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fix: async arrow functions should not be allowed after binary operator. #11284

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merged 4 commits into from Mar 21, 2020
Merged

fix: async arrow functions should not be allowed after binary operator. #11284

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d2dfcc9
Forbid async arrow functions after binary operator.
vedantroy Mar 18, 2020
203b2f2
Make atPossibleAsync more accurate
vedantroy Mar 19, 2020
7e1efe2
Change atPossibleAsync to atPossibleAsyncArrow
vedantroy Mar 20, 2020
603a3cd
Add test for async arrow after unary operator
vedantroy Mar 21, 2020
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8 changes: 5 additions & 3 deletions packages/babel-parser/src/parser/expression.js
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Expand Up @@ -556,7 +556,7 @@ export default class ExpressionParser extends LValParser {
): N.Expression {
const state = {
optionalChainMember: false,
maybeAsyncArrow: this.atPossibleAsync(base),
maybeAsyncArrow: this.atPossibleAsyncArrow(base),
stop: false,
};
do {
Expand Down Expand Up @@ -748,13 +748,15 @@ export default class ExpressionParser extends LValParser {
return this.finishNode(node, "TaggedTemplateExpression");
}

atPossibleAsync(base: N.Expression): boolean {
atPossibleAsyncArrow(base: N.Expression): boolean {
return (
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The conditions here corresponds to atPossibleAsync. I was meant to add base.start === this.state.potentialArrowAt here so it can be rebranded as atPossibleAsyncArrow.

atPossibleAsyncArrow(base: N.Expression): boolean {
  return (base.type === "Identifier" &&
  base.name === "async" &&
  this.state.lastTokEnd === base.end &&
  !this.canInsertSemicolon() &&
  base.end - base.start === 5 &&
  base.start === this.state.potentialArrowAt)
}

The first 5 conditions are about atPossibleAsync and the last one is hasPossibleArrow so it combines into atPossibleAsyncArrow.

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I think I understand. I'll add the extra condition to this atPossibleAsyncArrow method, and delete the atPossibleAsync method. This means I will also change

if (!noCalls && this.atPossibleAsync(base)) {

in the Typescript plugin to

if (!noCalls && this.atPossibleAsyncArrow(base)) {

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If you are going with the base.end - base.start === 5 route, could you add a comment in the code that it's needed to check that there are no escape sequences?

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Half joking: If this.state.lastTokEnd >= base.end && base.start >= this.state.potentialArrowAt is always true (I don't know). We can even further simplify it to

return (base.type === "Identifier" &&
  base.name === "async" &&
  !this.canInsertSemicolon() &&
  this.state.lastTokEnd - this.state.potentialArrowAt === 5)
)

base.type === "Identifier" &&
base.name === "async" &&
this.state.lastTokEnd === base.end &&
!this.canInsertSemicolon() &&
this.input.slice(base.start, base.end) === "async"
// check there are no escape sequences, such as \u{61}sync
base.end - base.start === 5 &&
base.start === this.state.potentialArrowAt
);
}

Expand Down
2 changes: 1 addition & 1 deletion packages/babel-parser/src/plugins/typescript/index.js
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Expand Up @@ -1738,7 +1738,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
// There are number of things we are going to "maybe" parse, like type arguments on
// tagged template expressions. If any of them fail, walk it back and continue.
const result = this.tsTryParseAndCatch(() => {
if (!noCalls && this.atPossibleAsync(base)) {
if (!noCalls && this.atPossibleAsyncArrow(base)) {
// Almost certainly this is a generic async function `async <T>() => ...
// But it might be a call with a type argument `async<T>();`
const asyncArrowFn = this.tsTryParseGenericAsyncArrowFunction(
Expand Down
1 change: 1 addition & 0 deletions ...fixtures/es2016/simple-parameter-list/async-arrow-function-after-binary-operator/input.js
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@@ -0,0 +1 @@
3 + async() => 2
3 changes: 3 additions & 0 deletions ...ures/es2016/simple-parameter-list/async-arrow-function-after-binary-operator/options.json
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@@ -0,0 +1,3 @@
{
"throws": "Unexpected token, expected \";\" (1:12)"
}
1 change: 1 addition & 0 deletions .../fixtures/es2016/simple-parameter-list/async-arrow-function-after-unary-operator/input.js
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@@ -0,0 +1 @@
delete async () => 3;
3 changes: 3 additions & 0 deletions ...tures/es2016/simple-parameter-list/async-arrow-function-after-unary-operator/options.json
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@@ -0,0 +1,3 @@
{
"throws": "Unexpected token, expected \";\" (1:16)"
}
1 change: 1 addition & 0 deletions ...st/fixtures/typescript/arrow-function/async-arrow-function-after-binary-operator/input.ts
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@@ -0,0 +1 @@
4 + async<number>() => 2
5 changes: 5 additions & 0 deletions ...ixtures/typescript/arrow-function/async-arrow-function-after-binary-operator/options.json
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@@ -0,0 +1,5 @@
{
"sourceType": "module",
"plugins": ["typescript"],
"throws": "Unexpected token, expected \";\" (1:20)"
}