ENH: Enforce unique binary directories

The second argument of add_subdirectory must name a unique binary
directory or the build files will clobber each other.  This enforces
uniqueness with an error message.

Source/cmGlobalGenerator.cxx

@@ -732,18 +732,22 @@ void cmGlobalGenerator::Configure()
   this->ProjectMap.clear();
   this->RuleHashes.clear();
   this->DirectoryContentMap.clear();
+  this->BinaryDirectories.clear();
 
   // start with this directory
   cmLocalGenerator *lg = this->CreateLocalGenerator();
   this->LocalGenerators.push_back(lg);
 
   // set the Start directories
+  cmMakefile* mf = lg->GetMakefile();
   lg->GetMakefile()->SetStartDirectory
     (this->CMakeInstance->GetStartDirectory());
   lg->GetMakefile()->SetStartOutputDirectory
     (this->CMakeInstance->GetStartOutputDirectory());
   lg->GetMakefile()->MakeStartDirectoriesCurrent();
 
+  this->BinaryDirectories.insert(mf->GetStartOutputDirectory());
+
   // now do it
   lg->Configure();
 

Source/cmGlobalGenerator.h

@@ -253,6 +253,12 @@ public:
   void AddRuleHash(const std::vector<std::string>& outputs,
                    std::string const& content);
 
+  /** Return whether the given binary directory is unused.  */
+  bool BinaryDirectoryIsNew(const char* dir)
+    {
+    return this->BinaryDirectories.insert(dir).second;
+    }
+
 protected:
   // for a project collect all its targets by following depend
   // information, and also collect all the targets
@@ -350,6 +356,9 @@ private:
       derived(dc), LoadedFromDisk(dc.LoadedFromDisk) {}
   };
   std::map<cmStdString, DirectoryContent> DirectoryContentMap;
+
+  // Set of binary directories on disk.
+  std::set<cmStdString> BinaryDirectories;
 };
 
 #endif

Source/cmMakefile.cxx

@@ -1536,6 +1536,21 @@ void cmMakefile::AddSubDirectory(const char* srcPath, const char *binPath,
       }
     }
 
+  // Make sure the binary directory is unique.
+  cmGlobalGenerator* gg = this->LocalGenerator->GetGlobalGenerator();
+  if(!gg->BinaryDirectoryIsNew(binPath))
+    {
+    cmOStringStream e;
+    e << "The binary directory\n"
+      << "  " << binPath << "\n"
+      << "is already used to build another source directory, so it cannot "
+      << "be used to build source directory\n"
+      << "  " << srcPath << "\n"
+      << "Specify a unique binary directory name.";
+    this->IssueMessage(cmake::FATAL_ERROR, e.str());
+    return;
+    }
+
   // create a new local generator and set its parent
   cmLocalGenerator *lg2 =
     this->LocalGenerator->GetGlobalGenerator()->CreateLocalGenerator();