ENH: Create CMP0013 to disallow duplicate dirs

In CMake 2.6.3 and below we silently accepted duplicate build
directories whose build files would then conflict.  At first this was
considured purely a bug that confused beginners but would not be used in
a real project.  In CMake 2.6.4 we explicitly made it an error.

However, some real projects took advantage of this as a "feature" and
got lucky that the subtle build errors it can cause did not occur.
Therefore we need a policy to deal with the case more gracefully.
See issue #9173.

1 files changed, 2 insertions, 0 deletions

diff --git a/Source/cmMakefile.h b/Source/cmMakefile.h
index 5efe2d9..7a235f9 100644
--- a/Source/cmMakefile.h
+++ b/Source/cmMakefile.h
@@ -900,6 +900,8 @@ private:
 
   bool ParseDefineFlag(std::string const& definition, bool remove);
 
+  bool EnforceUniqueDir(const char* srcPath, const char* binPath);
+
   void ReadSources(std::ifstream& fin, bool t);
   friend class cmMakeDepend;    // make depend needs direct access
                                 // to the Sources array