1. /**

  2.  * Copyright (c) Meta Platforms, Inc. and affiliates.

  3.  *

  4.  * This source code is licensed under the MIT license found in the

  5.  * LICENSE file in the root directory of this source tree.

  6.  *

  7.  * @flow

  8.  */

  9. 

  10. import type {Fiber} from './ReactInternalTypes';

  11. 

  12. export type StackCursor<T> = {current: T};

  13. 

  14. const valueStack: Array<any> = [];

  15. 

  16. let fiberStack: Array<Fiber | null>;

  17. 

  18. if (__DEV__) {

  19.   fiberStack = [];

  20. }

  21. 

  22. let index = -1;

  23. 

  24. function createCursor<T>(defaultValue: T): StackCursor<T> {

  25.   return {

  26.     current: defaultValue,

  27.   };

  28. }

  29. 

  30. function isEmpty(): boolean {

  31.   return index === -1;

  32. }

  33. 

  34. function pop<T>(cursor: StackCursor<T>, fiber: Fiber): void {

  35.   if (index < 0) {

  36.     if (__DEV__) {

  37.       console.error('Unexpected pop.');

  38.     }

  39.     return;

  40.   }

  41. 

  42.   if (__DEV__) {

  43.     if (fiber !== fiberStack[index]) {

  44.       console.error('Unexpected Fiber popped.');

  45.     }

  46.   }

  47. 

  48.   cursor.current = valueStack[index];

  49. 

  50.   valueStack[index] = null;

  51. 

  52.   if (__DEV__) {

  53.     fiberStack[index] = null;

  54.   }

  55. 

  56.   index--;

  57. }

  58. 

  59. function push<T>(cursor: StackCursor<T>, value: T, fiber: Fiber): void {

  60.   index++;

  61. 

  62.   valueStack[index] = cursor.current;

  63. 

  64.   if (__DEV__) {

  65.     fiberStack[index] = fiber;

  66.   }

  67. 

  68.   cursor.current = value;

  69. }

  70. 

  71. function checkThatStackIsEmpty() {

  72.   if (__DEV__) {

  73.     if (index !== -1) {

  74.       console.error(

  75.         'Expected an empty stack. Something was not reset properly.',

  76.       );

  77.     }

  78.   }

  79. }

  80. 

  81. function resetStackAfterFatalErrorInDev() {

  82.   if (__DEV__) {

  83.     index = -1;

  84.     valueStack.length = 0;

  85.     fiberStack.length = 0;

  86.   }

  87. }

  88. 

  89. export {

  90.   createCursor,

  91.   isEmpty,

  92.   pop,

  93.   push,

  94.   // DEV only:

  95.   checkThatStackIsEmpty,

  96.   resetStackAfterFatalErrorInDev,

  97. };
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