| 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 { |
| 9 | CompilerDiagnostic, |
| 10 | CompilerError, |
| 11 | ErrorCategory, |
| 12 | } from '../CompilerError'; |
| 13 | import { |
| 14 | FunctionExpression, |
| 15 | HIRFunction, |
| 16 | IdentifierId, |
| 17 | SourceLocation, |
| 18 | } from '../HIR'; |
| 19 | import {Environment} from '../HIR/Environment'; |
| 20 | import { |
| 21 | eachInstructionValueOperand, |
| 22 | eachTerminalOperand, |
| 23 | } from '../HIR/visitors'; |
| 24 | |
| 25 | export function validateUseMemo(fn: HIRFunction): void { |
| 26 | const voidMemoErrors = new CompilerError(); |
| 27 | const useMemos = new Set<IdentifierId>(); |
| 28 | const react = new Set<IdentifierId>(); |
| 29 | const functions = new Map<IdentifierId, FunctionExpression>(); |
| 30 | const unusedUseMemos = new Map<IdentifierId, SourceLocation>(); |
| 31 | for (const [, block] of fn.body.blocks) { |
| 32 | for (const {lvalue, value} of block.instructions) { |
| 33 | if (unusedUseMemos.size !== 0) { |
| 34 | /** |
| 35 | * Most of the time useMemo results are referenced immediately. Don't bother |
| 36 | * scanning instruction operands for useMemos unless there is an as-yet-unused |
| 37 | * useMemo. |
| 38 | */ |
| 39 | for (const operand of eachInstructionValueOperand(value)) { |
| 40 | unusedUseMemos.delete(operand.identifier.id); |
| 41 | } |
| 42 | } |
| 43 | switch (value.kind) { |
| 44 | case 'LoadGlobal': { |
| 45 | if (value.binding.name === 'useMemo') { |
| 46 | useMemos.add(lvalue.identifier.id); |
| 47 | } else if (value.binding.name === 'React') { |
| 48 | react.add(lvalue.identifier.id); |
| 49 | } |
| 50 | break; |
| 51 | } |
| 52 | case 'PropertyLoad': { |
| 53 | if (react.has(value.object.identifier.id)) { |
| 54 | if (value.property === 'useMemo') { |
| 55 | useMemos.add(lvalue.identifier.id); |
| 56 | } |
| 57 | } |
| 58 | break; |
| 59 | } |
| 60 | case 'FunctionExpression': { |
| 61 | functions.set(lvalue.identifier.id, value); |
| 62 | break; |
| 63 | } |
| 64 | case 'MethodCall': |
| 65 | case 'CallExpression': { |
| 66 | // Is the function being called useMemo, with at least 1 argument? |
| 67 | const callee = |
| 68 | value.kind === 'CallExpression' ? value.callee : value.property; |
| 69 | const isUseMemo = useMemos.has(callee.identifier.id); |
| 70 | if (!isUseMemo || value.args.length === 0) { |
| 71 | continue; |
| 72 | } |
| 73 | |
| 74 | /* |
| 75 | * If yes get the first argument and if it refers to a locally defined function |
| 76 | * expression, validate the function |
| 77 | */ |
| 78 | const [arg] = value.args; |
| 79 | if (arg.kind !== 'Identifier') { |
| 80 | continue; |
| 81 | } |
| 82 | const body = functions.get(arg.identifier.id); |
| 83 | if (body === undefined) { |
| 84 | continue; |
| 85 | } |
| 86 | |
| 87 | if (body.loweredFunc.func.params.length > 0) { |
| 88 | const firstParam = body.loweredFunc.func.params[0]; |
| 89 | const loc = |
| 90 | firstParam.kind === 'Identifier' |
| 91 | ? firstParam.loc |
| 92 | : firstParam.place.loc; |
| 93 | fn.env.recordError( |
| 94 | CompilerDiagnostic.create({ |
| 95 | category: ErrorCategory.UseMemo, |
| 96 | reason: 'useMemo() callbacks may not accept parameters', |
| 97 | description: |
| 98 | 'useMemo() callbacks are called by React to cache calculations across re-renders. They should not take parameters. Instead, directly reference the props, state, or local variables needed for the computation', |
| 99 | suggestions: null, |
| 100 | }).withDetails({ |
| 101 | kind: 'error', |
| 102 | loc, |
| 103 | message: 'Callbacks with parameters are not supported', |
| 104 | }), |
| 105 | ); |
| 106 | } |
| 107 | |
| 108 | if (body.loweredFunc.func.async || body.loweredFunc.func.generator) { |
| 109 | fn.env.recordError( |
| 110 | CompilerDiagnostic.create({ |
| 111 | category: ErrorCategory.UseMemo, |
| 112 | reason: |
| 113 | 'useMemo() callbacks may not be async or generator functions', |
| 114 | description: |
| 115 | 'useMemo() callbacks are called once and must synchronously return a value', |
| 116 | suggestions: null, |
| 117 | }).withDetails({ |
| 118 | kind: 'error', |
| 119 | loc: body.loc, |
| 120 | message: 'Async and generator functions are not supported', |
| 121 | }), |
| 122 | ); |
| 123 | } |
| 124 | |
| 125 | validateNoContextVariableAssignment(body.loweredFunc.func, fn.env); |
| 126 | |
| 127 | if (fn.env.config.validateNoVoidUseMemo) { |
| 128 | if (!hasNonVoidReturn(body.loweredFunc.func)) { |
| 129 | voidMemoErrors.pushDiagnostic( |
| 130 | CompilerDiagnostic.create({ |
| 131 | category: ErrorCategory.VoidUseMemo, |
| 132 | reason: 'useMemo() callbacks must return a value', |
| 133 | description: `This useMemo() callback doesn't return a value. useMemo() is for computing and caching values, not for arbitrary side effects`, |
| 134 | suggestions: null, |
| 135 | }).withDetails({ |
| 136 | kind: 'error', |
| 137 | loc: body.loc, |
| 138 | message: 'useMemo() callbacks must return a value', |
| 139 | }), |
| 140 | ); |
| 141 | } else { |
| 142 | unusedUseMemos.set(lvalue.identifier.id, callee.loc); |
| 143 | } |
| 144 | } |
| 145 | break; |
| 146 | } |
| 147 | } |
| 148 | } |
| 149 | if (unusedUseMemos.size !== 0) { |
| 150 | for (const operand of eachTerminalOperand(block.terminal)) { |
| 151 | unusedUseMemos.delete(operand.identifier.id); |
| 152 | } |
| 153 | } |
| 154 | } |
| 155 | if (unusedUseMemos.size !== 0) { |
| 156 | /** |
| 157 | * Basic check for unused memos, where the result of the call is never referenced. This runs |
| 158 | * before DCE so it's more of an AST-level check that something, _anything_, cares about the value. |
| 159 | * |
| 160 | * This is easy to defeat with e.g. `const _ = useMemo(...)` but it at least gives us something to teach. |
| 161 | * Even a DCE-based version could be bypassed with `noop(useMemo(...))`. |
| 162 | */ |
| 163 | for (const loc of unusedUseMemos.values()) { |
| 164 | voidMemoErrors.pushDiagnostic( |
| 165 | CompilerDiagnostic.create({ |
| 166 | category: ErrorCategory.VoidUseMemo, |
| 167 | reason: 'useMemo() result is unused', |
| 168 | description: `This useMemo() value is unused. useMemo() is for computing and caching values, not for arbitrary side effects`, |
| 169 | suggestions: null, |
| 170 | }).withDetails({ |
| 171 | kind: 'error', |
| 172 | loc, |
| 173 | message: 'useMemo() result is unused', |
| 174 | }), |
| 175 | ); |
| 176 | } |
| 177 | } |
| 178 | fn.env.logErrors(voidMemoErrors.asResult()); |
| 179 | } |
| 180 | |
| 181 | function validateNoContextVariableAssignment( |
| 182 | fn: HIRFunction, |
| 183 | env: Environment, |
| 184 | ): void { |
| 185 | const context = new Set(fn.context.map(place => place.identifier.id)); |
| 186 | for (const block of fn.body.blocks.values()) { |
| 187 | for (const instr of block.instructions) { |
| 188 | const value = instr.value; |
| 189 | switch (value.kind) { |
| 190 | case 'StoreContext': { |
| 191 | if (context.has(value.lvalue.place.identifier.id)) { |
| 192 | env.recordError( |
| 193 | CompilerDiagnostic.create({ |
| 194 | category: ErrorCategory.UseMemo, |
| 195 | reason: |
| 196 | 'useMemo() callbacks may not reassign variables declared outside of the callback', |
| 197 | description: |
| 198 | 'useMemo() callbacks must be pure functions and cannot reassign variables defined outside of the callback function', |
| 199 | suggestions: null, |
| 200 | }).withDetails({ |
| 201 | kind: 'error', |
| 202 | loc: value.lvalue.place.loc, |
| 203 | message: 'Cannot reassign variable', |
| 204 | }), |
| 205 | ); |
| 206 | } |
| 207 | break; |
| 208 | } |
| 209 | } |
| 210 | } |
| 211 | } |
| 212 | } |
| 213 | |
| 214 | function hasNonVoidReturn(func: HIRFunction): boolean { |
| 215 | for (const [, block] of func.body.blocks) { |
| 216 | if (block.terminal.kind === 'return') { |
| 217 | if ( |
| 218 | block.terminal.returnVariant === 'Explicit' || |
| 219 | block.terminal.returnVariant === 'Implicit' |
| 220 | ) { |
| 221 | return true; |
| 222 | } |
| 223 | } |
| 224 | } |
| 225 | return false; |
| 226 | } |