Bug 12632 – XPath: Cannot apply predicate to context node.

• Component: XML
• Status: RESOLVED INVALID

[L. Daniel Burr]

The following expression, which works correctly in Opera and Firefox, throws "INVALID_EXPRESSION_ERR: DOM XPath Exception 51":

.[@*[]

This is just a simple example, but basically any attempt to apply a predicate to the context node fails with this error.  As noted above, Firefox and Opera both return the context node if the predicate evaluates as true.

[L. Daniel Burr]

Created attachment 12973 [details]
Small example for reproducing this bug.

[L. Daniel Burr]

(In reply to comment #0)
> The following expression, which works correctly in Opera and Firefox, throws
> "INVALID_EXPRESSION_ERR: DOM XPath Exception 51":
> 
> .[@*[]
>

Argh, somehow that didn't paste correctly.  It should be ".[@name='test']".  Note that the attached sample is correct, and will reproduce the problem accurately.
 
> This is just a simple example, but basically any attempt to apply a predicate
> to the context node fails with this error.  As noted above, Firefox and Opera
> both return the context node if the predicate evaluates as true.
> 

[Alexey Proskuryakov]

A workaround is to use full XPath syntax: "self::*[@class='test']".

[Alexey Proskuryakov]

Better yet, "self::node()[@class='test']"

[Alexey Proskuryakov]

I think WebKit is correct here, this syntax is invalid in XPath 1.0. See rule 4 - an abbreviated step cannot have predicates.

[4] Step ::= AxisSpecifier NodeTest Predicate*	
             | AbbreviatedStep

Also, see rule 20 - since "." is not a PrimaryExpr, it cannot start a FilterExpr either.

[20] FilterExpr ::= PrimaryExpr
                    | FilterExpr Predicate

From rule 20 comes another workaround: "(.)[@class='test']".

[Alexey Proskuryakov]

https://bugzilla.mozilla.org/show_bug.cgi?id=369522

[Alexey Proskuryakov]

*** Bug 17410 has been marked as a duplicate of this bug. ***

[Ahmad Saleem]

I am getting following behavior across all browsers:

*** Safari 15.6 on macOS 12.5 ***

Console errors when clicking link in attached test case - The string did not match the expected pattern.

*** Chrome Canary 106 ****

Console errors when clicking link in attached test case - The string '.[@class='test']' is not a valid XPath expression.

*** Firefox Nightly 104 ***

Nothing happens and there is no Console error.

_______

Comment 05 mentions that Webkit is right here, plus Firefox still has the bug open (Comment 06 was duplicate for https://bugzilla.mozilla.org/show_bug.cgi?id=164822). I think this can be considered as "RESOLVED INVALID" or "RESOLVED WONTFIX"? Thanks!