C++: Limit template instantiation depth

A recursive template generates infinite expansions.

Consider the following example:

template <class R1>
struct Base
{
};

template<typename R>
struct Derived :
  Base<
    typename Derived<typename Base<R>::type>::type,
    typename Derived<typename Base<R>::type>::type
  >::type
{};

R is instantiated as Base<R>::type, which causes another
instantiation of R into Base<Base<R>> etc...

This is not a solution, but a workaround.

Task-number: QTCREATORBUG-15141
Change-Id: Ib04f70275e07919e2cb6c7fb61a2045bd52f4a7d
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/libs/cplusplus/LookupContext.cpp

@@ -1549,6 +1549,7 @@ CreateBindings::CreateBindings(Document::Ptr thisDocument, const Snapshot &snaps
     : _snapshot(snapshot)
     , _control(QSharedPointer<Control>(new Control))
     , _expandTemplates(false)
+    , _depth(0)
 {
     _globalNamespace = allocLookupScope(/*parent = */ 0, /*name = */ 0);
     _currentLookupScope = _globalNamespace;
@@ -1978,8 +1979,13 @@ void CreateBindings::initializeSubst(Clone &cloner,
 {
     const unsigned argumentCountOfSpecialization = specialization->templateParameterCount();
 
+    if (_depth > 15)
+        return;
+
+    ++_depth;
     for (unsigned i = 0; i < argumentCountOfSpecialization; ++i)
         resolveTemplateArgument(cloner, subst, origin, specialization, instantiation, i);
+    --_depth;
 }
 
 } // namespace CPlusPlus

src/libs/cplusplus/LookupContext.h

@@ -209,6 +209,7 @@ private:
     LookupScope *_globalNamespace;
     LookupScope *_currentLookupScope;
     bool _expandTemplates;
+    int _depth;
 };
 
 class CPLUSPLUS_EXPORT LookupContext

tests/auto/cplusplus/checksymbols/tst_checksymbols.cpp

@@ -225,6 +225,8 @@ private slots:
     void test_checksymbols_infiniteLoop_data();
     void test_checksymbols_infiniteLoop();
 
+    void test_checksymbols_infiniteLoop_BUG15141();
+
     void test_parentOfBlock();
 
     void findField();
@@ -1122,6 +1124,25 @@ void tst_CheckSymbols::test_checksymbols_infiniteLoop()
     TestCase::runCheckSymbols(document1, snapshot);
 }
 
+void tst_CheckSymbols::test_checksymbols_infiniteLoop_BUG15141()
+{
+    QByteArray source =
+            "template <class R1>\n"
+            "struct Base\n"
+            "{\n"
+            "};\n"
+            "\n"
+            "template<typename R>\n"
+            "struct Derived :\n"
+            "  Base<\n"
+            "    typename Derived<typename Base<R>::type>::type,\n"
+            "    typename Derived<typename Base<R>::type>::type\n"
+            "  >::type\n"
+            "{};\n";
+
+    BaseTestCase tc(source);
+}
+
 void tst_CheckSymbols::test_parentOfBlock()
 {
     const QByteArray source = "void C::f()\n"