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fix: defer lookaheadState to Babel 8 #13383

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fix: defer lookaheadState to Babel 8 #13383

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36 changes: 24 additions & 12 deletions packages/babel-parser/src/tokenizer/index.js
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Expand Up @@ -182,17 +182,29 @@ export default class Tokenizer extends ParserErrors {
* @memberof Tokenizer
*/
createLookaheadState(state: State): LookaheadState {
return {
pos: state.pos,
value: null,
type: state.type,
start: state.start,
end: state.end,
lastTokEnd: state.end,
context: [this.curContext()],
exprAllowed: state.exprAllowed,
inType: state.inType,
};
if (process.env.BABEL_8_BREAKING) {
const { pos, type, start, end, exprAllowed, inType } = state;
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Use destructuring here to avoid double object access (state.end) and redundant object slot initialization, see #13341 (comment)

return {
pos: pos,
value: null,
type: type,
start: start,
end: end,
lastTokEnd: end,
// exprAllowed and inType is only used in readToken_slash
exprAllowed: exprAllowed,
inType: inType,
context: [this.curContext()],
};
} else {
// We observe inconsistent behavior in
// https://github.com/babel/babel/pull/13374
// which is likely a crankshaft bug, we don't expect it
// will be fixed since Node.js 6 reaches EOL.
// Before we drop Node 6 support, we have to clone
// the complete parser state
return state.clone();
}
}

/**
Expand All @@ -213,7 +225,7 @@ export default class Tokenizer extends ParserErrors {
*/
lookahead(): LookaheadState {
const old = this.state;
// For performance we use a simpified tokenizer state structure
// In Babel 8 we use a simpified tokenizer state structure
// $FlowIgnore
this.state = this.createLookaheadState(old);

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