feat(type assertions): support type assertions

I.e. `const a = <B>c;` --> `const a = c as B;`

README.md

@@ -21,7 +21,7 @@ This is a simple tool to migrate full-fledged TypeScript code to type-annotated
 | Number Enum                                 | ✅     |                                                                |
 | String Enum                                 | ✅     |                                                                |
 | Const Enum                                  | ✅     |                                                                |
-| Type assertion expressions                  | ❌     | I.e. `<string>value` --> `value as string`                     |
+| Type assertion expressions                  | ✅     | I.e. `<string>value` --> `value as string`                     |
 | Namespaces                                  | ❌     | This might turn out to be impossible to do, to be investigated |
 | Rewrite file extensions in import specifier | ❌     | This might be included with an option in the future            |
 

src/transform.spec.ts

@@ -388,6 +388,12 @@ await describe('transform', async () => {
       );
     });
   });
+
+  await describe('type assertions', async () => {
+    await it('should transform a type assertion', async () => {
+      await scenario(`const foo = <a>'foo';`, `const foo = 'foo' as a;`);
+    });
+  });
 });
 
 async function scenario(

src/transform.ts

@@ -40,6 +40,10 @@ export function transform(
       changed ||= result.changed;
       resultingNode = result.node;
     }
+    if (ts.isTypeAssertionExpression(node)) {
+      resultingNode = ts.factory.createAsExpression(node.expression, node.type);
+      changed = true;
+    }
     if (Array.isArray(resultingNode)) {
       return resultingNode.map((node) =>
         ts.visitEachChild(node, transformNode, undefined),