XPath syntax problems should make the query fail before execution

[smola]

Using double quotes here '//*[@role="Return"]' will make the XPath expression not valid:

gitbase_1      | time="2018-10-05T09:05:33Z" level=warning msg="unable to parse the given blob using bblfsh: rpc error: code = Unknown desc = check: key \"escapedValue\": invalid syntax (\"\\1\")"

It would be good to validate this during analysis and fail.

[kuba--]

I'm closing so far. Looks that the problem was during parsing a blob (missed escaped characters).
Bblfsh doesn't complain on any xpath.
If we encounter this kind of issue in the future we can reopen it.
Maybe as a future improvement we can add xpath validator to bblfsh client-go.v3

[bzz]

@kuba-- jfyi there already is an API for validating XPath in SDK

import github.com/bblfsh/sdk/uast/query/xpath

idx := xpath.New()
q, err := idx.Prepare("//uast:Identifier")
if err != nil {
  //handle it
}
q.Execute(uast)

And ofc upon feature request in a new issue it can be exposed in client-go.

[kuba--]

@bzz - we've already used a new stuff. Look at my comments: #635

The problem is the 3rd party library (https://github.com/antchfx/xpath/blob/master/xpath.go#L139).
The xpath.Compile (parse) function doesn't validate xpath string (only checks if it's empty/nil or not). For instance following tests passes:

func TestBblfsh(t *testing.T) {
    var err error
    var x *Expr

    x, err = Compile("//*[@role=\"Return\"]")
    if err != nil {
        t.Fatalf("should be correct but got error %s", err)
    }
    t.Logf("%v\n", x)

    x, err = Compile("BAD")
    if err != nil {
        t.Fatalf("should be correct but got error %s", err)
    }
    t.Logf("%v\n", x)

    x, err = Compile("this is a totally crap. For sure not valid @xpath")
    if err != nil {
        t.Fatalf("should be correct but got error %s", err)
    }
    t.Logf("%v\n", x)

    x, err = Compile("//*")
    if err != nil {
        t.Fatalf("should be correct but got error %s", err)
    }
    t.Logf("%v\n", x)

    /*
        x, err = Compile("")
        if err != nil {
            t.Fatalf("should be correct but got error %s", err)
        }
        t.Logf("%v\n", x)
    */
}