Codegen

Codegen is a library that creates, decorates or modifies DST objects in specific repeatable ways. This library is a common place for logic around how new nodes in a DST tree get created, as well as how to handle the whitespace and comments related to those nodes and the elements around them. Any function that creates a new node for insertion into the tree should be added here. When implementing functions for this library, the following rules should apply:

1. Any DST objects (expressions, statements, nodes, etc.) that are consumed as inputs should be defensively cloned before returning them as part of an output. There is a small execution cost to this, but if an object is duplicated anywhere in the tree, a runtime panic will occur.
2. Please add a comment header about what the output of your function is and what it does. After a while, it gets very hard to interpret what they do.
3. Unit tests can be very basic since the generated objects are going to be covered in many ways by the end to end tests. However, if a node gets returns that is invalid, it will fail to reneder and may result in a panic, which is not an acceptable outcome. A test to verify that the output is what we expect is a good safegard.