Cloning a TypeScript compiler API node.

getDeepMutableClone.ts

// one way...

function getDeepMutableClone<T extends ts.Node>(node: T): T {
    return ts.transform(node, [
        context => node => deepCloneWithContext(node, context)
    ]).transformed[0];

    function deepCloneWithContext<T extends ts.Node>(
        node: T,
        context: ts.TransformationContext
    ): T {
        const clonedNode = ts.visitEachChild(
            stripRanges(ts.getMutableClone(node)),
            child => deepCloneWithContext(child, context),
            context
        );
        clonedNode.parent = undefined as any;
        ts.forEachChild(clonedNode, child => { child.parent = clonedNode; });
        return clonedNode;
    }
}
  
// another way...

function getDeepMutableClone<T extends ts.Node>(node: T): T {
    return cloneWithParent(node, undefined);

    function cloneWithParent<T extends ts.Node>(node: T, parent: ts.Node | undefined) {
        const clone = stripRanges(ts.getMutableClone(node));
        clone.parent = parent as ts.Node;

        for (const propName of Object.keys(clone)) {
            if (propName === "parent" || propName === "original")
                continue;

            const propValue = clone[propName];
            if (propValue instanceof Array) {
                if (propValue.length > 0 && isNode(propValue[0])) {
                    clone[propName] = propValue.map(child => cloneWithParent(child, clone));
                }
            }
            else if (isNode(propValue)) {
                clone[propName] = cloneWithParent(propValue, clone);
            }
        }

        return clone;
    }
}

// common
  
function isNode(value: any): value is ts.Node {
    return value != null
        && typeof value.pos === "number"
        && typeof value.end === "number"
        && typeof value.kind === "number";
}
  
// See https://stackoverflow.com/a/57367717/188246 for
// why this is necessary.
function stripRanges<T extends ts.Node>(node: T) {
    node.pos = -1;
    node.end = -1;
    return node;
}