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Parse error is confusing when trying to return two elements #1584

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sophiebits opened this issue May 21, 2014 · 1 comment · Fixed by facebookarchive/esprima#20
Closed

Parse error is confusing when trying to return two elements #1584

sophiebits opened this issue May 21, 2014 · 1 comment · Fixed by facebookarchive/esprima#20

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@sophiebits
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(Opening here because esprima-fb apparently doesn't accept issues.)

If you write

return <div className="one" /><div className="two" />;

then you get "Unexpected identifier" because it tries to parse it as

return React.DOM.div({className: "one"})  < div className ...

That is, the < of the second div is interpreted as a less than. I think we can give nicer errors here if we disallow the less than operator directly after an XJSElement. I don't think this prevents any real uses but if it did, you could always wrap it in parens:

return (<div className="one" />) < threshold;

cc @jeffmo @syranide
sophiebits added a commit to sophiebits/esprima that referenced this issue May 22, 2014
@sophiebits
Add friendlier error for two adjacent elements
2707d2e 
Fixes facebook/react#1584.

Test Plan: npm test
@sophiebits sophiebits mentioned this issue May 22, 2014
Merged
sophiebits added a commit to sophiebits/esprima that referenced this issue May 22, 2014
@sophiebits
Add friendlier error for two adjacent elements
b8d86f3 
Fixes facebook/react#1584.

Test Plan: npm test
@sophiebits
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facebookarchive/esprima#20 was merged; we can close this after a version bump.

josephsavona added a commit that referenced this issue May 15, 2024
@josephsavona
Implement dominator/post-dominator tree calculation
2ddd00d 
Implements an efficient algorithm for computing the dominator (or post 
dominator) tree of a CFG, following 
https://www.cs.rice.edu/~keith/Embed/dom.pdf. This is used/tested in the next PR 
to validate that hooks are called unconditionally. 

note: I clean up the implementation quite a bit late in the stack in #1584
josephsavona added a commit that referenced this issue May 15, 2024
@josephsavona
Dont count throw as an exit node (React semantics)
8920fc0 
React will retry or abort components that throw (depending on a few conditions), 
so from React's perspective a `throw` statement is not a normal exit node. Thus 
the Rules of Hooks really have a caveat: the set of hooks that are called _in an 
execution that returns successfully_ must be consistent. Examples such as the 
following are therefore allowed: 

```javascript 

function Component(props) { 

if (props.cond) { 

throw new Error(...); 

} 

useHook(); 

} 

``` 

By modeling `throw` as an exit node, we rejected cases such as this. This diff 
changes to not model throws as exit nodes. #1584  changes this to make it an 
option, since some cases will want to consider throw as an exit node.
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Add friendlier error for two adjacent elements sophiebits/esprima
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@sophiebits