| 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 | |
| 8 | import {CompilerError} from '..'; |
| 9 | import { |
| 10 | convertHoistedLValueKind, |
| 11 | IdentifierId, |
| 12 | InstructionId, |
| 13 | InstructionKind, |
| 14 | Place, |
| 15 | ReactiveFunction, |
| 16 | ReactiveInstruction, |
| 17 | ReactiveScopeBlock, |
| 18 | ReactiveStatement, |
| 19 | } from '../HIR'; |
| 20 | import {empty, Stack} from '../Utils/Stack'; |
| 21 | import { |
| 22 | ReactiveFunctionTransform, |
| 23 | Transformed, |
| 24 | visitReactiveFunction, |
| 25 | } from './visitors'; |
| 26 | |
| 27 | /* |
| 28 | * Prunes DeclareContexts lowered for HoistedConsts, and transforms any references back to its |
| 29 | * original instruction kind. |
| 30 | * |
| 31 | * Also detects and bails out on context variables which are: |
| 32 | * - function declarations, which are hoisted by JS engines to the nearest block scope |
| 33 | * - referenced before they are defined (i.e. having a `DeclareContext HoistedConst`) |
| 34 | * - declared |
| 35 | * |
| 36 | * This is because React Compiler converts a `function foo()` function declaration to |
| 37 | * 1. a `let foo;` declaration before reactive memo blocks |
| 38 | * 2. a `foo = function foo() {}` assignment within the block |
| 39 | * |
| 40 | * This means references before the assignment are invalid (see fixture |
| 41 | * error.todo-functiondecl-hoisting) |
| 42 | */ |
| 43 | export function pruneHoistedContexts(fn: ReactiveFunction): void { |
| 44 | visitReactiveFunction(fn, new Visitor(), { |
| 45 | activeScopes: empty(), |
| 46 | uninitialized: new Map(), |
| 47 | }); |
| 48 | } |
| 49 | |
| 50 | type VisitorState = { |
| 51 | activeScopes: Stack<Set<IdentifierId>>; |
| 52 | uninitialized: Map< |
| 53 | IdentifierId, |
| 54 | | { |
| 55 | kind: 'unknown-kind'; |
| 56 | } |
| 57 | | { |
| 58 | kind: 'func'; |
| 59 | definition: Place | null; |
| 60 | } |
| 61 | >; |
| 62 | }; |
| 63 | |
| 64 | class Visitor extends ReactiveFunctionTransform<VisitorState> { |
| 65 | override visitScope(scope: ReactiveScopeBlock, state: VisitorState): void { |
| 66 | state.activeScopes = state.activeScopes.push( |
| 67 | new Set(scope.scope.declarations.keys()), |
| 68 | ); |
| 69 | /** |
| 70 | * Add declared but not initialized / assigned variables. This may include |
| 71 | * function declarations that escape the memo block. |
| 72 | */ |
| 73 | for (const decl of scope.scope.declarations.values()) { |
| 74 | state.uninitialized.set(decl.identifier.id, {kind: 'unknown-kind'}); |
| 75 | } |
| 76 | this.traverseScope(scope, state); |
| 77 | state.activeScopes.pop(); |
| 78 | for (const decl of scope.scope.declarations.values()) { |
| 79 | state.uninitialized.delete(decl.identifier.id); |
| 80 | } |
| 81 | } |
| 82 | override visitPlace( |
| 83 | _id: InstructionId, |
| 84 | place: Place, |
| 85 | state: VisitorState, |
| 86 | ): void { |
| 87 | const maybeHoistedFn = state.uninitialized.get(place.identifier.id); |
| 88 | if ( |
| 89 | maybeHoistedFn?.kind === 'func' && |
| 90 | maybeHoistedFn.definition !== place |
| 91 | ) { |
| 92 | CompilerError.throwTodo({ |
| 93 | reason: '[PruneHoistedContexts] Rewrite hoisted function references', |
| 94 | loc: place.loc, |
| 95 | }); |
| 96 | } |
| 97 | } |
| 98 | override transformInstruction( |
| 99 | instruction: ReactiveInstruction, |
| 100 | state: VisitorState, |
| 101 | ): Transformed<ReactiveStatement> { |
| 102 | /** |
| 103 | * Remove hoisted declarations to preserve TDZ |
| 104 | */ |
| 105 | if (instruction.value.kind === 'DeclareContext') { |
| 106 | const maybeNonHoisted = convertHoistedLValueKind( |
| 107 | instruction.value.lvalue.kind, |
| 108 | ); |
| 109 | if (maybeNonHoisted != null) { |
| 110 | if ( |
| 111 | maybeNonHoisted === InstructionKind.Function && |
| 112 | state.uninitialized.has(instruction.value.lvalue.place.identifier.id) |
| 113 | ) { |
| 114 | state.uninitialized.set( |
| 115 | instruction.value.lvalue.place.identifier.id, |
| 116 | { |
| 117 | kind: 'func', |
| 118 | definition: null, |
| 119 | }, |
| 120 | ); |
| 121 | } |
| 122 | return {kind: 'remove'}; |
| 123 | } |
| 124 | } |
| 125 | if ( |
| 126 | instruction.value.kind === 'StoreContext' && |
| 127 | instruction.value.lvalue.kind !== InstructionKind.Reassign |
| 128 | ) { |
| 129 | /** |
| 130 | * Rewrite StoreContexts let/const that will be pre-declared in |
| 131 | * codegen to reassignments. |
| 132 | */ |
| 133 | const lvalueId = instruction.value.lvalue.place.identifier.id; |
| 134 | const isDeclaredByScope = state.activeScopes.find(scope => |
| 135 | scope.has(lvalueId), |
| 136 | ); |
| 137 | if (isDeclaredByScope) { |
| 138 | if ( |
| 139 | instruction.value.lvalue.kind === InstructionKind.Let || |
| 140 | instruction.value.lvalue.kind === InstructionKind.Const |
| 141 | ) { |
| 142 | instruction.value.lvalue.kind = InstructionKind.Reassign; |
| 143 | } else if (instruction.value.lvalue.kind === InstructionKind.Function) { |
| 144 | const maybeHoistedFn = state.uninitialized.get(lvalueId); |
| 145 | if (maybeHoistedFn != null) { |
| 146 | CompilerError.invariant(maybeHoistedFn.kind === 'func', { |
| 147 | reason: '[PruneHoistedContexts] Unexpected hoisted function', |
| 148 | loc: instruction.loc, |
| 149 | }); |
| 150 | maybeHoistedFn.definition = instruction.value.lvalue.place; |
| 151 | /** |
| 152 | * References to hoisted functions are now "safe" as variable assignments |
| 153 | * have finished. |
| 154 | */ |
| 155 | state.uninitialized.delete(lvalueId); |
| 156 | } |
| 157 | } else { |
| 158 | CompilerError.throwTodo({ |
| 159 | reason: '[PruneHoistedContexts] Unexpected kind', |
| 160 | description: `(${instruction.value.lvalue.kind})`, |
| 161 | loc: instruction.loc, |
| 162 | }); |
| 163 | } |
| 164 | } |
| 165 | } |
| 166 | |
| 167 | this.visitInstruction(instruction, state); |
| 168 | return {kind: 'keep'}; |
| 169 | } |
| 170 | } |