Bug 1099557 followup - Put the default setting for control-character visibility behind a runtime pref, and keep it off-by-default on release builds for now. r=dbaron

layout/reftests/text/reftest.list

@@ -316,10 +316,10 @@ pref(layout.css.text-align-true-value.enabled,true) == text-align-true.html text
 != control-chars-02.html control-chars-02-notref.html
 == control-chars-03a.html control-chars-03-ref.html
 == control-chars-03b.html control-chars-03-ref.html
-!= control-chars-04a.html control-chars-04-notref.html
-!= control-chars-04b.html control-chars-04-notref.html
-!= control-chars-04c.html control-chars-04-notref.html
-!= control-chars-04d.html control-chars-04-notref.html
+pref(layout.css.control-characters.visible,true) != control-chars-04a.html control-chars-04-notref.html
+pref(layout.css.control-characters.visible,true) != control-chars-04b.html control-chars-04-notref.html
+pref(layout.css.control-characters.visible,true) != control-chars-04c.html control-chars-04-notref.html
+pref(layout.css.control-characters.visible,true) != control-chars-04d.html control-chars-04-notref.html
 
 # font fallback for <space> when not supported in the primary font family - bug 970891
 HTTP(..) == space-font-1.html space-font-1-ref.html

layout/style/nsCSSParser.cpp

@@ -62,6 +62,7 @@ static bool sUnprefixingServiceEnabled;
 static bool sUnprefixingServiceGloballyWhitelisted;
 #endif
 static bool sMozGradientsEnabled;
+static bool sControlCharVisibility;
 
 const uint32_t
 nsCSSProps::kParserVariantTable[eCSSProperty_COUNT_no_shorthands] = {
@@ -15717,6 +15718,8 @@ nsCSSParser::Startup()
 #endif
   Preferences::AddBoolVarCache(&sMozGradientsEnabled,
                                "layout.css.prefixes.gradients");
+  Preferences::AddBoolVarCache(&sControlCharVisibility,
+                               "layout.css.control-characters.visible");
 }
 
 nsCSSParser::nsCSSParser(mozilla::css::Loader* aLoader,
@@ -16049,3 +16052,12 @@ nsCSSParser::IsValueValidForProperty(const nsCSSProperty aPropID,
   return static_cast<CSSParserImpl*>(mImpl)->
     IsValueValidForProperty(aPropID, aPropValue);
 }
+
+/* static */
+uint8_t
+nsCSSParser::ControlCharVisibilityDefault()
+{
+  return sControlCharVisibility
+    ? NS_STYLE_CONTROL_CHARACTER_VISIBILITY_VISIBLE
+    : NS_STYLE_CONTROL_CHARACTER_VISIBILITY_HIDDEN;
+}

layout/style/nsCSSParser.h

@@ -314,6 +314,11 @@ public:
   bool IsValueValidForProperty(const nsCSSProperty aPropID,
                                const nsAString&    aPropValue);
 
+  // Return the default value to be used for -moz-control-character-visibility,
+  // from preferences (cached by our Startup(), so that both nsStyleText and
+  // nsRuleNode can have fast access to it).
+  static uint8_t ControlCharVisibilityDefault();
+
 protected:
   // This is a CSSParserImpl*, but if we expose that type name in this
   // header, we can't put the type definition (in nsCSSParser.cpp) in

layout/style/nsRuleNode.cpp

@@ -4379,7 +4379,7 @@ nsRuleNode::ComputeTextData(void* aStartStruct,
               conditions,
               SETDSC_ENUMERATED | SETDSC_UNSET_INHERIT,
               parentText->mControlCharacterVisibility,
-              NS_STYLE_CONTROL_CHARACTER_VISIBILITY_VISIBLE, 0, 0, 0, 0);
+              nsCSSParser::ControlCharVisibilityDefault(), 0, 0, 0, 0);
 
   COMPUTE_END_INHERITED(Text, text)
 }

layout/style/nsStyleStruct.cpp

@@ -16,6 +16,7 @@
 #include "nsPresContext.h"
 #include "nsIWidget.h"
 #include "nsCRTGlue.h"
+#include "nsCSSParser.h"
 #include "nsCSSProps.h"
 
 #include "nsCOMPtr.h"
@@ -3421,7 +3422,7 @@ nsStyleText::nsStyleText(void)
   mRubyPosition = NS_STYLE_RUBY_POSITION_OVER;
   mTextSizeAdjust = NS_STYLE_TEXT_SIZE_ADJUST_AUTO;
   mTextCombineUpright = NS_STYLE_TEXT_COMBINE_UPRIGHT_NONE;
-  mControlCharacterVisibility = NS_STYLE_CONTROL_CHARACTER_VISIBILITY_VISIBLE;
+  mControlCharacterVisibility = nsCSSParser::ControlCharVisibilityDefault();
 
   mLetterSpacing.SetNormalValue();
   mLineHeight.SetNormalValue();

modules/libpref/init/all.js

@@ -2394,6 +2394,13 @@ pref("layout.css.scroll-snap.enabled", true);
 // Is support for document.fonts enabled?
 pref("layout.css.font-loading-api.enabled", true);
 
+// Should stray control characters be rendered visibly?
+#ifdef RELEASE_BUILD
+pref("layout.css.control-characters.visible", false);
+#else
+pref("layout.css.control-characters.visible", true);
+#endif
+
 // pref for which side vertical scrollbars should be on
 // 0 = end-side in UI direction
 // 1 = end-side in document/content direction