Update documentation in regard to new Babel macro

README.md

@@ -10,20 +10,27 @@ interfaces. It allows validating data, such as parsed JSON objects received
 over the network, or parsed JSON or YAML files, to check if they satisfy a
 TypeScript interface, and to produce informative error messages if they do not.
 
+This package works together with [ts-interface-checker](https://github.com/gristlabs/ts-interface-checker).
+You use `ts-interface-builder` in a build step that generates code for a runtime description of your interfaces.
+You then use `ts-interface-checker` in your code to create validator functions from this runtime description.
+
+These runtime descriptions come in the form of `ts-interface-checker` ["type suites"](https://github.com/gristlabs/ts-interface-checker#type-suites),
+one per input TS file.
+
+This package offers two ways to get generated "type suites" in your code:
+1. CLI - Run a command to save generated type suites in new TS or JS files
+2. Babel Macro *(advanced)* - Call a Babel macro function that returns a generated type suite
+
 ## Installation
 
 ```
 npm install --save-dev ts-interface-builder
 npm install --save ts-interface-checker
 ```
 
-## Usage
+## CLI Usage
 
-This module works together with [ts-interface-checker](https://github.com/gristlabs/ts-interface-checker) module. You use
-`ts-interface-builder` in a build step that converts some TypeScript interfaces
-to a new TypeScript or JavaScript file (with `-ti.ts` or `-ti.js` extension) that provides a runtime
-description of the interface. You then use `ts-interface-checker` in your
-program to create validator functions from this runtime description.
+**Run a command to save generated type suites in new TS or JS files**
 
 ```
 `npm bin`/ts-interface-builder [options] <typescript-files...>
@@ -53,7 +60,7 @@ import * as t from "ts-interface-checker";
 
 export const Square = t.iface([], {
   "size": "number",
-  "color": t.opt("string"),
+  "color": t.opt("string")
 });
 
 const exportedTypeSuite: t.ITypeSuite = {
@@ -62,7 +69,65 @@ const exportedTypeSuite: t.ITypeSuite = {
 export default exportedTypeSuite;
 ```
 
-See [ts-interface-checker](https://github.com/gristlabs/ts-interface-checker) module for how to use this file in your program.
+See [ts-interface-checker documentation](https://github.com/gristlabs/ts-interface-checker#readme) for how to use the exported type suite in your code.
+
+## Babel Macro Usage
+
+**Call a Babel macro function that returns a generated type suite**
+
+This method requires your project to have [Babel](https://babeljs.io/docs/en/) and [`babel-plugin-macros`](https://github.com/kentcdodds/babel-plugin-macros) set up.
+See installation instructions for each in their respective documentation.
+Note that if you're using a Babel preset, you might unknowingly already have `babel-plugin-macros` set up.
+For example, the popular [`babel-preset-react-app`](https://github.com/facebook/create-react-app/tree/master/packages/babel-preset-react-app)
+already includes `babel-plugin-macros`.
+
+With those things set up, in your code you can now just call the `getTypeSuite` macro function (exported from `ts-interface-builder/macro`) to get a type suite.
+During your Babel build step, the required type suites will be generated and included in Babel's output.
+
+For example, if you have a TypeScript file that defines some types:
+```typescript
+// foo.ts
+interface Square {
+  size: number;
+  color?: string;
+}
+```
+
+You can get a type suite for it in your code like this:
+```typescript
+import { getTypeSuite } from 'ts-interface-builder/macro';
+
+const fooTypeSuite = getTypeSuite('./foo.ts', { /* options */ });
+```
+
+The code above would be transpiled into:
+```js
+import * as t from "ts-interface-checker";
+
+function once(fn) {
+  var result;
+  return function () {
+    return result || (result = fn());
+  };
+}
+
+var typeSuite0 = once(function () {
+  return {
+    Square: t.iface([], {
+      "size": "number",
+      "color": t.opt("string")
+    })
+  };
+});
+
+var fooTypeSuite = typeSuite0();
+```
+
+See [ts-interface-checker documentation](https://github.com/gristlabs/ts-interface-checker#readme) for how to use the returned type suite in your code.
+
+The `getCheckers` macro function is also exported, as a convenience, to get a checker suite (with validator functions) directly
+instead of first getting a type suite and then creating a checker suite from it (using `ts-interface-checker`s `createCheckers` function). 
+As with `getTypeSuite`, repeated calls to `getCheckers` using the same arguments will return the same object.
 
 ## Limitations
 This module currently does not support generics, except Promises. Promises are supported by unwrapping `Promise<T>` to simply `T`.

lib/macro.ts

@@ -30,7 +30,7 @@ const macroHandler: MacroHandler = (params) => {
   if (!somePath) {
     return;
   }
-  const programPath = somePath.findParent((path) => path.isProgram());
+  const programPath = somePath.findParent((path) => path.isProgram())!;
 
   const registry = new RequirementRegistry();
   const toReplace = [