Fix compilation with libc++

libc++ (http://libcxx.llvm.org/) is used on OS X with newer XCode.
The patch is from Benjamin Piwowarski <benjamin.piwowarski@lip6.fr>, I only
added more comments.
The changes regarding implicit conversion to bool of std::iostream work
because both the C++98 and C++11 standards guarantee that boolean evaluation
of streams returns !fail(). See e.g.
http://stackoverflow.com/questions/1334858/why-dont-iostream-objects-overload-operator-bool
for details.

src/Buffer.cpp

@@ -994,7 +994,8 @@ bool Buffer::importString(string const & format, docstring const & contents, Err
 	TempFile const tempfile("Buffer_importStringXXXXXX." + fmt->extension());
 	FileName const name(tempfile.name());
 	ofdocstream os(name.toFilesystemEncoding().c_str());
-	bool const success = (os << contents);
+	// Do not convert os implicitly to bool, since that is forbidden in C++11.
+	bool const success = !(os << contents).fail();
 	os.close();
 
 	bool converted = false;

src/mathed/MathExtern.cpp

@@ -1472,7 +1472,8 @@ bool extractNumber(MathData const & ar, int & i)
 {
 	idocstringstream is(charSequence(ar.begin(), ar.end()));
 	is >> i;
-	return is;
+	// Do not convert is implicitly to bool, since that is forbidden in C++11.
+	return !is.fail();
 }
 
 
@@ -1480,7 +1481,8 @@ bool extractNumber(MathData const & ar, double & d)
 {
 	idocstringstream is(charSequence(ar.begin(), ar.end()));
 	is >> d;
-	return is;
+	// Do not convert is implicitly to bool, since that is forbidden in C++11.
+	return !is.fail();
 }
 
 

src/support/debug.h

@@ -17,6 +17,10 @@
 
 #include "support/strfwd.h"
 
+// Forward definitions do not work with libc++
+// but ios_base has already been defined in strfwd
+// if compiling with it
+#ifndef  _LIBCPP_VERSION
 namespace std {
 
 class ios_base;
@@ -25,6 +29,7 @@ template<typename CharT, typename Traits> class basic_streambuf;
 typedef basic_streambuf<char, char_traits<char> > streambuf;
 
 }
+#endif
 
 
 namespace lyx {

src/support/strfwd.h

@@ -13,6 +13,14 @@
 #ifndef STRFWD_H
 #define STRFWD_H
 
+// This includes does nothing but defining _LIBCPP_VERSION
+// if libc++ is used (rather than libstdc++) - we first
+// check if we have at least a c++03 standard before
+// including the file
+#if (__cplusplus > 19971L)
+#include <ciso646>
+#endif
+
 #ifdef USE_WCHAR_T
 
 // Prefer this if possible because GNU libstdc++ has usable
@@ -28,6 +36,10 @@ namespace lyx { typedef boost::uint32_t char_type; }
 
 #endif
 
+// Forward definitions do not work with libc++
+#ifdef  _LIBCPP_VERSION
+#include <string>
+#else
 
 namespace std {
 
@@ -52,6 +64,7 @@ typedef basic_ostringstream<char, char_traits<char>, allocator<char> > ostringst
 
 } // namepace std
 
+#endif
 
 namespace lyx {
 

src/tex2lyx/Parser.h

@@ -125,8 +125,10 @@ public:
 
 	iparserdocstream(idocstream & is) : is_(is) {}
 
-	/// Like std::istream::operator bool()
-	operator bool() const { return s_.empty() ? is_ : true; }
+	/// Like std::istream::operator void*()
+	/// Do not convert is_ implicitly to bool, since that is forbidden in C++11.
+	/// FIXME: Convert to operator void*() in LyX 2.2
+	operator bool() const { return s_.empty() ? !is_.fail() : true; }
 
 	/// change the encoding of the input stream to \p e (iconv name)
 	void setEncoding(std::string const & e);