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core(page-functions): don't try to clone a ShadowRoot #9079

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merged 9 commits into from
Jun 7, 2019
Merged

core(page-functions): don't try to clone a ShadowRoot #9079

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a5f9343
#9048 Fix Avoid an excess DOM size error
NickolasBenakis May 29, 2019
5de9be9
bug-fix: Avoid an excess DOM size error #9079
NickolasBenakis May 29, 2019
bf80f17
bug-fix: Avoid an excess DOM size error #9079
NickolasBenakis May 29, 2019
f34fd58
updates
patrickhulce May 31, 2019
51449a0
fix tests I broke
patrickhulce May 31, 2019
a1528b6
Add test for nodes that cannot be inspected
NickolasBenakis Jun 1, 2019
13d4753
Update lighthouse-core/lib/page-functions.js
NickolasBenakis Jun 4, 2019
29b209d
Update lighthouse-core/test/lib/page-functions-test.js
NickolasBenakis Jun 4, 2019
cbd0e48
ShadowRoot
brendankenny Jun 7, 2019
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12 changes: 12 additions & 0 deletions lighthouse-cli/test/fixtures/dobetterweb/dbw_tester.html
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Original file line number Diff line number Diff line change
Expand Up @@ -117,6 +117,18 @@
<object id="5934a"></object>
<object id="5934b"></object>

<div id="shadow-root-container"></div>
<script>
// DOM Size has had trouble with very specific shadow root traversal issues.
// Make sure it can handle reporting of the widest element being a shadow root.
const shadowRootContainer = document.getElementById('shadow-root-container');
const shadowRoot = shadowRootContainer.attachShadow({mode: 'open'});
for (let i = 0; i < 100; i++) {
const span = document.createElement('span');
shadowRoot.appendChild(span);
}
</script>

<script>
// Ensure gatherers still work when individual elements override '.matches'
document.getElementById("5934a").matches = "blahblah";
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10 changes: 7 additions & 3 deletions lighthouse-cli/test/smokehouse/dobetterweb/dbw-expectations.js
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Original file line number Diff line number Diff line change
Expand Up @@ -155,12 +155,16 @@ module.exports = [
},
'dom-size': {
score: 1,
numericValue: 35,
numericValue: 137,
details: {
items: [
{statistic: 'Total DOM Elements', value: '35'},
{statistic: 'Total DOM Elements', value: '137'},
{statistic: 'Maximum DOM Depth', value: '3'},
{statistic: 'Maximum Child Elements', value: '33'},
{
statistic: 'Maximum Child Elements',
value: '100',
element: {value: '<div id="shadow-root-container">'},
},
],
},
},
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26 changes: 16 additions & 10 deletions lighthouse-core/lib/page-functions.js
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@
// @ts-nocheck
'use strict';

/* global window document Node */
/* global window document Node ShadowRoot */

/**
* Helper functions that are passed by `toString()` by Driver to be evaluated in target page.
Expand Down Expand Up @@ -113,18 +113,24 @@ function getElementsInDocument(selector) {
*/
/* istanbul ignore next */
function getOuterHTMLSnippet(element, ignoreAttrs = []) {
const clone = element.cloneNode();

ignoreAttrs.forEach(attribute =>{
clone.removeAttribute(attribute);
});

const reOpeningTag = /^[\s\S]*?>/;
const match = clone.outerHTML.match(reOpeningTag);
try {
if (ShadowRoot.prototype.isPrototypeOf(element) && element.host && element.localName !== 'a') {
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nit:

Suggested change
if (ShadowRoot.prototype.isPrototypeOf(element) && element.host && element.localName !== 'a') {
if (element instanceof ShadowRoot && element.host && element.localName !== 'a') {

reads a little simpler than the prototype check, but

non-nit: can we also add a comment to this line? Both to explain the shadow root case, but also to explain the localName check. I don't really understand it...ShadowRoot doesn't have a localName, so by that point in the conditional won't the comparison always be true?

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(also according to spec "Shadow roots’s associated host is never null.")

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@patrickhulce since you added this line, what's the deal with the element.localName !== 'a' check?

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@patrickhulce patrickhulce Jun 5, 2019 •
edited
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This entire piece is straight up copied from the dom-size audit that filters this way, so you'd have to ask Eric as to why it was written this way :)

It indeed seemed like overkill and I thought about trying to extract this to a isShadowRoot function with a canonical version to do this or something but bringing in all the baggage of page-functions with dependencies into this PR seemed unfair.

I don't see why we can't just use element instanceof ShadowRoot personally, but I assumed Eric thought of something I didn't which is a pretty safe bet when it comes to our comparative web component/shadow dom knowledge 😆

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:P I commited the suggested changes,
is there any other issue that we need to tackle?

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This entire piece is straight up copied from the dom-size audit that filters this way, so you'd have to ask Eric as to why it was written this way :)

OK! After consulting the old texts (#2131), I think this was from adapting earlier code (which identified shadow roots just by looking for an element.host but had to rule out anchors because they also have a host property). That code was wrapped without modification in the ShadowRoot.prototype check in that PR, which I believe was the error (but since it's always true, it doesn't cause any bad behavior).

I'm going to remove based on the spec and my own testing saying it's fine. I'll take responsibility for any failures :)

element = element.host;
}

return (match && match[0]) || '';
const clone = element.cloneNode();
ignoreAttrs.forEach(attribute =>{
clone.removeAttribute(attribute);
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the types on this whole function get kind of broken if we aren't really accepting just Element.

removeAttribute and outerHTML (and more or less localName) exist only on Element.

Maybe we should type it as @param {Element|ShadowRoot} element and (if we don't need that localName check) have the conditional be just if (element instanceof ShadowRoot) element = element.host; (with a comment somewhere explaining that this function handles the ShadowRoot case).

It's still playing a little fast and loose with types (it doesn't help that the tsc built in types don't recognize ShadowRoot as a global value), but it simplifies things a bit.

});
const reOpeningTag = /^[\s\S]*?>/;
const match = clone.outerHTML.match(reOpeningTag);
return (match && match[0]) || '';
} catch (_) {
return `<${element.localName}>`;
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@connorjclark connorjclark Jun 3, 2019 •
edited
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can this entire range fail? if it's just the clone, could you reduce the try/catch to just that part?

a comment in the catch block would be useful.

}
}


/**
* Computes a memory/CPU performance benchmark index to determine rough device class.
* @see https://docs.google.com/spreadsheets/d/1E0gZwKsxegudkjJl8Fki_sOwHKpqgXwt8aBAfuUaB8A/edit?usp=sharing
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14 changes: 13 additions & 1 deletion lighthouse-core/test/lib/page-functions-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -16,10 +16,15 @@ describe('Page Functions', () => {
let dom;

beforeAll(() => {
const {document} = new jsdom.JSDOM().window;
const {document, ShadowRoot} = new jsdom.JSDOM().window;
global.ShadowRoot = ShadowRoot;
dom = new DOM(document);
});

afterAll(() => {
global.ShadowRoot = undefined;
});

describe('get outer HTML snippets', () => {
it('gets full HTML snippet', () => {
assert.equal(pageFunctions.getOuterHTMLSnippet(
Expand All @@ -38,6 +43,13 @@ describe('Page Functions', () => {
), '<div id="1">');
});

it('should handle dom nodes that cannot be inspected', () => {
const element = dom.createElement('div');
element.cloneNode = () => {
throw new Error('oops!');
};
assert.equal(pageFunctions.getOuterHTMLSnippet(element), '<div>');
});
it('ignores when attribute not found', () => {
assert.equal(pageFunctions.getOuterHTMLSnippet(
dom.createElement('div', '', {'id': '1', 'style': 'style', 'aria-label': 'label'}),
Expand Down