initial port to wasm

.bazelrc

@@ -45,3 +45,12 @@ build:tsan --linkopt=-fsanitize=thread
 build:tsan --strip=never
 build:tsan --features=dbg
 build:tsan --compilation_mode=dbg
+
+# WebAssembly (WASM) configuration
+# Usage: bazel build --config=wasm //...
+# Compiles using the hermetic emsdk toolchain downloaded automatically by Bazel.
+build:wasm --platforms=@emsdk//:platform_wasm
+build:wasm --cpu=wasm
+build:wasm --cxxopt=-std=c++20
+build:wasm --host_cxxopt=-std=c++20
+build:wasm --compilation_mode=opt

BUILD.bazel

@@ -72,6 +72,13 @@ config_setting(
     define_values = {"asan": "true"},
 )
 
+# WebAssembly (WASM) build configuration
+# Usage: bazel build --config=wasm //...
+config_setting(
+    name = "build_wasm",
+    values = {"cpu": "wasm"},
+)
+
 
 load("@rules_cc//cc:defs.bzl", "cc_library")
 

CPPVARIABLES.bzl

@@ -7,7 +7,6 @@ DDS_CPPOPTS = select({
         "-fPIC",
         "-Wpedantic",
         "-Wall",
-        "-Wno-character-conversion",
         "-Werror",
     ],
     "//:debug_build_macos": [
@@ -16,7 +15,6 @@ DDS_CPPOPTS = select({
         "-fPIC",
         "-Wpedantic",
         "-Wall",
-        "-Wno-character-conversion",
         "-Werror",
     ],
     "//:build_linux": [
@@ -51,6 +49,14 @@ DDS_CPPOPTS = select({
         "/WX",
         "/permissive-",
     ],
+    "//:build_wasm": [
+        "-O3",
+        "-flto",
+        "-Wpedantic",
+        "-Wall",
+        "-Werror",
+        "-fexceptions",
+    ],
     "//conditions:default": [
         "-std=c++20"
     ],
@@ -64,6 +70,7 @@ DDS_LOCAL_DEFINES = select({
     "//:debug_build_macos": [],
     "//:build_linux": [],
     "//:debug_build_linux": [],
+    "//:build_wasm": ["__WASM__"],
     "//conditions:default": [],
 }) + select({
     "//:debug_all": ["DDS_DEBUG_ALL"],

MODULE.bazel

@@ -9,6 +9,7 @@ bazel_dep(name = "googletest", version = "1.17.0.bcr.2")
 bazel_dep(name = "pybind11_bazel", version = "3.0.1")
 bazel_dep(name = "rules_python", version = "2.0.1")
 bazel_dep(name = "toolchains_llvm", version = "1.7.0")
+bazel_dep(name = "emsdk", version = "5.0.7")
 
 llvm = use_extension("@toolchains_llvm//toolchain/extensions:llvm.bzl", "llvm")
 llvm.toolchain(
@@ -29,4 +30,5 @@ python.toolchain(
 )
 use_repo(python, "python_3_14")
 
-register_toolchains("@llvm_toolchain//:all")
+register_toolchains("@llvm_toolchain//:all")
+register_toolchains("@emsdk//:all")

docs/wasm_build.md

@@ -0,0 +1,136 @@
+# WebAssembly (WASM) Build Guide
+
+This document explains how to build the DDS library and examples for WebAssembly using Bazel.
+
+## Prerequisites
+
+### Bazel
+
+Bazel 7.x or later is required. Install using your package manager or download from:
+https://bazel.build/install
+
+The Emscripten SDK (emsdk) does NOT need to be manually installed. Bazel will automatically download, configure, and cache the appropriate hermetic Emscripten toolchain for your host platform as part of the build process.
+
+## Building WASM Examples
+
+### Build All Examples
+
+```bash
+cd /workspaces/dds
+bazel build //examples:all_examples_wasm
+```
+
+### Build Specific Example
+
+```bash
+bazel build //examples:solve_board_wasm
+```
+
+### Output Files
+
+the output files will be located in:
+```
+bazel-bin/examples/
+```
+
+Depending on the target, you'll get:
+- `target.js` - JavaScript bindings
+- `target.wasm` - WebAssembly binary
+
+
+## Available WASM Targets
+
+The following example targets are available for WASM builds:
+
+### Implemented Examples
+- `solve_board` - Solves a single board (produces .js and .wasm)
+
+- `analyse_play_bin` - Analyze play from binary format
+
+
+## WASM Build Configuration
+
+The WASM build is configured through:
+
+1. **BUILD.bazel** - Defines the WASM config_setting:
+   ```python
+   config_setting(
+       name = "build_wasm",
+       values = {"cpu": "wasm"},
+   )
+   ```
+
+2. **CPPVARIABLES.bzl** - Specifies WASM-specific compiler flags:
+   - Optimization: `-O3 -flto`
+   - Exceptions: `-fexceptions`
+   - Define: `-D__WASM__`
+
+3. **.bazelrc** - Contains the `wasm` profile:
+   ```
+   build:wasm --platforms=@emsdk//:platform_wasm
+   build:wasm --cpu=wasm
+   build:wasm --cxxopt=-std=c++20
+   build:wasm --host_cxxopt=-std=c++20
+   build:wasm --compilation_mode=opt
+   ```
+
+## Running WASM Examples
+
+After building, you can run the examples:
+
+### Node.js (requires Node.js installed)
+
+```bash
+node bazel-bin/examples/solve_board.js
+```
+
+### Web Browser (TODO)
+
+For HTML targets, open the generated HTML file in a web browser:
+```bash
+# Copy the output files to a web-accessible location
+cp bazel-bin/examples/solve_board.* /path/to/webserver/
+
+# Then open in browser at http://localhost:8000/solve_board.html
+```
+
+## Compilation Flags
+
+The WASM build uses the following key flags:
+
+| Flag | Purpose |
+|------|---------|
+| `-O3` | Aggressive optimization |
+| `-flto` | Link-time optimization |
+| `-fexceptions` | Enable C++ exceptions |
+| `-D__WASM__` | Defines `__WASM__` preprocessor constant |
+| `-sWASM=1` | Emscripten WASM output (link flag) |
+| `-sALLOW_MEMORY_GROWTH=1` | Allow heap growth at runtime |
+| `-sINITIAL_MEMORY=268435456` | Configure 256MB initial memory |
+
+## C++ Standard
+
+The WASM build uses C++20 as specified in `.bazelrc`:
+```
+build:wasm --cxxopt=-std=c++20
+```
+
+## Related Documentation
+
+- [Emscripten Documentation](https://emscripten.org/docs/)
+- [Bazel Build System](https://bazel.build/docs)
+- [DDS C++ API](c++_interface.md)
+- [Build System Overview](BUILD_SYSTEM.md)
+
+## Next Steps
+
+To integrate WASM builds into CI/CD:
+1. See `.github/workflows/ci_linux.yml` and `.github/workflows/ci_macos.yml`
+2. Store WASM artifacts for download/release
+
+## Development Notes
+
+- The `__WASM__` preprocessor constant is added initially to bypass error, need to check again whether we can remove
+- Some threading and platform-specific features are disabled for WASM
+- The build flow for a reusable library wasm 
+- A good HTML example