Validate XPath query before use it with the new bblfsh api

[ajnavarro]

More info here: https://github.com/bblfsh/sdk/blob/4ba719e80ab52f2d4da5ac8a6f4675687c6fe952/uast/query/xpath/xpath.go#L22

[kuba--]

@ajnavarro, @bzz
I think we already uses the new stuff!

In function func (u *uastFunc) getUAST we call nodeArray, err = applyXpath(node, xpath) (https://github.com/src-d/gitbase/blob/master/internal/function/uast.go#L250)

applyXpath calls it, err := tools.Filter(n, query) (where tools.Filter is gopkg.in/bblfsh/client-go.v3/tools/context.go#L116)
It creates a new context with xpath: xpath.New(), and calls xpath.Execute:

if query == "" {
		query = "//*"
}
return c.xpath.Execute(c.root, query)

where c.xpath.Execute is exactly the function:
https://github.com/src-d/gitbase/blob/master/vendor/gopkg.in/bblfsh/sdk.v2/uast/query/xpath/xpath.go#L30

So every time when we apply xpath via tools wrapper we compile and execute xpath.

[ajnavarro]

@kuba-- but we are not failing the query if the xpath is wrong, maybe we should fail on that case.

[kuba--]

It should be fixed by 3rd party package: https://github.com/antchfx/xpath/blob/master/xpath.go#L139

[ajnavarro]

Related: bblfsh/sdk#332

[kuba--]

If we switch to the gopkg.in/xmlpath.v2at least in following test it can find the last invalid xpath (github.com/antchfx/xpath is the lib. which bblfsh uses right now):

package main

import (
	. "gopkg.in/xmlpath.v2"
	// . "github.com/antchfx/xpath"
)
func main() {
	MustCompile("//*[@role=\"Return\"]")
	MustCompile("BAD")

	MustCompile("this is a totally crap. For sure not valid @xpath") // <----
}

[erizocosmico]

What shall we do with this? @ajnavarro

[ajnavarro]

we can close this as cannot be fixed from our side.