Bug 1890523 - Remove extra space above/below stretchy operators. r=em…

…ilio

Gecko always adds .2em space above and below stretchy operators but this
is not part of MathML Core and is causing several WPT failures. The
MATH table does not have any parameter for that so it's likely some
tweak that was added in the early days of MathML that may no longer be
necessary. This patch tentatively removes this feature by placing it
under a disabled-by-default flag.

Differential Revision: https://phabricator.services.mozilla.com/D207014

layout/mathml/nsMathMLmoFrame.cpp

@@ -596,9 +596,15 @@ nsMathMLmoFrame::Stretch(DrawTarget* aDrawTarget,
 
   // get the leading to be left at the top and the bottom of the stretched char
   // this seems more reliable than using fm->GetLeading() on suspicious fonts
-  nscoord em;
-  GetEmHeight(fm, em);
-  nscoord leading = NSToCoordRound(0.2f * em);
+  const nscoord leading = [&fm] {
+    if (StaticPrefs::
+            mathml_top_bottom_spacing_for_stretchy_operators_disabled()) {
+      return 0;
+    }
+    nscoord em;
+    GetEmHeight(fm, em);
+    return NSToCoordRound(0.2f * (float)em);
+  }();
 
   // Operators that are stretchy, or those that are to be centered
   // to cater for fonts that are not math-aware, are handled by the MathMLChar

modules/libpref/init/StaticPrefList.yaml

@@ -9548,6 +9548,13 @@
   mirror: always
   rust: true
 
+# Whether to disable extra top/bottom spacing for stretchy operators.
+- name: mathml.top_bottom_spacing_for_stretchy_operators.disabled
+  type: bool
+  value: true
+  mirror: always
+  rust: true
+
 #---------------------------------------------------------------------------
 # Prefs starting with "media."
 #---------------------------------------------------------------------------

testing/web-platform/meta/mathml/presentation-markup/mrow/stretch-along-block-axis-001.html.ini

@@ -1,17 +1,6 @@
 [stretch-along-block-axis-001.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]
-  [Taking into account stretch axis.]
-    expected: FAIL
-
-  [Taking into account stretchy property.]
-    expected: FAIL
-
   [Only operators with a stretchy property and block stretch axis.]
     expected: FAIL
 
   [Operators smaller and larger than non-stretchy siblings.]
     expected: FAIL
-
-  [Embellished operators]
-    expected: FAIL

testing/web-platform/meta/mathml/presentation-markup/operators/mo-minsize-maxsize-001.html.ini

@@ -1,20 +1,6 @@
 [mo-minsize-maxsize-001.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]
   [minsize < maxsize < 0 is treated as maxsize = minsize = 0]
     expected: FAIL
 
-  [minsize < 0 is treated as 0]
-    expected: FAIL
-
-  [target size = 0 is treated as Tascent = Tdescent = minsize/2]
-    expected: FAIL
-
-  [maxsize < minsize is treated as maxsize = minsize]
-    expected: FAIL
-
   [minsize/maxsize percentages are relative to the target size]
     expected: FAIL
-
-  [default minsize/maxsize percentages]
-    expected: FAIL