init commit

backend/node_modules/@jridgewell/gen-mapping/src/set-array.ts

@@ -0,0 +1,82 @@
+type Key = string | number | symbol;
+
+/**
+ * SetArray acts like a `Set` (allowing only one occurrence of a string `key`), but provides the
+ * index of the `key` in the backing array.
+ *
+ * This is designed to allow synchronizing a second array with the contents of the backing array,
+ * like how in a sourcemap `sourcesContent[i]` is the source content associated with `source[i]`,
+ * and there are never duplicates.
+ */
+export class SetArray<T extends Key = Key> {
+  declare private _indexes: Record<T, number | undefined>;
+  declare array: readonly T[];
+
+  constructor() {
+    this._indexes = { __proto__: null } as any;
+    this.array = [];
+  }
+}
+
+interface PublicSet<T extends Key> {
+  array: T[];
+  _indexes: SetArray<T>['_indexes'];
+}
+
+/**
+ * Typescript doesn't allow friend access to private fields, so this just casts the set into a type
+ * with public access modifiers.
+ */
+function cast<T extends Key>(set: SetArray<T>): PublicSet<T> {
+  return set as any;
+}
+
+/**
+ * Gets the index associated with `key` in the backing array, if it is already present.
+ */
+export function get<T extends Key>(setarr: SetArray<T>, key: T): number | undefined {
+  return cast(setarr)._indexes[key];
+}
+
+/**
+ * Puts `key` into the backing array, if it is not already present. Returns
+ * the index of the `key` in the backing array.
+ */
+export function put<T extends Key>(setarr: SetArray<T>, key: T): number {
+  // The key may or may not be present. If it is present, it's a number.
+  const index = get(setarr, key);
+  if (index !== undefined) return index;
+
+  const { array, _indexes: indexes } = cast(setarr);
+
+  const length = array.push(key);
+  return (indexes[key] = length - 1);
+}
+
+/**
+ * Pops the last added item out of the SetArray.
+ */
+export function pop<T extends Key>(setarr: SetArray<T>): void {
+  const { array, _indexes: indexes } = cast(setarr);
+  if (array.length === 0) return;
+
+  const last = array.pop()!;
+  indexes[last] = undefined;
+}
+
+/**
+ * Removes the key, if it exists in the set.
+ */
+export function remove<T extends Key>(setarr: SetArray<T>, key: T): void {
+  const index = get(setarr, key);
+  if (index === undefined) return;
+
+  const { array, _indexes: indexes } = cast(setarr);
+  for (let i = index + 1; i < array.length; i++) {
+    const k = array[i];
+    array[i - 1] = k;
+    indexes[k]!--;
+  }
+  indexes[key] = undefined;
+  array.pop();
+}