Alert! MissingMathML fonts. Here goes the prompt that the user will see when it is detected that crucial stretchy MathML fonts are not installed. The list of those fonts that are missing is shown so that the user can install them. The message is hardcoded and would need to be localized

layout/mathml/base/src/Makefile.in

@@ -41,6 +41,7 @@ REQUIRES	= xpcom \
 		  necko \
 		  docshell \
 		  webbrwsr \
+		  windowwatcher \
 		  pref \
 		  $(NULL)
 

layout/mathml/base/src/makefile.win

@@ -36,6 +36,7 @@ REQUIRES    = xpcom \
 			  view \
 			  docshell \
 			  webbrowser_core \
+			  windowwatcher \
 			  pref \
               $(NULL)
 

layout/mathml/base/src/nsMathMLChar.cpp

@@ -50,6 +50,9 @@
 #include "nsCSSRendering.h"
 #include "prprf.h"         // For PR_snprintf()
 
+#include "nsIWindowWatcher.h"
+#include "nsIPrompt.h"
+
 #include "nsMathMLOperators.h"
 #include "nsMathMLChar.h"
 
@@ -116,7 +119,7 @@ static nsCOMPtr<nsIPersistentProperties> gPUAProperties;
 
 // helper to check if a font is installed
 static PRBool
-CheckFontExistence(nsIPresContext* aPresContext, nsString& aFontName)
+CheckFontExistence(nsIPresContext* aPresContext, const nsString& aFontName)
 {
   PRBool aliased;
   nsAutoString localName;
@@ -128,6 +131,28 @@ CheckFontExistence(nsIPresContext* aPresContext, nsString& aFontName)
   return rv;
 }
 
+// alert the user if some of the needed MathML fonts are not installed.
+void
+AlertMissingFonts(nsString& aMissingFonts)
+{
+  nsCOMPtr<nsIWindowWatcher> wwatch(do_GetService("@mozilla.org/embedcomp/window-watcher;1"));
+  nsCOMPtr<nsIPrompt> prompter;
+  if (wwatch) {
+    wwatch->GetNewPrompter(0, getter_AddRefs(prompter));
+    if (prompter) {
+      nsAutoString message;
+      message.AssignWithConversion(
+"This page contains MathML. Mozilla has detected that some "
+"of the fonts needed for quality rendering of MathML are missing "
+"from your system. Without these fonts, Mozilla cannot render "
+"the page properly. To get a rendering of professional quality "
+"you should install the following fonts: ");
+      message.Append(aMissingFonts);
+      prompter->Alert(0, message.get());
+    }
+  }
+}
+
 // helper to trim off comments from data in a MathFont Property File
 static void
 Clean(nsString& aValue)
@@ -997,16 +1022,39 @@ SetPreferredTableList(PRUnichar aChar, nsString& aExtension, nsString& aFamilyLi
   }
 }
 
+struct MathFontEnumContext {
+  nsIPresContext* mPresContext;
+  nsString*       mMissingFamilyList;
+};
+
 static PRBool PR_CALLBACK
 MathFontEnumCallback(const nsString& aFamily, PRBool aGeneric, void *aData)
 {
+  // check if the font is missing
+  MathFontEnumContext* context = (MathFontEnumContext*)aData;
+  nsIPresContext* presContext = context->mPresContext;
+  nsString* missingFamilyList = context->mMissingFamilyList;
+  if (!CheckFontExistence(presContext, aFamily)) {
+//#ifndef _WIN32
+   // XXX In principle, the mathfont-family list in the mathfont.properties file
+   // is customizable depending on the platform. For now, this is here since there
+   // is no need to alter Linux users about TrueType fonts specific to Windows.
+   if (aFamily.EqualsIgnoreCase("MT Extra"))
+     return PR_TRUE; // continue to try other fonts
+//#endif
+    if (!missingFamilyList->IsEmpty()) {
+      missingFamilyList->Append(NS_LITERAL_STRING(", "));
+    }
+    missingFamilyList->Append(aFamily);
+  }
+
   if (!gGlyphTableList->AddGlyphTable(aFamily))
     return PR_FALSE; // stop in low-memory situations
   return PR_TRUE; // don't stop
 }
 
 static nsresult
-InitGlobals()
+InitGlobals(nsIPresContext* aPresContext)
 {
   NS_ASSERTION(!gInitialized, "Error -- already initialized");
   gInitialized = PR_TRUE;
@@ -1085,10 +1133,17 @@ InitGlobals()
   }
 
   // Parse the font list and append an entry for each family to gGlyphTableList
-  font.EnumerateFamilies(MathFontEnumCallback, gGlyphTableList);
+  nsAutoString missingFamilyList;
+  MathFontEnumContext context = {aPresContext, &missingFamilyList};
+  font.EnumerateFamilies(MathFontEnumCallback, &context);
   // Append a null separator
   gGlyphTableList->AppendTable(nsnull);
 
+  // alert the user if some of the expected fonts are missing
+  if (!missingFamilyList.IsEmpty()) {
+    AlertMissingFonts(missingFamilyList);
+  }
+
   // Let the particular characters have their preferred extension tables
   nsCOMPtr<nsISimpleEnumerator> iterator;
   if (NS_SUCCEEDED(mathfontProp->SimpleEnumerateProperties(getter_AddRefs(iterator)))) {
@@ -1154,7 +1209,7 @@ nsMathMLChar::SetData(nsIPresContext* aPresContext,
 {
   NS_ASSERTION(!mParent, "invalid call - not allowed for child chars");
   if (!gInitialized) {
-    InitGlobals();
+    InitGlobals(aPresContext);
   }
   mData = aData;
   // some assumptions until proven otherwise