rescript-lang · cknitt · Jan 17, 2026 · Jan 17, 2026 · Jan 17, 2026 · Jan 17, 2026
diff --git a/.devcontainer/.dockerignore b/.devcontainer/.dockerignore
@@ -46,9 +46,6 @@ node_modules
 *.dump
 coverage
 
-.ninja_log
-.bsdeps
-.bsbuild
 lib/ocaml
 tests/build_tests/*/lib/
 #ignore temporary directory
@@ -94,6 +91,3 @@ tests/analysis_tests/**/*.bs.js
 # package tarballs
 package.tgz
 *.exe
-
-/ninja/ninja
-/ninja/build.ninja
diff --git a/.devcontainer/Dockerfile b/.devcontainer/Dockerfile
@@ -5,9 +5,7 @@ LABEL org.opencontainers.image.description="Docker image for ReScript developmen
 RUN sudo apt-get update && export DEBIAN_FRONTEND=noninteractive \
     && apt-get -y install --no-install-recommends \
     cmake \
-    ninja-build \
     musl-tools \
-    python-is-python3 \
     && rm -rf /var/lib/apt/lists/*
 
 # Install OPAM

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -296,43 +296,6 @@ jobs:
       - name: Copy compiler exes to platform bin dir
         run: node scripts/copyExes.js --compiler
 
-      - name: Restore ninja build cache
-        id: ninja-build-cache
-        uses: actions/cache@v5
-        with:
-          path: ninja/ninja${{ matrix.exe-suffix }}
-          key: ninja-build-v2-${{ matrix.os }}-${{ hashFiles('ninja/src/**') }}
-
-      - name: Setup Python for ninja build
-        if: steps.ninja-build-cache.outputs.cache-hit != 'true'
-        uses: actions/setup-python@v6
-        with:
-          python-version: "3.13"
-
-      - name: Setup MSVC for ninja build (Windows)
-        if: steps.ninja-build-cache.outputs.cache-hit != 'true' && runner.os == 'Windows'
-        uses: TheMrMilchmann/setup-msvc-dev@v4
-        with:
-          arch: x64
-
-      - name: Build ninja
-        if: steps.ninja-build-cache.outputs.cache-hit != 'true' && runner.os != 'Linux'
-        run: node scripts/buildNinjaBinary.js
-
-      - name: Build ninja (Linux static)
-        if: steps.ninja-build-cache.outputs.cache-hit != 'true' && runner.os == 'Linux'
-        env:
-          LDFLAGS: -static
-        run: node scripts/buildNinjaBinary.js
-
-      # Prevent ninja being rebuilt on playground build step later
-      - name: Touch ninja/ninja
-        if: ${{ matrix.build_playground && steps.ninja-build-cache.outputs.cache-hit == 'true' }}
-        run: touch ninja/ninja${{ matrix.exe-suffix }}
-
-      - name: Copy ninja exe to platform bin dir
-        run: node scripts/copyExes.js --ninja
-
       - name: "Syntax: Run tests"
         env:
           ROUNDTRIP_TEST: ${{ runner.os == 'Windows' && '0' || '1' }}

diff --git a/.gitignore b/.gitignore
@@ -48,9 +48,6 @@ node_modules
 *.dump
 coverage
 
-.ninja_log
-.bsdeps
-.bsbuild
 lib/ocaml
 tests/build_tests/*/lib/
 #ignore temporary directory

diff --git a/AGENTS.md b/AGENTS.md
@@ -25,9 +25,8 @@ The Makefile’s targets build on each other in this order:
 
 1. `yarn-install` runs automatically for targets that need JavaScript tooling (lib, playground, tests, formatting, etc.).
 2. `build` (default target) builds the toolchain binaries (all copied into `packages/@rescript/<platform>/bin`):
-   - `compiler` builds the dune executables (`bsc`, `bsb_helper`, `rescript-*`, `ounit_tests`, etc.).
+   - `compiler` builds the dune executables (`bsc`, `rescript-*`, `ounit_tests`, etc.).
    - `rewatch` builds the Rust-based ReScript build system and CLI.
-   - `ninja` bootstraps the ninja binary (part of the legacy build system).
 3. `lib` uses those toolchain outputs to build the runtime sources.
 4. Test targets (`make test`, `make test-syntax`, etc.) reuse everything above.
 
@@ -82,7 +81,6 @@ compiler/
 ├── ml/              # OCaml compiler infrastructure
 ├── core/            # Core compilation (lam_*, js_* files)
 ├── ext/             # Extended utilities and data structures
-├── bsb/             # Legacy build system
 └── gentype/         # TypeScript generation
 
 analysis/            # Language server and tooling
@@ -254,7 +252,6 @@ The compiler is designed for fast feedback loops and scales to large codebases:
 - **Build System**: dune with profiles (dev, release, browser)
 - **JavaScript**: Node.js 20+ for tooling
 - **Rust**: Toolchain needed for rewatch
-- **Python**: 3 required for building ninja
 
 ## Common Tasks
 
@@ -283,7 +280,7 @@ The compiler is designed for fast feedback loops and scales to large codebases:
 
 ### Rewatch Architecture
 
-Rewatch is the modern build system written in Rust that replaces the legacy bsb (BuckleScript) build system. It provides faster incremental builds, better error messages, and improved developer experience.
+Rewatch is ReScript's build system written in Rust. It provides fast incremental builds, better error messages, and improved developer experience.
 
 #### Key Components
 
@@ -410,13 +407,6 @@ When clippy suggests refactoring that could impact performance, consider the tra
 
 - **Avoid Unnecessary Type Conversions**: When threading parameters through multiple function calls, use consistent types (e.g., `String` throughout) rather than converting between `String` and `&str` at each boundary. This eliminates unnecessary allocations and conversions.
 
-#### Compatibility with Legacy bsb
-
-- **Command-line Flags**: Maintain compatibility with bsb flags where possible
-- **Configuration**: Support both old (`bs-*`) and new field names
-- **Output Format**: Generate compatible build artifacts
-- **Error Messages**: Provide clear migration guidance
-
 ### Common Tasks
 
 #### Adding New CLI Flags

diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -14,6 +14,7 @@
 
 #### :boom: Breaking Change
 
+- Remove the legacy build system. Going forward, only the modern build system is supported, and the `rescript-legacy` command is not available anymore. https://github.com/rescript-lang/rescript/pull/8186
 - `Int.fromString` and `Float.fromString` use stricter number parsing and no longer uses an explicit radix argument, but instead supports parsing hexadecimal, binary and exponential notation.
 - Remove `external-stdlib` configuration option from `rescript.json`. This option was rarely used and is no longer supported.
 

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
@@ -17,7 +17,6 @@ Happy hacking!
 - [Node.js](https://nodejs.org/) v22.x or newer
 - [Yarn CLI](https://yarnpkg.com/getting-started/install) (can be installed with `corepack`, Homebrew, etc)
 - C compiler toolchain (usually installed with `xcode` on Mac)
-- Python <= 3.11 (required to build ninja)
 - Rust toolchain (required to build rewatch; follow the instructions at https://www.rust-lang.org/tools/install and install the version listed as `rust-version` in `rewatch/Cargo.toml`)
 - `opam` (OCaml Package Manager) v2.2.0 or newer
 - VSCode (+ [OCaml Platform Extension](https://marketplace.visualstudio.com/items?itemName=ocamllabs.ocaml-platform))
@@ -103,12 +102,10 @@ You can also open this dev container with [GitHub Codespaces](https://github.com
 
 ## Building the Compiler
 
-To build the compiler, the build tools (rewatch and ninja), and the ReScript runtime/standard library, just run:
-
 Main targets:
 
 ```sh
-# Build the compiler and the build tools (rewatch and ninja)
+# Build the compiler and the build system (rewatch)
 make
 
 # Build the runtime/standard library
@@ -127,9 +124,6 @@ make compiler
 # Build rewatch only
 make rewatch
 
-# Build the ninja tool only
-make ninja
-
 # Run syntax tests
 make test-syntax
 
@@ -230,10 +224,10 @@ node scripts/test.js -mocha
 
 **Run build system test (integration tests):**
 
-This will run the whole build system test suite defined in `tests/build_tests`.
+This will run the build system test suite defined in `tests/build_tests`.
 
 ```
-node scripts/test.js -bsb
+node scripts/test.js -build
 ```
 
 **Run ounit tests:**

diff --git a/CREDITS.md b/CREDITS.md
@@ -44,10 +44,6 @@ This file was imported but changed significantly in iterations later.
 
 ReScript compiler unit test builds on [OUnit](http://ounit.forge.ocamlcore.org/)
 
-## Ninja
-
-Thanks to [ninja-build](https://ninja-build.org), ReScript also comes with a blazing fast build tool on top of it, `ninja` is a truly [well engineered](http://aosabook.org/en/posa/ninja.html) scalable build tool.
-
 ## Bloomberg and Facebook
 
 Thanks to [Bloomberg](https://www.techatbloomberg.com) and [Facebook](https://github.com/facebook/). This project began at Bloomberg and was published in 2016; without the support of Bloomberg, it would not have happened. This project's funded by Facebook since July 2017.
diff --git a/Makefile b/Makefile
@@ -59,7 +59,7 @@ RUNTIME_BUILD_STAMP := packages/@rescript/runtime/.buildstamp
 
 # Default target
 
-build: compiler rewatch ninja
+build: compiler rewatch
 
 # Yarn
 
@@ -72,25 +72,6 @@ $(YARN_INSTALL_STAMP): $(YARN_INSTALL_SOURCES)
 	yarn install
 	touch $@
 
-# Ninja
-
-NINJA_SOURCES = $(wildcard ninja/src/*.cc ninja/src/*.h) $(wildcard ninja/*.py)
-NINJA_EXE = $(BIN_DIR)/ninja.exe
-
-ninja: $(NINJA_EXE)
-
-ninja/ninja: $(NINJA_SOURCES)
-ifeq ($(OS),Darwin)
-	export CXXFLAGS="-flto"
-endif
-	cd ninja && python3 configure.py --bootstrap --verbose
-
-$(NINJA_EXE): ninja/ninja
-	$(call COPY_EXE,$<,$@)
-
-clean-ninja:
-	rm -rf $(NINJA_EXE) ninja/build.ninja ninja/build ninja/misc/__pycache__ ninja/ninja
-
 # Rewatch
 
 REWATCH_SOURCES = $(shell find rewatch/src -name '*.rs') rewatch/Cargo.toml rewatch/Cargo.lock rewatch/rust-toolchain.toml
@@ -119,7 +100,7 @@ clean-rewatch:
 
 COMPILER_SOURCE_DIRS := compiler tests analysis tools
 COMPILER_SOURCES = $(shell find $(COMPILER_SOURCE_DIRS) -type f \( -name '*.ml' -o -name '*.mli' -o -name '*.dune' -o -name dune -o -name dune-project \))
-COMPILER_BIN_NAMES := bsc bsb_helper rescript-legacy rescript-editor-analysis rescript-tools
+COMPILER_BIN_NAMES := bsc rescript-editor-analysis rescript-tools
 COMPILER_EXES := $(addsuffix .exe,$(addprefix $(BIN_DIR)/,$(COMPILER_BIN_NAMES)))
 COMPILER_DUNE_BINS := $(addsuffix $(PLATFORM_EXE_EXT),$(addprefix $(DUNE_BIN_DIR)/,$(COMPILER_BIN_NAMES)))
 
@@ -166,20 +147,20 @@ artifacts: lib
 bench: compiler
 	$(DUNE_BIN_DIR)/syntax_benchmarks
 
-test: lib ninja
+test: lib
 	node scripts/test.js -all
 
-test-analysis: lib ninja
+test-analysis: lib
 	make -C tests/analysis_tests clean test
 
-test-reanalyze: lib ninja
+test-reanalyze: lib
 	make -C tests/analysis_tests/tests-reanalyze/deadcode test
 
 # Benchmark reanalyze on larger codebase (COPIES=N for more files)
-benchmark-reanalyze: lib ninja
+benchmark-reanalyze: lib
 	make -C tests/analysis_tests/tests-reanalyze/deadcode-benchmark benchmark COPIES=$(or $(COPIES),50)
 
-test-tools: lib ninja
+test-tools: lib
 	make -C tests/tools_tests clean test
 
 test-syntax: compiler
@@ -188,7 +169,7 @@ test-syntax: compiler
 test-syntax-roundtrip: compiler
 	ROUNDTRIP_TEST=1 ./scripts/test_syntax.sh
 
-test-gentype: lib ninja
+test-gentype: lib
 	make -C tests/gentype_tests/typescript-react-example clean test
 	make -C tests/gentype_tests/stdlib-no-shims clean test
 
@@ -217,7 +198,7 @@ $(PLAYGROUND_BUILD_STAMP): $(COMPILER_SOURCES)
 # Creates all the relevant core and third party cmij files to side-load together with the playground bundle
 playground-cmijs: $(PLAYGROUND_CMI_BUILD_STAMP)
 
-$(PLAYGROUND_CMI_BUILD_STAMP): $(RUNTIME_BUILD_STAMP) $(NINJA_EXE)
+$(PLAYGROUND_CMI_BUILD_STAMP): $(RUNTIME_BUILD_STAMP)
 	yarn workspace playground build
 
 playground-test: playground
@@ -244,11 +225,11 @@ clean-gentype:
 
 clean-tests: clean-gentype
 
-clean: clean-lib clean-compiler clean-rewatch clean-ninja
+clean: clean-lib clean-compiler clean-rewatch
 
 dev-container:
 	docker build -t rescript-dev-container docker
 
 .DEFAULT_GOAL := build
 
-.PHONY: yarn-install build ninja rewatch compiler lib artifacts bench test test-analysis test-reanalyze benchmark-reanalyze test-tools test-syntax test-syntax-roundtrip test-gentype test-rewatch test-all playground playground-compiler playground-test playground-cmijs playground-release format checkformat clean-ninja clean-rewatch clean-compiler clean-lib clean-gentype clean-tests clean dev-container
+.PHONY: yarn-install build rewatch compiler lib artifacts bench test test-analysis test-reanalyze benchmark-reanalyze test-tools test-syntax test-syntax-roundtrip test-gentype test-rewatch test-all playground playground-compiler playground-test playground-cmijs playground-release format checkformat clean-rewatch clean-compiler clean-lib clean-gentype clean-tests clean dev-container
diff --git a/README.md b/README.md
@@ -96,9 +96,6 @@ ReScript is licensed under LGPL version 3, with relaxed rules about creating and
 
 The ReScript parser (subdirectory `compiler/syntax`) is licensed under the [MIT License](compiler/syntax/LICENSE).
 
-The `ninja` subdirectory contains the vendored [ninja](https://github.com/ninja-build/ninja) build system.
-Refer to its copyright and license notices for information about its licensing.
-
 ## 🏅 Acknowledgments
 
 ReScript was originally created by [Hongbo Zhang](https://github.com/bobzhang) in 2015.

diff --git a/analysis/examples/example-project/src/Json.res b/analysis/examples/example-project/src/Json.res
@@ -1,6 +1,4 @@
 @@ocaml.doc(" # Json parser
- *
- * Works with bucklescript and bsb-native
  *
  * ## Basics
  *

diff --git a/analysis/examples/larger-project/.merlin b/analysis/examples/larger-project/.merlin
diff --git a/analysis/examples/workspace-project/.gitignore b/analysis/examples/workspace-project/.gitignore
@@ -23,7 +23,6 @@ lib
 *.mliast
 .vscode
 .merlin
-.bsb.lock
 /node_modules/
 package-lock.json
 yarn.lock
diff --git a/analysis/vendor/json/Json.ml b/analysis/vendor/json/Json.ml
@@ -1,6 +1,4 @@
 (** # Json parser
- *
- * Works with bucklescript and bsb-native
  *
  * ## Basics
  *

diff --git a/biome.json b/biome.json
@@ -66,7 +66,6 @@
       "lib/es6/**",
       "lib/js/**",
       "lib/bs/**",
-      "ninja/**",
       "playground/**",
       "*.bs.js",
       "*.res.js",