Avoid text selection workaround in modern Chromium

[nicolo-ribaudo]

Avoid text selection workaround in modern Chromium

Chromium 148+ improved their selection behavior when it comes to absolutely positioned elements, thus making text selectino in PDF.js much better.

Unfortunately this does not only mean that the workaround we currently have for Chromium is unnecessary, but it actually become harmful. It conflicts with Chromium's new behavior, making text selection worse on mobile.

As the change has been released in Chrome only a month ago, this patch keeps the workaround for older Chromium versions. There is no easy way to feture-detect is, so unfortunately we need to do user agent version detection.

Also, somehow the "right click on images" layer undoes the negative effects of the workaround, so even in modern mobile Chromium if there are images text selection already works well.

This is the behavior on various Chromium versions. By "scroll jump" I meant that the page scroll position moves to the wrong place (usually top right of the page) while selection; by "selection explodes" I mean that suddenly all the page is selected while trying to select something.

Chromium version	Input	Before this PR	After this PR
≥ 148	Touch	❌ Scroll jump	✔️
≥ 148	Mouse	✔️	✔️ (but running less code!)
< 148	Touch	❌ Scroll jump	❌ Scroll jump
< 148	Mouse	✔️	✔️

The changed code is not included in the mozcentral build. In the Chromium build it now looks like this:

      if (isFirefoxOrModernChromium === undefined) {
        const chromiumVersion = navigator.userAgentData ? navigator.userAgentData.brands.find(({
          brand
        }) => brand === "Chromium")?.version : /\bChrome\/(\d+)\b/.exec(navigator.userAgent)?.[1];
        isFirefoxOrModernChromium = !!chromiumVersion && parseInt(chromiumVersion, 10) >= 148;
      }
      if (isFirefoxOrModernChromium) {
        return;
      }

while in the generic build it looks like this:

      if (isFirefoxOrModernChromium === undefined) {
        isFirefoxOrModernChromium = getComputedStyle(this.#textLayers.values().next().value).getPropertyValue("-moz-user-select") === "none";
        if (!isFirefoxOrModernChromium) {
          const chromiumVersion = navigator.userAgentData ? navigator.userAgentData.brands.find(({
            brand
          }) => brand === "Chromium")?.version : /\bChrome\/(\d+)\b/.exec(navigator.userAgent)?.[1];
          isFirefoxOrModernChromium = !!chromiumVersion && parseInt(chromiumVersion, 10) >= 148;
        }
      }
      if (isFirefoxOrModernChromium) {
        return;
      }

[timvandermeij]

Looks good to me, with passing CI (GitHub Actions) and browser (bot) tests. It looks like the GitHub Actions builds somehow did not start; could you perhaps re-push the change to retrigger them?

Thank you for improving this, and for the detailed analysis in the PR body (as that really helps to understand the change)!

[timvandermeij]

/botio browsertest

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Received

Command cmd_browsertest from @timvandermeij received. Current queue size: 1

Live output at: http://54.241.84.105:8877/09d0b2d27676b7d/output.txt

[moz-tools-bot]

From: Bot.io (Windows)

---

Received

Command cmd_browsertest from @timvandermeij received. Current queue size: 1

Live output at: http://54.193.163.58:8877/71039d40cd4de38/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Success

Full output at http://54.241.84.105:8877/09d0b2d27676b7d/output.txt

Total script time: 18.13 mins

• Regression tests: Passed

[moz-tools-bot]

From: Bot.io (Windows)

---

Success

Full output at http://54.193.163.58:8877/71039d40cd4de38/output.txt

Total script time: 25.00 mins

• Regression tests: Passed

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.08%. Comparing base (04eeeec) to head (ea43bb4).
⚠️ Report is 39 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21514      +/-   ##
==========================================
- Coverage   89.79%   89.08%   -0.72%     
==========================================
  Files         260      262       +2     
  Lines       66282    67013     +731     
==========================================
+ Hits        59520    59698     +178     
- Misses       6762     7315     +553     

Flag	Coverage Δ
browsertest	66.51% <0.00%> (-0.18%)	⬇️
integrationtest	68.53% <100.00%> (-0.40%)	⬇️
unittest	57.29% <0.00%> (+0.04%)	⬆️
unittestcli	56.27% <0.00%> (+0.06%)	⬆️

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[nicolo-ribaudo]

I need to investigate the integration test failures, it's possible I just need to update the expected behavior

[nicolo-ribaudo]

Done :)