lighthouse
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GoogleChrome
Handle accessibility incomplete and violations simultaneously
FAQ
- [X] Yes, my issue is not about variability or throttling.
- ~~[ ] Yes, my issue is not about a specific accessibility audit (file with axe-core instead).~~
URL
https://accessibility-experiments-90d5b5.netlify.app/lighthouse-bypass-audit/index.html
What happened?
The bypass audit based on Axe’s bypass rule always shows as passing when it’s applicable, even when there are issues on the page that Axe itself detects.
Sample page: https://accessibility-experiments-90d5b5.netlify.app/lighthouse-bypass-audit/index.html
Lighthouse results for bypass on this page (JSON export)
"bypass": {
"id": "bypass",
"title": "The page contains a heading, skip link, or landmark region",
"description": "Adding ways to bypass repetitive content lets keyboard users navigate the page more efficiently. [Learn more](https://web.dev/bypass/).",
"score": 1,
"scoreDisplayMode": "binary",
"details": {
"type": "table",
"headings": [],
"items": []
}
},
Axe CLI results for the same page
Command:
axe -r bypass https://accessibility-experiments-90d5b5.netlify.app/lighthouse-bypass-audit/index.html --save bypass.json && cat bypass.json
Output:
[
{
"testEngine": {
"name": "axe-core",
"version": "4.3.5"
},
"testRunner": {
"name": "axe"
},
"testEnvironment": {
"userAgent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/104.0.5112.101 Safari/537.36",
"windowWidth": 800,
"windowHeight": 600,
"orientationAngle": 0,
"orientationType": "landscape-primary"
},
"timestamp": "2022-09-03T10:13:28.251Z",
"url": "https://accessibility-experiments-90d5b5.netlify.app/lighthouse-bypass-audit/index.html",
"toolOptions": {
"runOnly": {
"type": "rule",
"values": [
"bypass"
]
},
"reporter": "v1"
},
"inapplicable": [],
"passes": [],
"incomplete": [
{
"id": "bypass",
"impact": "serious",
"tags": [
"cat.keyboard",
"wcag2a",
"wcag241",
"section508",
"section508.22.o"
],
"description": "Ensures each page has at least one mechanism for a user to bypass navigation and jump straight to the content",
"help": "Page must have means to bypass repeated blocks",
"helpUrl": "https://dequeuniversity.com/rules/axe/4.3/bypass?application=webdriverjs",
"nodes": [
{
"any": [
{
"id": "internal-link-present",
"data": null,
"relatedNodes": [],
"impact": "serious",
"message": "No valid skip link found"
},
{
"id": "header-present",
"data": null,
"relatedNodes": [],
"impact": "serious",
"message": "Page does not have a heading"
},
{
"id": "landmark",
"data": null,
"relatedNodes": [],
"impact": "serious",
"message": "Page does not have a landmark region"
}
],
"all": [],
"none": [],
"impact": "serious",
"html": "<html lang=\"en\" class=\"deque-axe-is-ready\">",
"target": [
"html"
],
"failureSummary": "Fix any of the following:\n No valid skip link found\n Page does not have a heading\n Page does not have a landmark region"
}
]
}
],
"violations": []
}
]
What did you expect?
Lighthouse’s results for bypass should be consistent with those of Axe. In this instance, Axe reports bypass as "incomplete", so it shouldn’t be a pass with Lighthouse. I would have expected either a "Additional items to manually check", or an error.
What have you tried?
I’ve investigated how the Axe rule works, and suspect the issue is due to Axe changing the output of this rule from violations to incomplete. This apparently happened in Axe v4.2 because although the rule can detect the absence of "bypass" functionality, it can’t detect whether there is actually anything to bypass on a page.
I suspect the issue in Lighthouse is in the Axe audit processing logic, around here, where Axe handles incomplete results differently based on the audit’s display mode:
https://github.com/GoogleChrome/lighthouse/blob/fd304ed182bcbf66bb4225e474be9799f14667b1/core/audits/accessibility/axe-audit.js#L47-L58
I’m unclear whether the current logic could work or whether there needs to be additions here.
How were you running Lighthouse?
Chrome DevTools, web.dev
Lighthouse Version
9.6.6
Chrome Version
107
Node Version
No response
OS
Mac
Relevant log output
No response
Thanks for reporting this and doing an investigation! Not very often that someone reports a page that should be failing an audit but isn't.
Your analysis is correct. The failure is hidden by this line: https://github.com/GoogleChrome/lighthouse/blob/fd304ed182bcbf66bb4225e474be9799f14667b1/core/audits/accessibility/axe-audit.js#L58
The audit is not classified as informative so we ignore any incomplete reports from axe. I think it's worth discussing making the bypass audit informative to surface these cases.
- we could just make this audit informative
- or we could show incomplete items w/o it impacting the score of non-informative axe audits
ref:
https://github.com/GoogleChrome/lighthouse/pull/10056#discussion_r354563204 https://github.com/GoogleChrome/lighthouse/pull/10072 https://github.com/GoogleChrome/lighthouse/pull/12536#issuecomment-864454874
FYI I’ve opened #14438 and #14439, which are the same issue as this as far as I can tell, just with different audits. Feel free to close those if it’s better to handle all three problematic audits at once.
Those are the only three audits where I suspected this issue. I spotted this as part of the Accessibility chapter of the HTTP Archive’s Web Almanac, where we review Lighthouse audit scores across 8M websites. Those 3 audits are the only ones that run on hundreds of thousands / millions of pages, and didn’t report a single failure. Here is the Lighthouse audit data if anyone wants to spend more time looking, and our SQL query (BigQuery).
Thanks for the research @thibaudcolas! I think should merge everything into this audit, but good to know which audits this problem affects.
- [x] (10.0) make these audits informative
or (if possible for incomplete and violations to both occur)
- [ ] if only incomplete, mark
informative - [ ] if incomplete and violations, emit them as two separate tables
- [ ] if just violations, do what we do today
to rationalize the whole axe informative behavior, start with thread here: https://github.com/GoogleChrome/lighthouse/pull/12536#issuecomment-849740974
