| 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 | CallExpression, |
| 11 | getHookKind, |
| 12 | HIRFunction, |
| 13 | IdentifierId, |
| 14 | InstructionValue, |
| 15 | isArrayType, |
| 16 | isPlainObjectType, |
| 17 | isPrimitiveType, |
| 18 | isSetStateType, |
| 19 | isStartTransitionType, |
| 20 | LoadLocal, |
| 21 | StoreLocal, |
| 22 | } from '../HIR'; |
| 23 | import { |
| 24 | eachInstructionValueOperand, |
| 25 | eachTerminalOperand, |
| 26 | } from '../HIR/visitors'; |
| 27 | import {retainWhere} from '../Utils/utils'; |
| 28 | |
| 29 | /** |
| 30 | * Optimizes the code for running specifically in an SSR environment. This optimization |
| 31 | * asssumes that setState will not be called during render during initial mount, which |
| 32 | * allows inlining useState/useReducer. |
| 33 | * |
| 34 | * Optimizations: |
| 35 | * - Inline useState/useReducer |
| 36 | * - Remove effects |
| 37 | * - Remove refs where known to be unused during render (eg directly passed to a dom node) |
| 38 | * - Remove event handlers |
| 39 | * |
| 40 | * Note that an earlier pass already inlines useMemo/useCallback |
| 41 | */ |
| 42 | export function optimizeForSSR(fn: HIRFunction): void { |
| 43 | const inlinedState = new Map<IdentifierId, InstructionValue>(); |
| 44 | /** |
| 45 | * First pass identifies useState/useReducer which can be safely inlined. Any use |
| 46 | * of the hook return other than destructuring (with a specific pattern) prevents |
| 47 | * inlining. |
| 48 | * |
| 49 | * Supported cases: |
| 50 | * - `const [state, ] = useState( <primitive-array-or-object> )` |
| 51 | * - `const [state, ] = useReducer(..., <value>)` |
| 52 | * - `const [state, ] = useReducer[..., <value>, <init>]` |
| 53 | */ |
| 54 | for (const block of fn.body.blocks.values()) { |
| 55 | for (const instr of block.instructions) { |
| 56 | const {value} = instr; |
| 57 | switch (value.kind) { |
| 58 | case 'Destructure': { |
| 59 | if ( |
| 60 | inlinedState.has(value.value.identifier.id) && |
| 61 | value.lvalue.pattern.kind === 'ArrayPattern' && |
| 62 | value.lvalue.pattern.items.length >= 1 && |
| 63 | value.lvalue.pattern.items[0].kind === 'Identifier' |
| 64 | ) { |
| 65 | // Allow destructuring of inlined states |
| 66 | continue; |
| 67 | } |
| 68 | break; |
| 69 | } |
| 70 | case 'MethodCall': |
| 71 | case 'CallExpression': { |
| 72 | const calleee = |
| 73 | value.kind === 'CallExpression' ? value.callee : value.property; |
| 74 | const hookKind = getHookKind(fn.env, calleee.identifier); |
| 75 | switch (hookKind) { |
| 76 | case 'useReducer': { |
| 77 | if ( |
| 78 | value.args.length === 2 && |
| 79 | value.args[1].kind === 'Identifier' |
| 80 | ) { |
| 81 | const arg = value.args[1]; |
| 82 | const replace: LoadLocal = { |
| 83 | kind: 'LoadLocal', |
| 84 | place: arg, |
| 85 | loc: arg.loc, |
| 86 | }; |
| 87 | inlinedState.set(instr.lvalue.identifier.id, replace); |
| 88 | } else if ( |
| 89 | value.args.length === 3 && |
| 90 | value.args[1].kind === 'Identifier' && |
| 91 | value.args[2].kind === 'Identifier' |
| 92 | ) { |
| 93 | const arg = value.args[1]; |
| 94 | const initializer = value.args[2]; |
| 95 | const replace: CallExpression = { |
| 96 | kind: 'CallExpression', |
| 97 | callee: initializer, |
| 98 | args: [arg], |
| 99 | loc: value.loc, |
| 100 | }; |
| 101 | inlinedState.set(instr.lvalue.identifier.id, replace); |
| 102 | } |
| 103 | break; |
| 104 | } |
| 105 | case 'useState': { |
| 106 | if ( |
| 107 | value.args.length === 1 && |
| 108 | value.args[0].kind === 'Identifier' |
| 109 | ) { |
| 110 | const arg = value.args[0]; |
| 111 | if ( |
| 112 | isPrimitiveType(arg.identifier) || |
| 113 | isPlainObjectType(arg.identifier) || |
| 114 | isArrayType(arg.identifier) |
| 115 | ) { |
| 116 | const replace: LoadLocal = { |
| 117 | kind: 'LoadLocal', |
| 118 | place: arg, |
| 119 | loc: arg.loc, |
| 120 | }; |
| 121 | inlinedState.set(instr.lvalue.identifier.id, replace); |
| 122 | } |
| 123 | } |
| 124 | break; |
| 125 | } |
| 126 | } |
| 127 | } |
| 128 | } |
| 129 | // Any use of useState/useReducer return besides destructuring prevents inlining |
| 130 | if (inlinedState.size !== 0) { |
| 131 | for (const operand of eachInstructionValueOperand(value)) { |
| 132 | inlinedState.delete(operand.identifier.id); |
| 133 | } |
| 134 | } |
| 135 | } |
| 136 | if (inlinedState.size !== 0) { |
| 137 | for (const operand of eachTerminalOperand(block.terminal)) { |
| 138 | inlinedState.delete(operand.identifier.id); |
| 139 | } |
| 140 | } |
| 141 | } |
| 142 | for (const block of fn.body.blocks.values()) { |
| 143 | for (const instr of block.instructions) { |
| 144 | const {value} = instr; |
| 145 | switch (value.kind) { |
| 146 | case 'FunctionExpression': { |
| 147 | if (hasKnownNonRenderCall(value.loweredFunc.func)) { |
| 148 | instr.value = { |
| 149 | kind: 'Primitive', |
| 150 | value: undefined, |
| 151 | loc: value.loc, |
| 152 | }; |
| 153 | } |
| 154 | break; |
| 155 | } |
| 156 | case 'JsxExpression': { |
| 157 | if ( |
| 158 | value.tag.kind === 'BuiltinTag' && |
| 159 | value.tag.name.indexOf('-') === -1 |
| 160 | ) { |
| 161 | const tag = value.tag.name; |
| 162 | retainWhere(value.props, prop => { |
| 163 | return ( |
| 164 | prop.kind === 'JsxSpreadAttribute' || |
| 165 | (!isKnownEventHandler(tag, prop.name) && prop.name !== 'ref') |
| 166 | ); |
| 167 | }); |
| 168 | } |
| 169 | break; |
| 170 | } |
| 171 | case 'Destructure': { |
| 172 | if (inlinedState.has(value.value.identifier.id)) { |
| 173 | // Canonical check is part of determining if state can inline, this is for TS |
| 174 | CompilerError.invariant( |
| 175 | value.lvalue.pattern.kind === 'ArrayPattern' && |
| 176 | value.lvalue.pattern.items.length >= 1 && |
| 177 | value.lvalue.pattern.items[0].kind === 'Identifier', |
| 178 | { |
| 179 | reason: |
| 180 | 'Expected a valid destructuring pattern for inlined state', |
| 181 | message: 'Expected a valid destructuring pattern', |
| 182 | loc: value.loc, |
| 183 | }, |
| 184 | ); |
| 185 | const store: StoreLocal = { |
| 186 | kind: 'StoreLocal', |
| 187 | loc: value.loc, |
| 188 | type: null, |
| 189 | lvalue: { |
| 190 | kind: value.lvalue.kind, |
| 191 | place: value.lvalue.pattern.items[0], |
| 192 | }, |
| 193 | value: value.value, |
| 194 | }; |
| 195 | instr.value = store; |
| 196 | } |
| 197 | break; |
| 198 | } |
| 199 | case 'MethodCall': |
| 200 | case 'CallExpression': { |
| 201 | const calleee = |
| 202 | value.kind === 'CallExpression' ? value.callee : value.property; |
| 203 | const hookKind = getHookKind(fn.env, calleee.identifier); |
| 204 | switch (hookKind) { |
| 205 | case 'useEffectEvent': { |
| 206 | if ( |
| 207 | value.args.length === 1 && |
| 208 | value.args[0].kind === 'Identifier' |
| 209 | ) { |
| 210 | const load: LoadLocal = { |
| 211 | kind: 'LoadLocal', |
| 212 | place: value.args[0], |
| 213 | loc: value.loc, |
| 214 | }; |
| 215 | instr.value = load; |
| 216 | } |
| 217 | break; |
| 218 | } |
| 219 | case 'useEffect': |
| 220 | case 'useLayoutEffect': |
| 221 | case 'useInsertionEffect': { |
| 222 | // Drop effects |
| 223 | instr.value = { |
| 224 | kind: 'Primitive', |
| 225 | value: undefined, |
| 226 | loc: value.loc, |
| 227 | }; |
| 228 | break; |
| 229 | } |
| 230 | case 'useReducer': |
| 231 | case 'useState': { |
| 232 | const replace = inlinedState.get(instr.lvalue.identifier.id); |
| 233 | if (replace != null) { |
| 234 | instr.value = replace; |
| 235 | } |
| 236 | break; |
| 237 | } |
| 238 | } |
| 239 | } |
| 240 | } |
| 241 | } |
| 242 | } |
| 243 | } |
| 244 | |
| 245 | function hasKnownNonRenderCall(fn: HIRFunction): boolean { |
| 246 | for (const block of fn.body.blocks.values()) { |
| 247 | for (const instr of block.instructions) { |
| 248 | if ( |
| 249 | instr.value.kind === 'CallExpression' && |
| 250 | (isSetStateType(instr.value.callee.identifier) || |
| 251 | isStartTransitionType(instr.value.callee.identifier)) |
| 252 | ) { |
| 253 | return true; |
| 254 | } |
| 255 | } |
| 256 | } |
| 257 | return false; |
| 258 | } |
| 259 | |
| 260 | const EVENT_HANDLER_PATTERN = /^on[A-Z]/; |
| 261 | function isKnownEventHandler(_tag: string, prop: string): boolean { |
| 262 | return EVENT_HANDLER_PATTERN.test(prop); |
| 263 | } |