Bug 1741469 part 3: Add an off-by-default pref to control whether input type="number"/"range" fields are modified when mousewheel-scrolled. r=smaug

The C++ code change here is simply replacing an ifdef with a pref-check (and
associated reindentation for being placed in an "if"-block).

The pref is off-by-default for now, since no other browser seems to modify
these fields through mousewheel scrolling, and users seem to be surprised when
they encounter the behavior in Firefox.  See discussion on the bugzilla page.

Note: now that this behavior is controlled by a pref, we don't need to have
platform-specific #ifdefs and "skip-if" test exemptions. If we decide to bring
this behavior back on certain platforms, we can do so by simply changing the
default value of the pref on those platforms.

Differential Revision: https://phabricator.services.mozilla.com/D175719

dom/html/HTMLInputElement.cpp

@@ -3962,39 +3962,42 @@ nsresult HTMLInputElement::PostHandleEvent(EventChainPostVisitor& aVisitor) {
           }
           break;
         }
-#if !defined(ANDROID) && !defined(XP_MACOSX)
         case eWheel: {
-          // Handle wheel events as increasing / decreasing the input element's
-          // value when it's focused and it's type is number or range.
-          WidgetWheelEvent* wheelEvent = aVisitor.mEvent->AsWheelEvent();
-          if (!aVisitor.mEvent->DefaultPrevented() &&
-              aVisitor.mEvent->IsTrusted() && IsMutable() && wheelEvent &&
-              wheelEvent->mDeltaY != 0 &&
-              wheelEvent->mDeltaMode != WheelEvent_Binding::DOM_DELTA_PIXEL) {
-            if (mType == FormControlType::InputNumber) {
-              if (nsContentUtils::IsFocusedContent(this)) {
-                StepNumberControlForUserEvent(wheelEvent->mDeltaY > 0 ? -1 : 1);
+          if (StaticPrefs::
+                  dom_input_number_and_range_modified_by_mousewheel()) {
+            // Handle wheel events as increasing / decreasing the input
+            // element's value when it's focused and it's type is number or
+            // range.
+            WidgetWheelEvent* wheelEvent = aVisitor.mEvent->AsWheelEvent();
+            if (!aVisitor.mEvent->DefaultPrevented() &&
+                aVisitor.mEvent->IsTrusted() && IsMutable() && wheelEvent &&
+                wheelEvent->mDeltaY != 0 &&
+                wheelEvent->mDeltaMode != WheelEvent_Binding::DOM_DELTA_PIXEL) {
+              if (mType == FormControlType::InputNumber) {
+                if (nsContentUtils::IsFocusedContent(this)) {
+                  StepNumberControlForUserEvent(wheelEvent->mDeltaY > 0 ? -1
+                                                                        : 1);
+                  FireChangeEventIfNeeded();
+                  aVisitor.mEvent->PreventDefault();
+                }
+              } else if (mType == FormControlType::InputRange &&
+                         nsContentUtils::IsFocusedContent(this) &&
+                         GetMinimum() < GetMaximum()) {
+                Decimal value = GetValueAsDecimal();
+                Decimal step = GetStep();
+                if (step == kStepAny) {
+                  step = GetDefaultStep();
+                }
+                MOZ_ASSERT(value.isFinite() && step.isFinite());
+                SetValueOfRangeForUserEvent(
+                    wheelEvent->mDeltaY < 0 ? value + step : value - step);
                 FireChangeEventIfNeeded();
                 aVisitor.mEvent->PreventDefault();
               }
-            } else if (mType == FormControlType::InputRange &&
-                       nsContentUtils::IsFocusedContent(this) &&
-                       GetMinimum() < GetMaximum()) {
-              Decimal value = GetValueAsDecimal();
-              Decimal step = GetStep();
-              if (step == kStepAny) {
-                step = GetDefaultStep();
-              }
-              MOZ_ASSERT(value.isFinite() && step.isFinite());
-              SetValueOfRangeForUserEvent(
-                  wheelEvent->mDeltaY < 0 ? value + step : value - step);
-              FireChangeEventIfNeeded();
-              aVisitor.mEvent->PreventDefault();
             }
           }
           break;
         }
-#endif
         case ePointerClick: {
           if (!aVisitor.mEvent->DefaultPrevented() &&
               aVisitor.mEvent->IsTrusted() &&

dom/html/test/mochitest.toml

@@ -773,24 +773,10 @@ skip-if = [
 ]
 
 ["test_bug1261673.html"]
-skip-if = [
-  "os == 'android'",
-  "apple_catalina",
-  "apple_silicon",
-]
 
 ["test_bug1261674-1.html"]
-skip-if = [
-  "os == 'android'",
-  "apple_catalina",
-  "apple_silicon",
-]
 
 ["test_bug1261674-2.html"]
-skip-if = [
-  "apple_catalina",
-  "apple_silicon",
-]
 
 ["test_bug1264157.html"]
 

dom/html/test/test_bug1261673.html

@@ -52,6 +52,10 @@ function runTests() {
   let actualChangeCount = 0;
   let expectedChangeCount = 0;
 
+  const prefName = "dom.input.number_and_range_modified_by_mousewheel";
+  let didFlipPref = false;
+  let isPrefEnabled = SpecialPowers.getBoolPref(prefName);
+  is(isPrefEnabled, false,  "Expecting pref to be disabled by default");
   input.addEventListener("change", () => {
     ++actualChangeCount;
   });
@@ -59,22 +63,35 @@ function runTests() {
   function runNext() {
     let p = params[testIdx];
     (p.focus) ? input.focus() : input.blur();
-    if (p.valueChanged != 0) {
+    if (isPrefEnabled && p.valueChanged != 0) {
       expectedChangeCount++;
       expectedValue += p.valueChanged;
     }
 
     sendWheelAndPaint(input, 1, 1, { deltaY: p.deltaY, deltaMode: p.deltaMode },
-                      () => {
+                      async () => {
       is(parseInt(input.value), expectedValue,
-         "Handle wheel in number input test-" + testIdx);
+         "Handle wheel in number input test-" + testIdx +
+         " with pref " + (isPrefEnabled ? "en" : "dis") + "abled");
+
       is(actualChangeCount, expectedChangeCount,
          "UA should fire change event when input's value changed");
       if (++testIdx < params.length) {
         // More subtests remain; kick off the next one.
         runNext();
+      } else if (!didFlipPref) {
+        // Reached the end of the subtest list.  Flip the pref
+        // and restart our iteration over the subtests.
+        await SpecialPowers.pushPrefEnv({
+          set: [[prefName, !isPrefEnabled]],
+        });
+        isPrefEnabled = !isPrefEnabled;
+        didFlipPref = true;
+        testIdx = actualChangeCount = expectedChangeCount = 0;
+        runNext();
       } else {
-        // Reached the end of the subtest list. We're done!
+        // Reached the end of the subtest list, for both pref settings.
+        // We're done!
         SimpleTest.finish();
       }
     });

dom/html/test/test_bug1261674-1.html

@@ -52,6 +52,10 @@ function runTests() {
   let actualChangeCount = 0;
   let expectedChangeCount = 0;
 
+  const prefName = "dom.input.number_and_range_modified_by_mousewheel";
+  let didFlipPref = false;
+  let isPrefEnabled = SpecialPowers.getBoolPref(prefName);
+  is(isPrefEnabled, false,  "Expecting pref to be disabled by default");
   input.addEventListener("change", () => {
     ++actualChangeCount;
   });
@@ -59,22 +63,35 @@ function runTests() {
   function runNext() {
     let p = params[testIdx];
     (p.focus) ? input.focus() : input.blur();
-    if (p.valueChanged != 0) {
+    if (isPrefEnabled && p.valueChanged != 0) {
       expectedChangeCount++;
       expectedValue += p.valueChanged;
     }
 
     sendWheelAndPaint(input, 1, 1, { deltaY: p.deltaY, deltaMode: p.deltaMode },
-                      () => {
+                      async () => {
       is(parseInt(input.value), expectedValue,
-         "Handle wheel in range input test-" + testIdx);
+         "Handle wheel in range input test-" + testIdx +
+         " with pref " + (isPrefEnabled ? "en" : "dis") + "abled");
+
       is(actualChangeCount, expectedChangeCount,
          "UA should fire change event when input's value changed");
       if (++testIdx < params.length) {
         // More subtests remain; kick off the next one.
         runNext();
+      } else if (!didFlipPref) {
+        // Reached the end of the subtest list.  Flip the pref
+        // and restart our iteration over the subtests.
+        await SpecialPowers.pushPrefEnv({
+          set: [[prefName, !isPrefEnabled]],
+        });
+        isPrefEnabled = !isPrefEnabled;
+        didFlipPref = true;
+        testIdx = actualChangeCount = expectedChangeCount = 0;
+        runNext();
       } else {
-        // Reached the end of the subtest list. We're done!
+        // Reached the end of the subtest list, for both pref settings.
+        // We're done!
         SimpleTest.finish();
       }
     });

modules/libpref/init/StaticPrefList.yaml

@@ -3056,6 +3056,14 @@
   value: @IS_EARLY_BETA_OR_EARLIER@
   mirror: always
 
+# Does mousewheel-scrolling over a focused <input type="number"> or
+# <input type="range"> field cause the value to increase/decrease (rather
+# than scrolling the page)?
+- name: dom.input.number_and_range_modified_by_mousewheel
+  type: RelaxedAtomicBool
+  value: false
+  mirror: always
+
 # Whether to allow or disallow web apps to cancel `beforeinput` events caused
 # by MozEditableElement#setUserInput() which is used by autocomplete, autofill
 # and password manager.