Handle incorrect destructuring in for loops at parse time #2190
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added 2 commits
December 2, 2025 16:44
Code like this:
```js
for (var {};;) {}
```
was parsed correctly, but then failed during the code generation
with various exceptions because the destructuring expression after
`var` doesn't have a right-hand side.
This change implements a check at parse time, to throw a `SyntaxError`,
coherently with what `node` or `spidermonkey` or `quickjs` do.
I'm a bit surprised that this doesn't seem to show any improvement in
test262 coverage. Perhaps a test there might be warranted?
Fixes mozilla#1922
aardvark179
reviewed
Dec 2, 2025
Contributor
|
Ah, scratch that, it's a problem with a |
Contributor
Author
From what I can tell, this problem should only happen in |
Contributor
|
Okay looking at the spec and MDN I agree that the only places that allow destructuring binding are loops, functions, and catch blocks. |
aardvark179
approved these changes
Dec 5, 2025
rbri
reviewed
Dec 6, 2025
| public void errorOnInvalidDestructuringDeclaration() { | ||
| expectParseErrors( | ||
| "for(var {};;) {}", | ||
| new String[] {"Missing = in destructuring declaration", "syntax error"}); |
Collaborator
There was a problem hiding this comment.
As a reader of error messages i like this form more - not sure why the french version has the ' and the english not.
Missing '=' in destructuring declaration
rbri
approved these changes
Dec 6, 2025
Collaborator
|
Great, thanks! |
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Code like this:
was parsed correctly, but then failed during the code generation with various exceptions because the destructuring expression after
vardoesn't have a right-hand side.This change implements a check at parse time, to throw a
SyntaxError, coherently with whatnodeorspidermonkeyorquickjsdo.I'm a bit surprised that this doesn't seem to show any improvement in test262 coverage. Perhaps a test there might be warranted?
Fixes #1922