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Avoid unnecessary work during lookahead #9982

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merged 3 commits into from May 16, 2019
Merged

Avoid unnecessary work during lookahead #9982

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c3948f5
Do not call pushComment when doing lookahead
danez May 15, 2019
971df7e
Do no updateContext when doing lookahead
danez May 15, 2019
287e709
Do not clone contexts anymore
danez May 15, 2019
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18 changes: 12 additions & 6 deletions packages/babel-parser/src/tokenizer/index.js
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Expand Up @@ -226,11 +226,9 @@ export default class Tokenizer extends LocationParser {
loc: new SourceLocation(startLoc, endLoc),
};

if (!this.isLookahead) {
if (this.options.tokens) this.state.tokens.push(comment);
this.state.comments.push(comment);
this.addComment(comment);
}
if (this.options.tokens) this.state.tokens.push(comment);
this.state.comments.push(comment);
this.addComment(comment);
}

skipBlockComment(): void {
Expand All @@ -250,6 +248,10 @@ export default class Tokenizer extends LocationParser {
this.state.lineStart = match.index + match[0].length;
}

// If we are doing a lookahead right now we need to advance the position (above code)
// but we do not want to push the comment to the state.
if (this.isLookahead) return;

this.pushComment(
true,
this.input.slice(start + 2, end),
Expand All @@ -276,6 +278,10 @@ export default class Tokenizer extends LocationParser {
}
}

// If we are doing a lookahead right now we need to advance the position (above code)
// but we do not want to push the comment to the state.
if (this.isLookahead) return;

this.pushComment(
false,
this.input.slice(start + startSkip, this.state.pos),
Expand Down Expand Up @@ -350,7 +356,7 @@ export default class Tokenizer extends LocationParser {
this.state.type = type;
this.state.value = val;

this.updateContext(prevType);
if (!this.isLookahead) this.updateContext(prevType);
}

// ### Token reading
Expand Down
2 changes: 1 addition & 1 deletion packages/babel-parser/src/tokenizer/state.js
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Expand Up @@ -170,7 +170,7 @@ export default class State {
// $FlowIgnore
let val = this[key];

if ((!skipArrays || key === "context") && Array.isArray(val)) {
if (!skipArrays && Array.isArray(val)) {
val = val.slice();
}

Expand Down