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| 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 prettyFormat from "pretty-format"; |
| 9 | +import { CompilerError, Effect } from ".."; |
| 10 | +import { |
| 11 | + HIRFunction, |
| 12 | + IdentifierId, |
| 13 | + Place, |
| 14 | + getHookKind, |
| 15 | + isUseOperator, |
| 16 | +} from "../HIR"; |
| 17 | +import { |
| 18 | + eachInstructionValueOperand, |
| 19 | + eachTerminalOperand, |
| 20 | +} from "../HIR/visitors"; |
| 21 | +import { isEffectHook } from "./ValidateMemoizedEffectDependencies"; |
| 22 | + |
| 23 | +/** |
| 24 | + * Validates that local variables cannot be reassigned after render. |
| 25 | + * This prevents a category of bugs in which a closure captures a |
| 26 | + * binding from one render but does not update |
| 27 | + */ |
| 28 | +export function validateLocalsNotReassignedAfterRender(fn: HIRFunction): void { |
| 29 | + const contextVariables = new Set<IdentifierId>(); |
| 30 | + const reassignment = getContextReassignment(fn, contextVariables, false); |
| 31 | + if (reassignment !== null) { |
| 32 | + CompilerError.throwInvalidJS({ |
| 33 | + reason: |
| 34 | + "Reassigning a variable after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead", |
| 35 | + description: |
| 36 | + reassignment.identifier.name !== null && |
| 37 | + reassignment.identifier.name.kind === "named" |
| 38 | + ? `Variable \`${reassignment.identifier.name.value}\` cannot be reassigned after render` |
| 39 | + : "", |
| 40 | + loc: reassignment.loc, |
| 41 | + }); |
| 42 | + } |
| 43 | +} |
| 44 | + |
| 45 | +function getContextReassignment( |
| 46 | + fn: HIRFunction, |
| 47 | + contextVariables: Set<IdentifierId>, |
| 48 | + isFunctionExpression: boolean |
| 49 | +): Place | null { |
| 50 | + const reassigningFunctions = new Map<IdentifierId, Place>(); |
| 51 | + for (const [, block] of fn.body.blocks) { |
| 52 | + for (const instr of block.instructions) { |
| 53 | + const { lvalue, value } = instr; |
| 54 | + switch (value.kind) { |
| 55 | + case "FunctionExpression": |
| 56 | + case "ObjectMethod": { |
| 57 | + let reassignment = getContextReassignment( |
| 58 | + value.loweredFunc.func, |
| 59 | + contextVariables, |
| 60 | + true |
| 61 | + ); |
| 62 | + if (reassignment === null) { |
| 63 | + // If the function itself doesn't reassign, does one of its dependencies? |
| 64 | + for (const operand of eachInstructionValueOperand(value)) { |
| 65 | + const reassignmentFromOperand = reassigningFunctions.get( |
| 66 | + operand.identifier.id |
| 67 | + ); |
| 68 | + if (reassignmentFromOperand !== undefined) { |
| 69 | + reassignment = reassignmentFromOperand; |
| 70 | + break; |
| 71 | + } |
| 72 | + } |
| 73 | + } |
| 74 | + // if the function or its depends reassign, propagate that fact on the lvalue |
| 75 | + if (reassignment !== null) { |
| 76 | + reassigningFunctions.set(lvalue.identifier.id, reassignment); |
| 77 | + } |
| 78 | + break; |
| 79 | + } |
| 80 | + case "StoreLocal": { |
| 81 | + const reassignment = reassigningFunctions.get( |
| 82 | + value.value.identifier.id |
| 83 | + ); |
| 84 | + if (reassignment !== undefined) { |
| 85 | + reassigningFunctions.set( |
| 86 | + value.lvalue.place.identifier.id, |
| 87 | + reassignment |
| 88 | + ); |
| 89 | + reassigningFunctions.set(lvalue.identifier.id, reassignment); |
| 90 | + } |
| 91 | + break; |
| 92 | + } |
| 93 | + case "LoadLocal": { |
| 94 | + const reassignment = reassigningFunctions.get( |
| 95 | + value.place.identifier.id |
| 96 | + ); |
| 97 | + if (reassignment !== undefined) { |
| 98 | + reassigningFunctions.set(lvalue.identifier.id, reassignment); |
| 99 | + } |
| 100 | + break; |
| 101 | + } |
| 102 | + case "DeclareContext": { |
| 103 | + if (!isFunctionExpression) { |
| 104 | + contextVariables.add(value.lvalue.place.identifier.id); |
| 105 | + } |
| 106 | + break; |
| 107 | + } |
| 108 | + case "StoreContext": { |
| 109 | + if (isFunctionExpression) { |
| 110 | + if (contextVariables.has(value.lvalue.place.identifier.id)) { |
| 111 | + return value.lvalue.place; |
| 112 | + } |
| 113 | + } else { |
| 114 | + // We only track reassignments of variables defined in the outer |
| 115 | + // component or hook. |
| 116 | + contextVariables.add(value.lvalue.place.identifier.id); |
| 117 | + } |
| 118 | + break; |
| 119 | + } |
| 120 | + default: { |
| 121 | + for (const operand of eachInstructionValueOperand(value)) { |
| 122 | + CompilerError.invariant(operand.effect !== Effect.Unknown, { |
| 123 | + reason: `Expected effects to be inferred prior to ValidateLocalsNotReassignedAfterRender`, |
| 124 | + loc: operand.loc, |
| 125 | + }); |
| 126 | + const reassignment = reassigningFunctions.get( |
| 127 | + operand.identifier.id |
| 128 | + ); |
| 129 | + if ( |
| 130 | + reassignment !== undefined && |
| 131 | + operand.effect === Effect.Freeze |
| 132 | + ) { |
| 133 | + // Functions that reassign local variables are inherently mutable and are unsafe to pass |
| 134 | + // to a place that expects a frozen value. Propagate the reassignment upward. |
| 135 | + return reassignment; |
| 136 | + } |
| 137 | + } |
| 138 | + break; |
| 139 | + } |
| 140 | + } |
| 141 | + } |
| 142 | + for (const operand of eachTerminalOperand(block.terminal)) { |
| 143 | + const reassignment = reassigningFunctions.get(operand.identifier.id); |
| 144 | + if (reassignment !== undefined) { |
| 145 | + return reassignment; |
| 146 | + } |
| 147 | + } |
| 148 | + } |
| 149 | + return null; |
| 150 | +} |
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