feat(docs): Documenting noir codegen

docs/docs/getting_started/tooling/noir_codegen.md

@@ -0,0 +1,113 @@
+---
+title: Noir Codegen for TypeScript
+description: Learn how to use Noir codegen to generate TypeScript bindings 
+keywords: [Nargo, Noir, compile, TypeScript]
+sidebar_position: 2
+---
+
+When using TypeScript, it is extra work to interpret Noir program outputs in a type-safe way. Third party libraries may exist for popular Noir programs, but they are either hard to find or unmaintained.
+
+Now you can generate TypeScript bindings for your Noir programs in two steps: 
+1. Exporting Noir functions using `nargo export`
+2. Using the TypeScript module `noir_codegen` to generate TypeScript binding
+
+**Note:** you can only export functions from a Noir *library* (not binary or contract program types).
+
+## Installation
+
+### Your TypeScript project
+
+If you don't already have a TypeScript project you can add the module with `yarn` (or `npm`), then initialize it:
+
+```bash
+yarn add typescript -D
+npx tsc --init
+```
+
+### Add TypeScript module - `noir_codegen`
+
+The following command will add the module to your project's devDependencies:
+
+```bash
+yarn add @noir-lang/noir_codegen -D
+```
+
+### Nargo library
+Make sure you have Nargo, v0.25.0 or greater, installed. If you don't, follow the [installation guide](../installation/index.md). 
+
+If you're in a new project, make a `circuits` folder and create a new Noir library:
+
+```bash
+mkdir circuits && cd circuits
+nargo new --lib myNoirLib
+```
+
+## Usage
+
+### Export ABI of specified functions
+
+First go to the `.nr` files in your Noir library, and add the `#[export]` macro to each function that you want to use in TypeScript.
+
+```rust
+#[export]
+fn your_function(...
+```
+
+From your Noir library (where `Nargo.toml` is), run the following command:
+
+```bash
+nargo export
+```
+
+You will now have an `export` directory with a .json file per exported function.
+
+You can also specify the directory of Noir programs using `--program-dir`, for example:
+
+```bash
+nargo export --program-dir=./circuits/myNoirLib
+```
+
+### Generate TypeScript bindings from exported functions
+
+To use the `noir-codegen` package we added to the TypeScript project:
+
+```bash
+yarn noir-codegen ./export/your_function.json
+```
+
+This creates an `exports` directory with an `index.ts` file containing all exported functions.
+
+**Note:** adding `--out-dir` allows you to specify an output dir for your TypeScript bindings to go. Eg:
+
+```bash
+yarn noir-codegen ./export/*.json --out-dir ./path/to/output/dir
+```
+
+## Example .nr function to .ts output
+
+Consider a Noir library with this function:
+
+```rust
+#[export]
+fn not_equal(x: Field, y: Field) -> bool {
+    x != y
+}
+```
+
+After the export and codegen steps, you should have an `index.ts` like:
+
+```typescript
+export type Field = string;
+
+
+export const is_equal_circuit: CompiledCircuit = {"abi":{"parameters":[{"name":"x","type":{"kind":"field"},"visibility":"private"},{"name":"y","type":{"kind":"field"},"visibility":"private"}],"param_witnesses":{"x":[{"start":0,"end":1}],"y":[{"start":1,"end":2}]},"return_type":{"abi_type":{"kind":"boolean"},"visibility":"private"},"return_witnesses":[4]},"bytecode":"H4sIAAAAAAAA/7WUMQ7DIAxFQ0Krrr2JjSGYLVcpKrn/CaqqDQN12WK+hPBgmWd/wEyHbF1SS923uhOs3pfoChI+wKXMAXzIKyNj4PB0TFTYc0w5RUjoqeAeEu1wqK0F54RGkWvW44LPzExnlkbMEs4JNZmN8PxS42uHv82T8a3Jeyn2Ks+VLPcO558HmyLMCDOXAXXtpPt4R/Rt9T36ss6dS9HGPx/eG17nGegKBQAA"};
+
+export async function is_equal(x: Field, y: Field, foreignCallHandler?: ForeignCallHandler): Promise<boolean> {
+  const program = new Noir(is_equal_circuit);
+  const args: InputMap = { x, y };
+  const { returnValue } = await program.execute(args, foreignCallHandler);
+  return returnValue as boolean;
+}
+```
+
+Now the `is_equal()` function and relevant types are readily available for use in TypeScript.