IDEA-69452: "functions" namespace considered to be unsed even if it used in EL

xml/impl/src/com/intellij/xml/XmlExtension.java

@@ -202,9 +202,4 @@ public abstract class XmlExtension {
   public boolean isCustomTagAllowed(final XmlTag tag) {
     return false;
   }
-
-  @Nullable
-  public String[] getUsedPrefixes(XmlAttributeValue value) {
-    return null;
-  }
 }

xml/impl/src/com/intellij/xml/util/XmlRefCountHolder.java

@@ -22,6 +22,7 @@ import com.intellij.openapi.util.Pair;
 import com.intellij.openapi.util.UserDataCache;
 import com.intellij.psi.*;
 import com.intellij.psi.impl.source.resolve.reference.impl.providers.IdReferenceProvider;
+import com.intellij.psi.impl.source.xml.PossiblePrefixReference;
 import com.intellij.psi.impl.source.xml.SchemaPrefix;
 import com.intellij.psi.impl.source.xml.SchemaPrefixReference;
 import com.intellij.psi.templateLanguages.OuterLanguageElement;
@@ -34,7 +35,6 @@ import com.intellij.util.NullableFunction;
 import com.intellij.util.containers.ContainerUtil;
 import com.intellij.xml.XmlAttributeDescriptor;
 import com.intellij.xml.XmlElementDescriptor;
-import com.intellij.xml.XmlExtension;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -159,6 +159,15 @@ public class XmlRefCountHolder {
 
     private void visitOuterLanguageElement(@NotNull final PsiElement element) {
       myHolder.registerOuterLanguageElement(element);
+      PsiReference[] references = element.getReferences();
+      for (PsiReference reference : references) {
+        if (reference instanceof PossiblePrefixReference && ((PossiblePrefixReference)reference).isPrefixReference()) {
+          PsiElement resolve = reference.resolve();
+          if (resolve instanceof SchemaPrefix) {
+            myHolder.addUsedPrefix(((SchemaPrefix)resolve).getName());
+          }
+        }
+      }
     }
 
     @Override
@@ -226,12 +235,6 @@ public class XmlRefCountHolder {
             }
           }
         }
-        String[] prefixes = XmlExtension.getExtension(tag.getContainingFile()).getUsedPrefixes(value);
-        if (prefixes != null) {
-          for (String prefix : prefixes) {
-            myHolder.addUsedPrefix(prefix);
-          }
-        }
       }
 
       if (attributeDescriptor.hasIdRefType() && PsiTreeUtil.getChildOfType(value, OuterLanguageElement.class) == null) {