OptionalChainSidemap Type — react Architecture

Source Code

compiler/packages/babel-plugin-react-compiler/src/HIR/CollectOptionalChainDependencies.ts lines 48–115

export type OptionalChainSidemap = {
  /**
   * Stores the correct property mapping (e.g. `a?.b` instead of `a.b`) for
   * dependency calculation. Note that we currently do not store anything on
   * outer phi nodes.
   */
  temporariesReadInOptional: ReadonlyMap<IdentifierId, ReactiveScopeDependency>;
  /**
   * Records instructions (PropertyLoads, StoreLocals, and test terminals)
   * processed in this pass. When extracting dependencies in
   * PropagateScopeDependencies, these instructions are skipped.
   *
   * E.g. given a?.b
   * ```
   * bb0
   *   $0 = LoadLocal 'a'
   *   test $0 then=bb1         <- Avoid adding dependencies from these instructions, as
   * bb1                           the sidemap produced by readOptionalBlock already maps
   *   $1 = PropertyLoad $0.'b' <- $1 and $2 back to a?.b. Instead, we want to add a?.b
   *   StoreLocal $2 = $1       <- as a dependency when $1 or $2 are later used in either
   *                                 - an unhoistable expression within an outer optional
   *                                   block e.g. MethodCall
   *                                 - a phi node (if the entire optional value is hoistable)
   * ```
   *
   * Note that mapping blockIds to their evaluated dependency path does not
   * work, since values produced by inner optional chains may be referenced in
   * outer ones
   * ```
   * a?.b.c()
   *  ->
   * bb0
   *   $0 = LoadLocal 'a'
   *   test $0 then=bb1
   * bb1
   *   $1 = PropertyLoad $0.'b'
   *   StoreLocal $2 = $1
   *   goto bb2
   * bb2
   *   test $2 then=bb3
   * bb3:
   *   $3 = PropertyLoad $2.'c'
   *   StoreLocal $4 = $3
   *   goto bb4
   * bb4
   *   test $4 then=bb5
   * bb5:
   *   $5 = MethodCall $2.$4() <--- here, we want to take a dep on $2 and $4!
   * ```
   *
   * Also note that InstructionIds are not unique across inner functions.
   */
  processedInstrsInOptional: ReadonlySet<Instruction | Terminal>;
  /**
   * Records optional chains for which we can safely evaluate non-optional
   * PropertyLoads. e.g. given `a?.b.c`, we can evaluate any load from `a?.b` at
   * the optional terminal in bb1.
   * ```js
   * bb1:
   *   ...
   *   Optional optional=false test=bb2 fallth=...
   * bb2:
   *   Optional optional=true test=bb3 fallth=...
   * ...
   * ```
   */
  hoistableObjects: ReadonlyMap<BlockId, ReactiveScopeDependency>;
};