Browser says "SyntaxError: '' is not a valid selector"

[honix]

Firefox 51.0.1 (64-bit) at Arch Linux

Browser console:
SyntaxError: '' is not a valid selector skewer:210
query http://127.0.0.1:8080/skewer:210:16
skewer.fn.html http://127.0.0.1:8080/skewer:218:18
callback http://127.0.0.1:8080/skewer:14:22
skewer.getJSON/xhr.onreadystatechange http://127.0.0.1:8080/skewer:39:13

[skeeto]

Can you provide the HTML that's causing this error and describe the operation you're attempting on it?

[terminalcommand]

Hello, same error happens to me on Firefox 56 on Lubuntu 17.10.

After I run M-x run-skewer and switch to skewer-repl, any command I type and send causes this error.

I've set up chromium as my browser and tried it again, it gives an error on the same line, but the error message is more explanatory.

Failed to load resource: the server responded with a status of 404 (Not Found)
skewer:212 Uncaught DOMException: Failed to execute 'querySelector' on 'Document': The provided selector is empty.
at query (http://127.0.0.1:8080/skewer:212:25)
at Object.skewer.fn.html (http://127.0.0.1:8080/skewer:220:18)
at callback (http://127.0.0.1:8080/skewer:14:45)
at XMLHttpRequest.xhr.onreadystatechange (http://127.0.0.1:8080/skewer:40:13)

The function that gives the error is:
function query(ancestry) { return document.querySelector(buildSelector(ancestry)); // this line is problematic }

buildSelector(ancestry) returns empty, and therefore document.querySelector(nil) fails.

I installed skewer directly from melpa.

I'd be happy to provide more information.

[Ruin0x11]

Happens to me also. Running the demo included with skewer fails with the same message. I used Chrome 65 on Windows 7.

Uncaught DOMException: Failed to execute 'querySelector' on 'Document': The provided selector is empty.
    at query (http://127.0.0.1:8080/skewer:212:25)
    at Object.skewer.fn.html (http://127.0.0.1:8080/skewer:220:18)
    at callback (http://127.0.0.1:8080/skewer:14:45)
    at XMLHttpRequest.xhr.onreadystatechange (http://127.0.0.1:8080/skewer:40:13)

It seems to try evaluating the top-level HTML tag on startup but fails because the ancestry list is null, which ends up creating a blank CSS selector. But the blank ancestry list is created in Emacs as well when I evaluate skewer-html-compute-tag-ancestry on the top level tag.

As a workaround I modified skewer-html-compute-tag-ancestry as follows:

(defun skewer-html-compute-tag-ancestry ()
  "Compute the ancestry chain at point."
  (skewer-html--with-html-mode
    (nreverse
     (cl-loop for tag in (skewer-html--get-context)
              for nth = (skewer-html-compute-tag-nth (1+ (sgml-tag-start tag)))
              for name = (skewer-html--cleanup tag)
              ;;unless (equal name "html")
              collect (list name nth)))))

This way an html tag will always be included in the ancestry. Then everything works swimmingly.

[vlnn]

So.. any progress on this? The problem is still there as far as I see. @skeeto do you think the solution provided by @Ruin0x11 is good enough to be merged?