Raise error when invalid if-else chain is given

[estools]

Raise error when invalid if-else chain is given

[michaelficarra]

Nice catch. So the AST is too permissive. Maybe @dherman would be interested in modifying the mozilla parser API so that this impossible construct cannot be represented.

[Constellation]

Thanks.

#36 is related issue.
I think creating another project, something like esverify to verify AST is valid form (check node stat and types) and escodegen assumes that given AST is valid is good.
What do you think about this?

[michaelficarra]

Yes, #36 is related. I'm not sure about the esverify project, as that would make the input format for escodegen a moving target. It'd be ideal if we could structure the parser API in such a way that it allows nothing but valid constructs. Unfortunately, I don't think Mozilla will be too flexible there.

I'd be interested in what @dherman thinks.

[Constellation]

I'm not sure about the esverify project

Oops, sorry for misleading. This is an example of new project name, not existing project.

I'd be interested in what @dherman thinks.

Yes, me too.

[michaelficarra]

Oops, sorry for misleading.

No, no. I think there was a miscommunication. What I'm not sure about is whether it is a good idea.

Also, @ariya may want to be involved in this.

[Constellation]

miscommunication.

Oops, I misunderstood.

[ariya]

I'm fine either way. If the AST format permits something non-sensible, the consuming tool should understand that case. IMO it's not worth the effort to produce a format which is guaranteed to be associated with a valid syntax.

[michaelficarra]

Similarly, a TryStatement with an empty handlers list and a null finalizer property is a valid parser API construct, yet cannot be represented in JS syntax.

[michaelficarra]

Same goes for a BlockStatement whose first statement is an ExpressionStatement whose expression is a Literal whose value is a string. These will be parsed as DirectiveStatements, not strings.

[michaelficarra]

Also, to guarantee that parse(generate(tree)) == tree, we need to check that only valid operators are allowed in BinaryExpressions and LogicalExpressions.