Add utility to convert AST in easier to process data structures (#20)

util/convert-ast.ts

@@ -0,0 +1,71 @@
+import * as ts from 'typescript';
+
+/** Wraps an AST node. Can be used as a tree using `children` or a linked list using `next` and `skip`. */
+export interface NodeWrap {
+    /** The real AST node. */
+    node: ts.Node;
+    /** All immediate children of `node` that would be visited by `ts.forEachChild(node, cb)`. */
+    children: NodeWrap[];
+    /** Link to the next NodeWrap, depth-first. */
+    next?: NodeWrap;
+    /** Link to the next NodeWrap skipping all children of the current node. */
+    skip?: NodeWrap;
+    /** Link to the parent NodeWrap */
+    parent?: NodeWrap;
+}
+
+export interface ConvertedAst {
+    /** nodes wrapped in a data structure with useful links */
+    wrapped: NodeWrap;
+    /** depth-first array of all nodes */
+    flat: ReadonlyArray<ts.Node>;
+}
+
+/**
+ * Takes a `ts.SourceFile` and creates data structures that are easier (or more performant) to traverse.
+ * Note that there is only a performance gain if you can reuse these structures. It's not recommended for one-time AST walks.
+ */
+export function convertAst(sourceFile: ts.SourceFile): ConvertedAst {
+    const wrapped: NodeWrap = {
+        node: sourceFile,
+        parent: undefined,
+        children: [],
+        next: undefined,
+        skip: undefined,
+    };
+    const flat: ts.Node[] = [];
+    let current = wrapped;
+    let previous = current;
+    ts.forEachChild(sourceFile, function wrap(node) {
+        flat.push(node);
+        const parent = current;
+        previous.next = current = {
+            node,
+            parent,
+            children: [],
+            next: undefined,
+            skip: undefined,
+        };
+        if (previous !== parent)
+            setSkip(previous, current);
+
+        previous = current;
+        parent.children.push(current);
+
+        ts.forEachChild(node, wrap);
+
+        current = parent;
+    });
+
+    return {
+        wrapped,
+        flat,
+    };
+}
+
+function setSkip(node: NodeWrap, skip: NodeWrap) {
+    do {
+        node.skip = skip;
+        node = node.parent!;
+    } while (node !== skip.parent);
+}

util/index.ts

@@ -2,3 +2,4 @@ export * from './util';
 export * from './usage';
 export * from './control-flow';
 export * from './type';
+export * from './convert-ast';