchain. This is done here
-# and not in load_external.bzl because it requires several sequential steps of
-# declaring archives and using things in them, which is awkward to do in .bzl
-# files because it's not allowed to use `load` inside of a function.
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
-# Released 2023-09-20, current as of 2024-06-26 (but there is already a 0.0.10rc1)
-# Needs to be loaded first, as llvm toolchain has an ancient version of this.
-http_archive(
-    name = "rules_cc",
-    urls = ["https://github.com/bazelbuild/rules_cc/releases/download/0.0.9/rules_cc-0.0.9.tar.gz"],
-    sha256 = "2037875b9a4456dce4a79d112a8ae885bbc4aad968e6587dca6e64f3a0900cdf",
-    strip_prefix = "rules_cc-0.0.9",
-)
-
-# Commit on  2024-07-19, current as of 2024-07-21.
-http_archive(
-    name = "toolchains_llvm",
-    integrity = "sha256-RVp0bZsDrelQAtxswWOLB4j8zCXQy/cSe1m3wL/E2PU=",
-    strip_prefix = "toolchains_llvm-01132cfdae7d7187a885cf79d5a3ac1ed8a02e5a",
-    url = "https://github.com/bazel-contrib/toolchains_llvm/archive/01132cfdae7d7187a885cf79d5a3ac1ed8a02e5a.tar.gz",
-)
-
-load("@toolchains_llvm//toolchain:deps.bzl", "bazel_toolchain_dependencies")
-
-bazel_toolchain_dependencies()
-
-load("@toolchains_llvm//toolchain:rules.bzl", "llvm_toolchain")
-
-llvm_toolchain(
-    name = "llvm_toolchain",
-    llvm_version = "17.0.6",
-)
-
-load("@llvm_toolchain//:toolchains.bzl", "llvm_register_toolchains")
-
-llvm_register_toolchains()
-
 load("//dependency_support:load_external.bzl", "load_external_repositories")
 
 load_external_repositories()
@@ -75,22 +41,10 @@ python_register_toolchains(
     ignore_root_user_error = True,
 )
 
-# gRPC deps should be loaded before initializing other repos. Otherwise, various
-# errors occur during repo loading and initialization.
-load("@com_github_grpc_grpc//bazel:grpc_deps.bzl", "grpc_deps")
-
-grpc_deps()
-
 load("//dependency_support:initialize_external.bzl", "initialize_external_repositories")
 
 initialize_external_repositories()
 
 load("@xls_pip_deps//:requirements.bzl", xls_pip_install_deps = "install_deps")
 
 xls_pip_install_deps()
-
-# Loading the extra deps must be called after initialize_eternal_repositories or
-# the call to pip_parse fails.
-load("@com_github_grpc_grpc//bazel:grpc_extra_deps.bzl", "grpc_extra_deps")
-
-grpc_extra_deps()

dependency_support/initialize_external.bzl

@@ -14,10 +14,9 @@
 
 """Provides helper that initializes external repositories with third-party code."""
 
-load("@bazel_skylib//:workspace.bzl", "bazel_skylib_workspace")
-load("@com_google_benchmark//:bazel/benchmark_deps.bzl", "benchmark_deps")
-load("@com_google_protobuf//:protobuf_deps.bzl", "protobuf_deps")
-load("@com_grail_bazel_compdb//:deps.bzl", "bazel_compdb_deps")
+# TODO(#931): with MODULE.bazel, probably some of these can be removed now, with the
+# eventual goal that none of this is needed anymore and the file can be removed.
+
 load("@io_bazel_rules_closure//closure:repositories.bzl", "rules_closure_dependencies", "rules_closure_toolchains")
 load("@project_python//:defs.bzl", python_interpreter_target = "interpreter")
 load("@rules_7zip//:setup.bzl", "setup_7zip")  # needed by rules_hdl
@@ -31,8 +30,6 @@ load("//dependency_support/llvm:initialize.bzl", initialize_llvm = "initialize")
 
 def initialize_external_repositories():
     """Calls set-up methods for external repositories that require that."""
-    bazel_skylib_workspace()
-    protobuf_deps()
     rules_hdl_init(python_interpreter_target = python_interpreter_target)
     rules_hdl_dependency_support()
     setup_7zip()
@@ -48,6 +45,4 @@ def initialize_external_repositories():
     )
     initialize_boost()
     initialize_llvm()
-    bazel_compdb_deps()
-    benchmark_deps()
     rules_pkg_dependencies()