Build object library targets in Ninja

Treat OBJECT libraries as STATIC libraries but leave out the archive
step.  The object files will be left behind for reference by other
targets later.

Source/cmGlobalNinjaGenerator.cxx

@@ -664,6 +664,7 @@ cmGlobalNinjaGenerator
       target->GetFullPath(configName).c_str()));
     break;
 
+  case cmTarget::OBJECT_LIBRARY:
   case cmTarget::UTILITY: {
     std::string path = ng->ConvertToNinjaPath(
       target->GetMakefile()->GetStartOutputDirectory());

Source/cmNinjaNormalTargetGenerator.cxx

@@ -43,10 +43,13 @@ cmNinjaNormalTargetGenerator(cmTarget* target)
                             this->TargetNamePDB,
                             GetLocalGenerator()->GetConfigName());
 
+  if(target->GetType() != cmTarget::OBJECT_LIBRARY)
+    {
     // on Windows the output dir is already needed at compile time
     // ensure the directory exists (OutDir test)
     std::string outpath = target->GetDirectory(this->GetConfigName());
     cmSystemTools::MakeDirectory(outpath.c_str());
+    }
 }
 
 cmNinjaNormalTargetGenerator::~cmNinjaNormalTargetGenerator()
@@ -67,8 +70,15 @@ void cmNinjaNormalTargetGenerator::Generate()
   // Write the build statements
   this->WriteObjectBuildStatements();
 
+  if(this->GetTarget()->GetType() == cmTarget::OBJECT_LIBRARY)
+    {
+    this->WriteObjectLibStatement();
+    }
+  else
+    {
     this->WriteLinkRule();
     this->WriteLinkStatement();
+    }
 
   this->GetBuildFileStream() << "\n";
   this->GetRulesFileStream() << "\n";
@@ -467,3 +477,21 @@ void cmNinjaNormalTargetGenerator::WriteLinkStatement()
   this->GetGlobalGenerator()->AddTargetAlias(this->GetTargetName(),
                                              this->GetTarget());
 }
+
+//----------------------------------------------------------------------------
+void cmNinjaNormalTargetGenerator::WriteObjectLibStatement()
+{
+  // Write a phony output that depends on all object files.
+  cmNinjaDeps outputs;
+  this->GetLocalGenerator()->AppendTargetOutputs(this->GetTarget(), outputs);
+  cmNinjaDeps depends = this->GetObjects();
+  cmGlobalNinjaGenerator::WritePhonyBuild(this->GetBuildFileStream(),
+                                          "Object library "
+                                          + this->GetTargetName(),
+                                          outputs,
+                                          depends);
+
+  // Add aliases for the target name.
+  this->GetGlobalGenerator()->AddTargetAlias(this->GetTargetName(),
+                                             this->GetTarget());
+}

Source/cmNinjaNormalTargetGenerator.h

@@ -32,6 +32,7 @@ private:
   void WriteLanguagesRules();
   void WriteLinkRule();
   void WriteLinkStatement();
+  void WriteObjectLibStatement();
   std::vector<std::string> ComputeLinkCmd();
 
 private:

Source/cmNinjaTargetGenerator.cxx

@@ -34,6 +34,7 @@ cmNinjaTargetGenerator::New(cmTarget* target)
       case cmTarget::SHARED_LIBRARY:
       case cmTarget::STATIC_LIBRARY:
       case cmTarget::MODULE_LIBRARY:
+      case cmTarget::OBJECT_LIBRARY:
         return new cmNinjaNormalTargetGenerator(target);
 
       case cmTarget::UTILITY:
@@ -221,7 +222,8 @@ ComputeDefines(cmSourceFile *source, const std::string& language)
 cmNinjaDeps cmNinjaTargetGenerator::ComputeLinkDeps() const
 {
   // Static libraries never depend on other targets for linking.
-  if (this->Target->GetType() == cmTarget::STATIC_LIBRARY)
+  if (this->Target->GetType() == cmTarget::STATIC_LIBRARY ||
+      this->Target->GetType() == cmTarget::OBJECT_LIBRARY)
     return cmNinjaDeps();
 
   cmComputeLinkInformation* cli =