Introduce a Bazel build system

.bazelignore

@@ -0,0 +1,8 @@
+# Directories populated by the CMake build (FetchContent checkouts and the
+# third_party/absl symlink) contain their own BUILD files and must not be
+# treated as packages of this workspace.
+third_party/abseil-cpp
+third_party/absl
+third_party/benchmark
+build
+python

.bazelrc

@@ -0,0 +1,10 @@
+# SentencePiece requires C++17.
+build --enable_platform_specific_config
+
+build:linux --cxxopt=-std=c++17 --host_cxxopt=-std=c++17
+build:macos --cxxopt=-std=c++17 --host_cxxopt=-std=c++17
+build:freebsd --cxxopt=-std=c++17 --host_cxxopt=-std=c++17
+build:windows --cxxopt=/std:c++17 --host_cxxopt=/std:c++17
+build:windows --cxxopt=/utf-8 --host_cxxopt=/utf-8
+
+test --test_output=errors

.bazelversion

@@ -0,0 +1 @@
+9.1.1

.github/workflows/bazel.yml

@@ -0,0 +1,77 @@
+name: CI for Bazel build
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  build-and-test:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ ubuntu-latest, ubuntu-24.04-arm, macos-latest, windows-latest ]
+
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 60
+
+    env:
+      # Stop the MSYS bash on Windows from rewriting Bazel labels like
+      # //src:spm_test as filesystem paths.
+      MSYS_NO_PATHCONV: "1"
+      MSYS2_ARG_CONV_EXCL: "*"
+
+    steps:
+    - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+
+    - name: Mount Bazel caches
+      uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
+      with:
+        path: |
+          ~/.cache/bazel-disk
+          ~/.cache/bazel-repo
+        key: bazel-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('MODULE.bazel', '.bazelrc', '.bazelversion') }}
+        restore-keys: |
+          bazel-${{ runner.os }}-${{ runner.arch }}-
+
+    - name: Configure Bazel
+      shell: bash
+      run: |
+        home="$HOME"
+        if [[ "$RUNNER_OS" == "Windows" ]]; then
+          home="$(cygpath -m "$HOME")"
+          # Keep output paths short to stay within MAX_PATH limits.
+          echo "startup --output_user_root=C:/bzl" >> "$HOME/.bazelrc"
+          # Materialize the runfiles tree so tests can read their data
+          # dependencies from the working directory, as on Linux/macOS.
+          echo "build --enable_runfiles" >> "$HOME/.bazelrc"
+          if [[ -z "${BAZEL_SH:-}" ]]; then
+            echo 'BAZEL_SH=C:\Program Files\Git\bin\bash.exe' >> "$GITHUB_ENV"
+          fi
+        fi
+        echo "build --disk_cache=$home/.cache/bazel-disk" >> "$HOME/.bazelrc"
+        echo "build --repository_cache=$home/.cache/bazel-repo" >> "$HOME/.bazelrc"
+
+    - name: Build
+      shell: bash
+      run: bazel build --verbose_failures //...
+
+    - name: Test
+      shell: bash
+      run: bazel test //src:spm_test
+
+    - name: Smoke test
+      shell: bash
+      run: |
+        workdir="$PWD"
+        if [[ "$RUNNER_OS" == "Windows" ]]; then
+          workdir="$(cygpath -m "$PWD")"
+        fi
+        bazel run //src:spm_train -- \
+          --input="$workdir/data/botchan.txt" --model_prefix="$workdir/m" --vocab_size=1000
+        echo "Hello world." | bazel-bin/src/spm_encode --model="$workdir/m.model"

.gitignore

@@ -83,3 +83,7 @@ python/test/sp_*.pickle
 third_party/absl
 
 test_tmp
+
+# Bazel
+/bazel-*
+MODULE.bazel.lock

BUILD.bazel

@@ -0,0 +1,31 @@
+# Copyright 2018 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.!
+
+package(default_visibility = ["//visibility:public"])
+
+exports_files([
+    "VERSION.txt",
+    "config.h.in",
+    "LICENSE",
+])
+
+alias(
+    name = "sentencepiece",
+    actual = "//src:sentencepiece",
+)
+
+alias(
+    name = "sentencepiece_train",
+    actual = "//src:sentencepiece_train",
+)

CMakeLists.txt

@@ -193,21 +193,10 @@ if (SPM_ABSL_PROVIDER STREQUAL "module")
         GIT_PROGRESS TRUE
         GIT_TAG 20260526.0)
   add_subdirectory(third_party/abseil-cpp)
-  if (NOT EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/third_party/absl)
-    file(CREATE_LINK
-         ${CMAKE_CURRENT_SOURCE_DIR}/third_party/abseil-cpp/absl
-         ${CMAKE_CURRENT_SOURCE_DIR}/third_party/absl
-         SYMBOLIC)
-  endif()
+  include_directories(${CMAKE_CURRENT_SOURCE_DIR}/third_party/abseil-cpp)
 elseif (SPM_ABSL_PROVIDER STREQUAL "package")
   find_package(absl REQUIRED)
   get_target_property(ABSL_INCLUDE_DIRS absl::base INTERFACE_INCLUDE_DIRECTORIES)
-  if (NOT EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/third_party/absl)
-    file(CREATE_LINK
-         ${ABSL_INCLUDE_DIRS}/absl
-         ${CMAKE_CURRENT_SOURCE_DIR}/third_party/absl
-         SYMBOLIC)
-  endif()
   include_directories(${ABSL_INCLUDE_DIRS})
 endif()
 

MODULE.bazel

@@ -0,0 +1,37 @@
+# Copyright 2018 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.!
+
+module(
+    name = "sentencepiece",
+    version = "0.2.2",
+)
+
+# Keep in sync with the abseil-cpp GIT_TAG in CMakeLists.txt.
+bazel_dep(name = "abseil-cpp", version = "20260526.0")
+
+# Upstream darts-clone v0.32h plus the compatibility helpers (copy_array,
+# validate, ...) that the vendored third_party/darts_clone copy carries.
+bazel_dep(name = "darts-clone", version = "0.32h.bcr.1")
+
+# Upstream esaxx at the commit the vendored third_party/esaxx copy is based
+# on. The .bcr.1 revision exports esa.hxx and carries the index_type(0)
+# template-deduction fix that the int64_t instantiation of esaxx() needs.
+bazel_dep(name = "esaxx", version = "20250106.1.bcr.1")
+bazel_dep(name = "platforms", version = "1.1.0")
+
+# The .pb.cc/.pb.h files are regenerated from src/*.proto at build time, so
+# the Bazel build follows the SPM_PROTOBUF_PROVIDER=package CMake
+# configuration instead of the vendored third_party/protobuf-lite runtime.
+bazel_dep(name = "protobuf", version = "35.1")
+bazel_dep(name = "rules_cc", version = "0.2.18")

README.md

@@ -135,6 +135,7 @@ To run these benchmarks yourself, see the [reproduction instructions and scripts
 For detailed guides, API references, and advanced usage, please refer to the following resources:
 
 *   [Command Line Interface (CLI) & Build Guide](doc/cli.md)
+*   [Building with Bazel](doc/bazel.md)
 *   [C++ API Reference](doc/cpp.md)
 *   [Python API Reference](python/README.md) & [Python Module Directory](python/)
 *   [Python Tokenizer Comparison Cheat Sheet](python/tokenizer_comparison_cheat_sheet.md)

contrib/nlcodec/bpe_model_trainer_nlcodec.cc

@@ -4,8 +4,8 @@
 
 #include "contrib/nlcodec/bpe_model_trainer_nlcodec.h"
 
-#include "third_party/absl/container/flat_hash_set.h"
-#include "third_party/absl/flags/flag.h"
+#include "absl/container/flat_hash_set.h"
+#include "absl/flags/flag.h"
 #include "util.h"
 
 // Flag defined here so it's available to all binaries (spm_train, tests, etc.)

contrib/nlcodec/bpe_model_trainer_nlcodec_test.cc

@@ -8,8 +8,8 @@
 #include "sentencepiece_processor.h"
 #include "sentencepiece_trainer.h"
 #include "testharness.h"
-#include "third_party/absl/flags/flag.h"
-#include "third_party/absl/strings/str_cat.h"
+#include "absl/flags/flag.h"
+#include "absl/strings/str_cat.h"
 #include "util.h"
 
 ABSL_DECLARE_FLAG(bool, nlcodec_bpe);

data/BUILD.bazel

@@ -0,0 +1,23 @@
+# Copyright 2018 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.!
+
+package(default_visibility = ["//visibility:public"])
+
+filegroup(
+    name = "testdata",
+    srcs = glob(
+        ["**"],
+        exclude = ["BUILD.bazel"],
+    ),
+)

doc/bazel.md

@@ -0,0 +1,85 @@
+# Building SentencePiece with Bazel
+
+In addition to the [CMake build](cli.md), SentencePiece can be built with
+[Bazel](https://bazel.build). All third-party dependencies are resolved
+through the [Bazel Central Registry](https://registry.bazel.build):
+
+- [abseil-cpp](https://github.com/abseil/abseil-cpp), at the same version as
+  the `GIT_TAG` pinned in `CMakeLists.txt`;
+- [protobuf](https://github.com/protocolbuffers/protobuf): the protobuf code
+  is regenerated from `src/*.proto` at build time, matching the
+  `SPM_PROTOBUF_PROVIDER=package` CMake configuration (CMake defaults to the
+  vendored protobuf-lite runtime instead);
+- [darts-clone](https://github.com/s-yata/darts-clone), as the
+  `0.32h.bcr.1` module that carries the compatibility helpers of the
+  vendored copy;
+- [esaxx](https://github.com/hillbig/esaxx), as the `20250106.1.bcr.1`
+  module, which exports `esa.hxx` and carries the template-deduction fix
+  the vendored copy has for the `int64_t` instantiation used by
+  `--train_extremely_large_corpus`.
+
+The vendored sources under `third_party/` and the pre-generated protobuf
+code in `src/builtin_pb` are only used by CMake.
+
+## Prerequisites
+
+- Bazel 7.2.1 or later (bzlmod is used; installing via
+  [Bazelisk](https://github.com/bazelbuild/bazelisk) is recommended)
+- A C++17 compiler
+
+## Building
+
+Build the libraries and all command line tools:
+
+```bash
+bazel build //...
+```
+
+The main targets are:
+
+| Target | Description |
+| --- | --- |
+| `//src:sentencepiece` (alias `//:sentencepiece`) | Runtime library (encode/decode) |
+| `//src:sentencepiece_train` (alias `//:sentencepiece_train`) | Trainer library |
+| `//src:spm_train` | Model trainer CLI |
+| `//src:spm_encode` | Encoder CLI |
+| `//src:spm_decode` | Decoder CLI |
+| `//src:spm_normalize` | Text normalizer CLI |
+| `//src:spm_export_vocab` | Vocabulary exporter CLI |
+
+Run a tool directly:
+
+```bash
+bazel run //src:spm_train -- \
+  --input=$(pwd)/data/botchan.txt --model_prefix=$(pwd)/m --vocab_size=8000
+echo "Hello world." | bazel-bin/src/spm_encode --model=m.model
+```
+
+## Running the unit tests
+
+The unit tests are a single test binary, like the `spm_test` target that
+CMake builds with `-DSPM_BUILD_TEST=ON`:
+
+```bash
+bazel test //src:spm_test
+```
+
+## Notes
+
+- The optional CMake features `SPM_ENABLE_NFKC_COMPILE` (ICU),
+  `SPM_ENABLE_TCMALLOC`, `SPM_ENABLE_BENCHMARK`, and `SPM_NLCODEC_BPE` have no
+  Bazel equivalent yet.
+- The SentencePiece sources include third-party headers with the standard
+  paths the upstream projects export (`absl/...`, `darts.h`, `esa.hxx`), so
+  Bazel resolves them directly against the Bazel Central Registry modules.
+  CMake resolves the same includes against the abseil-cpp checkout and the
+  vendored copies under `third_party/`. No third-party code is vendored into
+  the Bazel build.
+- To use SentencePiece as a dependency in another Bazel module:
+
+  ```starlark
+  bazel_dep(name = "sentencepiece", version = "0.2.2")
+  ```
+
+  and depend on `@sentencepiece//:sentencepiece` (and
+  `@sentencepiece//:sentencepiece_train` for training support).