dawn_node: Add README.md

Includes info on how to build, known issues, remaining work.

Bug: dawn:1123
Change-Id: I0a1fe827a1aba06eea7e3574de4a7d1e0fd3f0ab
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/65161
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>

CMakeLists.txt

@@ -236,8 +236,8 @@ if (DAWN_BUILD_NODE_BINDINGS)
         if (NOT EXISTS ${DEP})
             message(FATAL_ERROR
                 "DAWN_BUILD_NODE_BINDINGS requires missing dependency '${DEP}'\n"
-                "Try running:\n"
+                "Please follow the 'Fetch dependencies' instructions at:\n"
-                "gclient sync --gclientfile=scripts/standalone-with-node.gclient"
+                "./src/dawn_node/README.md"
             )
         endif()
     endforeach()

src/dawn_node/README.md

@@ -0,0 +1,71 @@
+# Dawn bindings for NodeJS
+
+Note: This code is currently WIP. There are a number of [known issues](#known-issues).
+
+## Building
+
+## System requirements
+
+- [CMake 3.10](https://cmake.org/download/) or greater
+- [Go 1.13](https://golang.org/dl/) or greater
+
+## Install `depot_tools`
+
+Dawn uses the Chromium build system and dependency management so you need to [install depot_tools] and add it to the PATH.
+
+[install depot_tools]: http://commondatastorage.googleapis.com/chrome-infra-docs/flat/depot_tools/docs/html/depot_tools_tutorial.html#_setting_up
+
+### Fetch dependencies
+
+First, the steps are similar to [`doc/building.md`](../../docs/building.md), but instead of the `Get the code` step, run:
+
+```sh
+# Clone the repo as "dawn"
+git clone https://dawn.googlesource.com/dawn dawn && cd dawn
+
+# Bootstrap the NodeJS binding gclient configuration
+cp scripts/standalone-with-node.gclient .gclient
+
+# Fetch external dependencies and toolchains with gclient
+gclient sync
+```
+
+### Build
+
+Currently, the node bindings can only be built with CMake:
+
+```sh
+mkdir <build-output-path>
+cd <build-output-path>
+cmake <dawn-root-path> -GNinja -DDAWN_BUILD_NODE_BINDINGS=1 -DDAWN_ENABLE_PIC=1
+ninja dawn.node
+```
+
+### Running WebGPU CTS
+
+1. [Build](#build) the `dawn.node` NodeJS module.
+2. Checkout the [WebGPU CTS repo](https://github.com/gpuweb/cts)
+
+```sh
+./src/dawn_node/tools/run-cts --cts=<path-to-webgpu-cts> --dawn-node=<path-to-dawn.node> [WebGPU CTS query]
+```
+
+If this fails with the error message `TypeError: expander is not a function or its return value is not iterable`, try appending `--build=false` to the start of the `run-cts` command line flags.
+
+To test against SwiftShader instead of the default Vulkan device, prefix `./src/dawn_node/tools/run-cts` with `VK_ICD_FILENAMES=<swiftshader-cmake-build>/Linux/vk_swiftshader_icd.json`
+
+## Known issues
+
+- Many WebGPU CTS tests are currently known to fail
+- Dawn uses special token values for some parameters / fields. These are currently passed straight through to dawn from the JavaScript. discussions: [1](https://dawn-review.googlesource.com/c/dawn/+/64907/5/src/dawn_node/binding/Converter.cpp#167), [2](https://dawn-review.googlesource.com/c/dawn/+/64907/5/src/dawn_node/binding/Converter.cpp#928), [3](https://dawn-review.googlesource.com/c/dawn/+/64909/4/src/dawn_node/binding/GPUTexture.cpp#42)
+- Backend validation is currently always set to 'full' to aid in debugging. This can be extremely slow. [discussion](https://dawn-review.googlesource.com/c/dawn/+/64916/4/src/dawn_node/binding/GPU.cpp#25)
+- Attempting to call `new T` in JavaScript, where `T` is an IDL interface type, should result in a TypeError "Illegal constructor". [discussion](https://dawn-review.googlesource.com/c/dawn/+/64902/9/src/dawn_node/interop/WebGPU.cpp.tmpl#293)
+- `GPUDevice` currently maintains a list of "lost promises". This should return the same promise. [discussion](https://dawn-review.googlesource.com/c/dawn/+/64906/6/src/dawn_node/binding/GPUDevice.h#107)
+
+## Remaining work
+
+- Have the IDL interop generator produce default values for parameters (instead of std::optional). [discussion](https://dawn-review.googlesource.com/c/dawn/+/64912/5/src/dawn_node/binding/GPURenderBundleEncoder.cpp#166)
+- Investigate CTS failures that are not expected to fail.
+- Generated includes live in `src/` for `dawn_node`, but outside for Dawn. [discussion](https://dawn-review.googlesource.com/c/dawn/+/64903/9/src/dawn_node/interop/CMakeLists.txt#56)
+- Hook up to presubmit bots (CQ / Kokoro)
+- `binding::GPU` will require significant rework [once Dawn implements the device / adapter creation path properly](https://dawn-review.googlesource.com/c/dawn/+/64916/4/src/dawn_node/binding/GPU.cpp).