C++: Make 'follow symbol' work with forward declared classes.

If it encounters a forward declaration, it tries to find the class
declaration globally now.

Task-number: QTCREATORBUG-20

src/libs/cplusplus/CppDocument.cpp

@@ -793,3 +793,26 @@ Symbol *Snapshot::findMatchingDefinition(Symbol *symbol) const
 
     return 0;
 }
+
+Class *Snapshot::findMatchingClassDeclaration(Symbol *declaration) const
+{
+    if (! declaration->identifier())
+        return 0;
+
+    foreach (Document::Ptr doc, *this) {
+        if (! doc->control()->findIdentifier(declaration->identifier()->chars(),
+                                             declaration->identifier()->size()))
+            continue;
+
+        LookupContext context(doc, *this);
+
+        ClassOrNamespace *type = context.lookupType(declaration);
+        if (!type || type->symbols().count() != 1)
+            continue;
+
+        if (Class *c = type->symbols().first()->asClass())
+            return c;
+    }
+
+    return 0;
+}

src/libs/cplusplus/CppDocument.h

@@ -372,6 +372,7 @@ public:
                                      const QString &fileName) const;
 
     Symbol *findMatchingDefinition(Symbol *symbol) const;
+    Class *findMatchingClassDeclaration(Symbol *symbol) const;
 
 private:
     void simplified_helper(Document::Ptr doc, Snapshot *snapshot) const;

src/libs/cplusplus/LookupContext.cpp

@@ -64,7 +64,8 @@ static void fullyQualifiedName_helper(Symbol *symbol, QList<const Name *> *names
                 names->append(symbol->name());
             }
         } else if (symbol->isObjCClass() || symbol->isObjCBaseClass() || symbol->isObjCProtocol()
-                || symbol->isObjCForwardClassDeclaration() || symbol->isObjCForwardProtocolDeclaration()) {
+                || symbol->isObjCForwardClassDeclaration() || symbol->isObjCForwardProtocolDeclaration()
+                || symbol->isForwardClassDeclaration()) {
             if (symbol->name())
                 names->append(symbol->name());
         } else if (symbol->isFunction()) {

src/plugins/cppeditor/cppeditor.cpp

@@ -1315,6 +1315,10 @@ CPPEditor::Link CPPEditor::findLinkAt(const QTextCursor &cursor,
                     def = 0; // jump to declaration then.
             }
 
+            if (symbol->isForwardClassDeclaration()) {
+                def = snapshot.findMatchingClassDeclaration(symbol);
+            }
+
             link = linkToSymbol(def ? def : symbol);
             link.begin = beginOfToken;
             link.end = endOfToken;