docs(guides): add guide for explaining how to compile custom chips to WASM (#254)

Author: krisjdev

docs/guides/custom-chips-as-wasm-vscode-dev-container.png

@@ -0,0 +1,131 @@
+---
+title: Compiling custom chips to WASM
+sidebar_label: Custom chips as WASM
+description: Compile your custom chips to WASM for use with VS Code or the Wokwi CLI
+keywords: [Visual Studio Code, VS Code, custom chip, compiling, WASM, web assembly, API, chips, chip, docker]
+---
+
+import VsCodeDevContainerImage from './custom-chips-as-wasm-vscode-dev-container.png';
+import VsCodeRemoteContainerImage from './custom-chips-as-wasm-vscode-remote-container-button.png';
+
+Custom components written with the [Chips API](/chips-api/getting-started) can be compiled into WebAssembly (WASM) for
+use with the Wokwi VS Code extension or the Wokwi CLI.
+
+The WASM binary can be compiled by GitHub Actions, a container, or locally. This guide will cover all three
+approaches.
+
+The simplest way to get started is by cloning/forking the [inverter-chip](https://github.com/wokwi/inverter-chip)
+example repository from the Wokwi GitHub. You can then compile locally, use the dev container feature from VS
+Code, or push to GitHub to compile the WASM binary. This repository will also be referenced multiple times throughout
+this guide, so it is worth having a look at.
+
+## Configure your project
+Before compiling your chip, you should make sure your project is configured properly to ensure that they can work in
+Wokwi.
+
+### Wokwi configuration
+A custom chip requires a `[[chip]]` key in `wokwi.toml`. This key specifies the name and binary used by the custom chip.
+Wokwi also requires a JSON file that describes the pinout of the chip. This JSON file should have the same name as the
+WASM binary, but with its extension changed to `.json` instead of `.wasm`, e.g. `inverter.chip.wasm` is paired with
+`inverter.chip.json`. To configure the chip JSON file properly, see the docs on [custom chip definitions](../chips-api/chip-json).
+
+An example excerpt from `wokwi.toml`:
+```toml
+[[chip]]
+name = 'inverter' # To use the chip in diagram.json, add a part with "chip-inverter" type.
+binary = 'chips/inverter.chip.wasm'
+```
+
+Multiple chips can be added to the same project by adding multiple `[[chip]]` keys, each with different `name` and
+`binary` values.
+
+### Source files
+:::note
+If you are cloning/forking the inverter chip repository, then you can skip this section.
+:::
+
+If you are setting up your project from scratch, you need to ensure that the Wokwi C API is present within your source
+files. It is available from [wokwi.com/api/chips/wokwi-api.h](https://wokwi.com/api/chips/wokwi-api.h).
+
+You need to ensure that it is included in your project, otherwise you will not be able to make use of the Chips API.
+
+## Compilation methods
+
+### GitHub Actions
+
+If you have cloned the inverter chip repository, then it has been configured and is ready for you to modify it to your
+needs. It will automatically compile the binary once a push is made to the repository, and will also automatically
+generate a GitHub release if you push a tag that starts with a "v", e.g. `v1.0.3`.
+
+If you did not clone the inverter chip repository and are wanting to configure your own actions, then consider looking
+at the [build workflow file](https://github.com/wokwi/inverter-chip/blob/ff72418a11d9d56621731ab3d373c952b1b508ea/.github/workflows/build.yaml).
+If you do not want to use this action, then see the steps for compiling locally.
+
+
+### VS Code dev container
+The inverter chip repository comes with a dev container configuration file that will automatically handle setting up a
+Docker container for you to build your binaries in. To make use of this, simply open the custom chip folder in a
+container by pressing <kbd>F1</kbd> and searching for "Dev Containers: Open Folder in Container...". 
+
+<figure>
+  <img src={VsCodeDevContainerImage} alt="Opening a dev container in VS Code via the command palette" />
+  <figcaption>Opening a dev container in VS Code via the command palette</figcaption>
+</figure>
+
+Alternatively, you can click the icon bottom left of the VS Code window, and click on "Reopen in Container".
+
+<figure>
+    <img src={VsCodeRemoteContainerImage}  style={{margin: "auto"}} alt="Opening a dev container in VS Code via a dedicated button"/>
+  <figcaption>Opening a dev container in VS Code via a dedicated button</figcaption>
+</figure>
+
+Once done, you should be presented with a terminal window where you can now run `make`. This will run the `Makefile` in
+the repository, and your generated WASM files should appear in `dist/`.
+
+### Docker
+You can use the prebuilt [wokwi/builder-clang-wasm](https://hub.docker.com/r/wokwi/builder-clang-wasm) image to compile
+your project in a Docker environment.
+
+To get started, simply navigate to the root of your project and run:
+```bash
+docker run --rm -u 1000:1000 -v ${PWD}:/src wokwi/builder-clang-wasm:latest make
+```
+
+After fetching the image, this will command automatically execute the `Makefile` in the project. In the case of the
+inverter example, it will create the `dist/` directory, compile the binary into `dist/chip.wasm` and copy `chip.json` to 
+`dist/`.
+
+You can enter an interactive session with the following:
+```bash
+docker run --rm -it -u 1000:1000 -v ${PWD}:/src wokwi/builder-clang-wasm:latest
+```
+
+:::info
+The argument `-u 1000:1000` is required since otherwise you may run into issues with permissions (such as the container
+being unable to open files or create directories). If your computer has multiple users, you may have to update
+the value to something other than `1000` - check the output of the `id` command on the host to get the proper value.
+:::
+
+
+### Building locally
+
+You will need to configure your environment to be able to build WASM assemblies locally. This part of the documentation
+is written with Ubuntu/Debian distros in mind, so you may have to adjust these instructions to your machine.
+
+1. Install `wasi-libc` with `sudo apt install wasi-libc`
+2. Install the missing `libclang_rt.builtins-wasm32.a` library
+    1. Download `libclang_rt-27.0.tar.gz` from the [wasi-sdk GitHub releases](https://github.com/WebAssembly/wasi-sdk/releases)
+    2. Extract `libclang_rt-27.0/wasm32-unknown-wasi/libclang_rt.builtins.a` to `/usr/lib/llvm-???/lib/clang/???/lib/wasi/`
+    :::info
+    Replace the `???` in the path above with the currently installed LLVM version number on your system. Check by
+    running `clang -v` and looking at the major release number.
+    :::
+    3. Rename the copied file from `libclang_rt.builtins.a` to `libclang_rt.builtins-wasm32.a`
+
+You can now compile WASM binaries! To test, clone the inverter repository and run 
+`clang --target=wasm32-unknown-wasi -nostartfiles -Wl,--import-memory -Wl,--export-table -Wl,--no-entry -Werror -o dist/chip.wasm src/main.c`.
+
+You may have to update the `Makefile` to remove the `--sysroot` argument, as `wasi-libc` will be installed to a different
+directory than what `--sysroot` is set to.
+
+If successful, you should now have `chip.wasm` under `dist/`!

docs/guides/custom-chips-as-wasm-vscode-remote-container-button.png

@@ -13,6 +13,7 @@ module.exports = {
       'guides/circuitpython',
       'guides/esp32',
       'guides/esp32-wifi',
+      'guides/custom-chips-to-wasm'
     ],
     'Diagram Reference': [
       'diagram-format',