Revert "Bug 23104: Add a default line height compensation"

Bug 40919: Drop line-height protection introduced in #23104. The main purpose of this patch was to hide the operating system. However, we don't hide it anymore, so it is not necessary and we do not have any proof of other benefits e.g., that it hides the OS minor version. This reverts commit 15172f28.

Revert "Bug 23104: Add a default line height compensation"
792ec04b · Pier Angelo Vendrame · 4e56f637 · 792ec04b · 792ec04b · 4e56f637
Verified Commit 792ec04b authored Apr 11, 2024 by Pier Angelo Vendrame
--- a/layout/generic/ReflowInput.cpp
+++ b/layout/generic/ReflowInput.cpp
@@ -34,7 +34,6 @@
 #include "nsTableCellFrame.h"
 #include "nsTableFrame.h"
 #include "StickyScrollContainer.h"
-#include "nsContentUtils.h"

 using namespace mozilla;
 using namespace mozilla::css;
@@ -2724,12 +2723,12 @@ void ReflowInput::CalculateBlockSideMargins() {
 // This is necessary because without this compensation, normal line height might
 // look too tight.
 constexpr float kNormalLineHeightFactor = 1.2f;
-static nscoord GetNormalLineHeight(nsFontMetrics* aFontMetrics, bool aRFP) {
+static nscoord GetNormalLineHeight(nsFontMetrics* aFontMetrics) {
  MOZ_ASSERT(aFontMetrics, "no font metrics");
  nscoord externalLeading = aFontMetrics->ExternalLeading();
  nscoord internalLeading = aFontMetrics->InternalLeading();
  nscoord emHeight = aFontMetrics->EmHeight();
-  if ((!internalLeading && !externalLeading) || aRFP) {
+  if (!internalLeading && !externalLeading) {
    return NSToCoordRound(emHeight * kNormalLineHeightFactor);
  }
  return emHeight + internalLeading + externalLeading;
@@ -2769,9 +2768,7 @@ static inline nscoord ComputeLineHeight(const StyleLineHeight& aLh,
    RefPtr<nsFontMetrics> fm = nsLayoutUtils::GetMetricsFor(
        aPresContext, aIsVertical, &aRelativeToFont, size,
        /* aUseUserFontSet = */ true);
-    return GetNormalLineHeight(
-        fm, aPresContext->Document()->ShouldResistFingerprinting(
-                RFPTarget::Unknown));
+    return GetNormalLineHeight(fm);
  }
  // If we don't have a pres context, use a 1.2em fallback.
  size.ScaleBy(kNormalLineHeightFactor);

--- a/layout/generic/test/mochitest.ini
+++ b/layout/generic/test/mochitest.ini
@@ -164,4 +164,3 @@ support-files =
 [test_scroll_on_display_contents.html]
 support-files = !/gfx/layers/apz/test/mochitest/apz_test_native_event_utils.js
 [test_bug1803209.html]
-[test_tor_bug23104.html]
--- a/layout/generic/test/test_tor_bug23104.html
+++ b/layout/generic/test/test_tor_bug23104.html
-<!DOCTYPE HTML>
-<meta charset="UTF-8">
-<html>
-<head>
-  <title>Test for Tor Bug #23104: CSS line-height reveals the platform Tor browser is running</title>
-  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
-  <script type="application/javascript" src="/tests/SimpleTest/SpawnTask.js"></script>
-  <style type="text/css">
-    span {
-      background-color: #000;
-      color: #fff;
-      font-size: 16.5px;
-    }
-  </style>
-</head>
-<body>
-<span id="test1">Test1</span>
-<span id="test2">كلمة</span>
-<span id="test3">ação</span>
-<script>
-
-let setPref = async function (key, value) {
-  await SpecialPowers.pushPrefEnv({"set": [[key, value]]});
-}
-
-function getStyle(el, styleprop) {
-  el = document.getElementById(el);
-  return document.defaultView.getComputedStyle(el, null).getPropertyValue(styleprop);
-}
-
-function validateElement(elementName, isFingerprintResistent) {
-  var fontSize = getStyle(elementName, 'font-size');
-  var lineHeight = getStyle(elementName, 'line-height');
-  var validationCb = isFingerprintResistent ? is : isnot;
-  validationCb(parseFloat(lineHeight), Math.round(parseFloat(fontSize)) * 1.2, 'Line Height validation');
-}
-
-add_task(async function() {
-  await setPref("layout.css.line-height.normal-as-resolved-value.enabled", false);
-  for (let resistFingerprintingValue of [true, false]) {
-    await setPref("privacy.resistFingerprinting", resistFingerprintingValue);
-    for (let elementId of ['test1', 'test2', 'test3']) {
-      validateElement(elementId, resistFingerprintingValue);
-    }
-  }
-});
-
-</script>
-</body>
-</html>