Test helper to show demangled C++ names

Heureka! found out that the C++ standard library exposes a
cross vendor C++ ABI, which amongst others allows to show
object code names and type-IDs in the language-level, human
readable unmangeld form.

Of course, actual application code should not rely on such a
internal representation, yet it is of tremendous help when
writing and debugging unit tests.

Signed-off-by: Ichthyostega <prg@ichthyostega.de>

research/try.cpp

@@ -26,21 +26,11 @@
 // 5/14  - c++11 transition: detect empty function object
 // 7/14  - c++11 transition: std hash function vs. boost hash
 // 9/14  - variadic templates and perfect forwarding
+// 11/14 - pointer to member functions and name mangling
 
 
 /** @file try.cpp
- ** Investigation: pitfalls of "perfect forwarding".
- ** Find out about the corner cases where chained argument forwarding
- ** does not work as expected. The key point is to put close attention on the
- ** template parameters we're passing on to the next lower layer. It is crucial
- ** either to add the reference explicitly, or to have it included implicitly
- ** by relying on the way how template params are matched on function calls:
- ** - lvalue -> parameter becomes TY &
- ** - rvalue -> parameter becomes TY
- ** 
- ** In this final stage, the example shows what happens if we erroneously fail
- ** to take the variadic arguments by '&&' on forwarding: we end-up with a
- ** slicing copy to the base class.
+ ** Investigation: member function pointers, types and name mangling.
  **
  */
 
@@ -48,11 +38,12 @@
 #include "lib/util.hpp"
 
 #include <cstddef>
-#include <utility>
 #include <iostream>
-#include <functional>
 #include <string>
 
+using lib::test::showType;
+using lib::test::demangleCxx;
+
 using std::string;
 using std::cout;
 using std::endl;
@@ -60,21 +51,10 @@ using std::endl;
 class Interface
   {
   public:
-    Interface(){}
-    Interface(Interface const& o) { cout << "COPY.CT from "<<&o<<" !!!\n"; }
-    Interface(Interface const&& o) { cout << "MOVE.CT from "<<&o<<" !!!\n"; }
+    virtual ~Interface() { } ///< this is an interface
     
-    Interface&
-    operator= (Interface const& o) { cout << "COPY= from "<<&o<<" !!!\n"; return *this; }
-    Interface&
-    operator= (Interface const&& o) { cout << "MOVE= from "<<&o<<" !!!\n"; return *this; }
-    
-    
-    virtual ~Interface() { }
-    virtual string op()  const
-      {
-        return "happy SLICING";
-      }
+    virtual string moo()    =0;
+    virtual string boo()    =0;
   };
 
 class Impl
@@ -82,11 +62,8 @@ class Impl
   {
     string s_;
     
-    string
-    op()  const override
-      {
-        return s_;
-      }
+    string moo() { return s_ + " Moo"; }
+    string boo() { return s_ + " Boo"; }
     
   public:
     Impl(string ss ="IMP")
@@ -94,65 +71,27 @@ class Impl
       { }
   };
 
-template<typename X>
-string
-showRefRRefVal()
-{
-  return std::is_lvalue_reference<X>::value? " by REF"
-                                           : std::is_rvalue_reference<X>::value? " by MOVE": " VAL";
-}
 
-template<typename... XS>
-void
-diagnostics (string id, XS const&... xs)
-{
-  cout << "--"<<id<<"--\n"
-       << lib::test::showVariadicTypes<XS...>(xs...)
-       << "\n"
-       ;
-}
-
-
-void
-invoke (Interface const& ref)
-{
-  using Ty = Interface const&;
-  diagnostics<Ty> ("Invoke", ref);
-  cout << "instanceof Impl?" << bool(INSTANCEOF(Impl, &ref)) <<"\n";
-  cout << "________________"
-       << ref.op()
-       << "____\n";
-}
-
-template<class FUN, typename...ARG>
-void
-indirect_1 (FUN fun, ARG... args)  // NOTE: erroneously taking ARG as-is, which results in taking BY VALUE when used in the forwarding chain!
-{
-  diagnostics<ARG...> ("Indirect-1", args...);
-  fun (args...);
-}
-
-template<class FUN, typename...ARG>
-void
-indirect_2 (FUN fun, ARG&&... args)
-{
-  diagnostics<ARG&&...> ("Indirect-2", args...);
-  indirect_1 (fun, std::forward<ARG>(args)...);
-}
 
 
 int
 main (int, char**)
   {
     Impl obj;
-    Interface const& ref = obj;
+    Interface& ref = obj;
+    
+    typedef string (Interface::*Memfun) (void);
+    
     
     cout << "before call. Address... "<<&ref<<"\n";
     
-    std::function<void(Interface const&)> fun(invoke);
+    cout << ref.moo() << endl;
+    cout << ref.boo() << endl;
     
-    indirect_2 (fun, ref);
-    indirect_2 (fun, Impl("honk"));
+    Memfun memfun = &Interface::moo;
+    cout << demangleCxx (showType (memfun)) << endl;
+    cout << demangleCxx (showType(&Interface::moo)) << endl;
+    cout << (ref.*memfun) () << endl;
     
     cout <<  "\n.gulp.\n";
     

src/lib/test/suite.cpp

@@ -50,9 +50,11 @@ namespace test {
   using std::shared_ptr;
   using boost::algorithm::trim;
   
+  using util::cStr;
   using util::isnil;
   using util::contains;
   using lib::test::showType;
+  using lib::test::demangleCxx;
   
   typedef map<string, Launcher*> TestMap;
   typedef shared_ptr<TestMap>  PTestMap;
@@ -174,7 +176,7 @@ namespace test {
     {
       try 
         {
-          INFO (test, "++------------------- invoking TEST: %s", showType(theTest).c());
+          INFO (test, "++------------------- invoking TEST: %s", cStr(demangleCxx(showType(theTest))));
           theTest.run (cmdline);
           return Suite::TEST_OK;
         }

src/lib/test/test-helper.cpp

@@ -24,6 +24,11 @@
 #include "lib/test/test-helper.hpp"
 #include "lib/test/testdummy.hpp"
 #include "lib/format-string.hpp"
+#include "lib/unique-malloc-owner.hpp"
+
+#ifdef __GNUG__
+#include <cxxabi.h>
+#endif
 
 #include <string>
 
@@ -41,6 +46,64 @@ namespace test{
   }
   
   
+#ifdef __GNUG__
+  /**
+   * \par Implementation notes
+   * GCC / G++ subscribes to a cross-vendor ABI for C++, sometimes called the IA64 ABI
+   * because it happens to be the native ABI for that platform. It is summarised
+   * \link http://www.codesourcery.com/cxx-abi/ mentor-embedded \endlink
+   * along with the current specification. For users of GCC greater than or equal to 3.x,
+   * entry points are exposed through the standard library in \c <cxxabi.h>
+   * relies on a vendor neutral ABI for C++ compiled programs
+   * 
+   *     char* abi::__cxa_demangle(const char* mangled_name,
+   *                               char* output_buffer, size_t* length,
+   *                               int* status)
+   * 
+   * Parameters:
+   *  - \c mangled_name
+   *    NUL-terminated character string containing the name to be demangled.
+   *  - \c output_buffer
+   *    region of memory, allocated with \c malloc, of `*length` bytes,
+   *    into which the demangled name is stored. If \c output_buffer is not long enough,
+   *    it is expanded using \c realloc. output_buffer may instead be NULL; in that case,
+   *    the demangled name is placed in a region of memory allocated with \c malloc.
+   *  - \c length
+   *    If length is non-NULL, the length of the buffer containing the demangled name is placed in `*length`.
+   *  - \c status
+   *    error flag: `*status` is set to one of the following values:
+   *             
+   *             0: The demangling operation succeeded.
+   *             -1: A memory allocation failure occurred.
+   *             -2: mangled_name is not a valid name under the C++ ABI mangling rules.
+   *             -3: One of the arguments is invalid.
+   * 
+   * The function returns a pointer to the start of the NUL-terminated demangled name,
+   * or NULL if the demangling fails. The caller is responsible for deallocating
+   * this memory using \c free.
+   */
+  string
+  demangleCxx (Literal rawName)
+  {
+    int error = -4;
+    UniqueMallocOwner<char> demangled (abi::__cxa_demangle (rawName,
+                                                            NULL,
+                                                            NULL,
+                                                            &error));
+    return 0==error? demangled.get()
+                   : string(rawName);
+  }
+  
+#else
+  string
+  demangleCxx (Literal rawName)
+  {
+    return string (rawName);
+  }
+#endif
+  
+  
+  
   /** @todo probably this can be done in a more clever way. Anyone...?
    */
   string
@@ -55,7 +118,8 @@ namespace test{
       garbage[--p] = alpha[rand() % MAXAL];
     return garbage;
   }
-
+  
+  
   
   /** storage for test-dummy flags */
     

src/lib/test/test-helper.hpp

@@ -72,6 +72,19 @@ namespace test{
   }
   
   
+  /** reverse the effect of C++ name mangling.
+   * @return string in language-level form of a C++ type or object name,
+   *         or a string with the original input if demangling fails.
+   * @warning implementation relies on the cross vendor C++ ABI in use
+   *         by GCC and compatible compilers, so portability is limited.
+   *         The implementation is accessed through libStdC++
+   *         Name representation in emitted object code and type IDs is
+   *         essentially an implementation detail and subject to change.
+   */
+  string
+  demangleCxx (Literal rawName);
+  
+  
   /** for printing sizeof().
    *  prints the given size and name literally, without any further magic */
   string

tests/00support.tests

@@ -14,7 +14,13 @@ out: sizeof.+lib.+test.+test.+Wrmrmpft.+Murpf.+ =   1
 END
 
 
-TEST "TestOption_test" TestOption_test <<END
+TEST "Helper to show demangled C++ names" TestHelperDemangling_test <<END
+out: .+lib.test.test.Space.+Outer.+Inner
+out-lit: lib::test::test::Space const* (*)(lib::test::test::Outer<lib::test::test::Space>::Inner const&&)
+END
+
+
+TEST "Testsuite option handling" TestOption_test <<END
 out: Testing invocation with cmdline: ...
 out: --> Testgroup=ALL
 out: --> Test-ID  =--missing--

tests/library/test/test-helper-demangling-test.cpp

@@ -0,0 +1,80 @@
+/*
+  TestHelperDemangling(Test)  -  ensure a helper for C++ demangling works as expected
+
+  Copyright (C)         Lumiera.org
+    2014,               Hermann Vosseler <Ichthyostega@web.de>
+
+  This program is free software; you can redistribute it and/or
+  modify it under the terms of the GNU General Public License as
+  published by the Free Software Foundation; either version 2 of
+  the License, or (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+* *****************************************************/
+
+
+#include "lib/test/run.hpp"
+#include "lib/test/test-helper.hpp"
+
+#include <string>
+
+using std::string;
+using std::cout;
+using std::endl;
+
+
+namespace lib {
+namespace test{
+namespace test{
+  
+  template<class T>
+  struct Outer
+    {
+      struct Inner { };
+      
+      static const T*
+      phantom (Inner const&&)
+        {
+          return nullptr;
+        }
+    };
+  
+  struct Space { };
+  
+  
+  
+  
+  /**********************************************//**
+   * @test verify the demangling of C++ names,
+   *       as available through the GCC platform ABI.
+   *       The Lumiera support library exposes this
+   *       non-portable feature through a convenience
+   *       helper to ease the writing of unit tests.
+   *       
+   * @see test-helper.hpp
+   */
+  class TestHelperDemangling_test : public Test
+    {
+      void
+      run (Arg)
+        {
+          Outer<Space> ship;
+          auto magic = &ship.phantom;
+          
+          cout << showType(magic) << endl;
+          cout << demangleCxx(showType(magic)) << endl;
+        }
+    };
+  
+  LAUNCHER (TestHelperDemangling_test, "unit common");
+  
+  
+}}} // namespace lib::test::test