ENH: add OPTIONAL keyword to ENABLE_LANGUAGE, so it will be possible to do

something like this:

ENABLE_LANGUAGE(ASM-ATT)
IF(CMAKE_ASM-ATT_COMPILER_WORKS)
  ... do assembler stufff
ELSE(CMAKE_ASM-ATT_COMPILER_WORKS)
  ... fallback to generic C/C++
ENDIF(CMAKE_ASM-ATT_COMPILER_WORKS)

Alex

Source/cmEnableLanguageCommand.cxx

@@ -20,13 +20,29 @@
 bool cmEnableLanguageCommand
 ::InitialPass(std::vector<std::string> const& args)
 {
+  bool optional = false;
+  std::vector<std::string> languages;
   if(args.size() < 1 )
     {
     this->SetError
       ("ENABLE_LANGUAGE called with incorrect number of arguments");
     return false;
     } 
-  this->Makefile->EnableLanguage(args);
+  for (std::vector<std::string>::const_iterator it = args.begin();
+       it != args.end();
+       ++it)
+    {
+    if ((*it) == "OPTIONAL")
+      {
+      optional = true;
+      }
+    else
+      {
+      languages.push_back(*it);
+      }
+    }
+
+  this->Makefile->EnableLanguage(languages, optional);
   return true;
 }
 

Source/cmEnableLanguageCommand.h

@@ -63,11 +63,13 @@ public:
   virtual const char* GetFullDocumentation()
     {
     return
-      "  ENABLE_LANGUAGE(languageName)\n"
+      "  ENABLE_LANGUAGE(languageName [OPTIONAL] )\n"
       "This command enables support for the named language in CMake. "
       "This is the same as the project command but does not create "
       "any of the extra varaibles that are created by the project command. "
-      "Example languages are CXX, C, Fortran.";
+      "Example languages are CXX, C, Fortran.\n"
+      "If OPTIONAL is used, use the CMAKE_<languageName>_COMPILER_WORKS "
+      "variable to check whether the language has been enabled successfully.";
     }
   
   cmTypeMacro(cmEnableLanguageCommand, cmCommand);

Source/cmGlobalBorlandMakefileGenerator.cxx

@@ -30,13 +30,15 @@ cmGlobalBorlandMakefileGenerator::cmGlobalBorlandMakefileGenerator()
 
 
 void cmGlobalBorlandMakefileGenerator
-::EnableLanguage(std::vector<std::string>const& l, cmMakefile *mf)
+::EnableLanguage(std::vector<std::string>const& l, 
+                 cmMakefile *mf, 
+                 bool optional)
 {
   std::string outdir = this->CMakeInstance->GetStartOutputDirectory();
   mf->AddDefinition("BORLAND", "1");
   mf->AddDefinition("CMAKE_GENERATOR_CC", "bcc32");
   mf->AddDefinition("CMAKE_GENERATOR_CXX", "bcc32"); 
-  this->cmGlobalUnixMakefileGenerator3::EnableLanguage(l, mf);
+  this->cmGlobalUnixMakefileGenerator3::EnableLanguage(l, mf, optional);
 }
 
 ///! Create a local generator appropriate to this Global Generator

Source/cmGlobalBorlandMakefileGenerator.h

@@ -47,7 +47,7 @@ public:
    * extension, pthreads, byte order etc.  
    */
   virtual void EnableLanguage(std::vector<std::string>const& languages,
-                              cmMakefile *);
+                              cmMakefile *, bool optional);
 };
 
 #endif

Source/cmGlobalGenerator.cxx

@@ -196,7 +196,7 @@ void cmGlobalGenerator::FindMakeProgram(cmMakefile* mf)
 
 void
 cmGlobalGenerator::EnableLanguage(std::vector<std::string>const& languages,
-                                  cmMakefile *mf)
+                                  cmMakefile *mf, bool optional)
 {
   if(languages.size() == 0)
     {

Source/cmGlobalGenerator.h

@@ -77,7 +77,7 @@ public:
    * extension, pthreads, byte order etc.  
    */
   virtual void EnableLanguage(std::vector<std::string>const& languages,
-                              cmMakefile *);
+                              cmMakefile *, bool optional);
 
   /**
    * Try to determine system infomation, get it from another generator

Source/cmGlobalMSYSMakefileGenerator.cxx

@@ -50,7 +50,9 @@ cmGlobalMSYSMakefileGenerator::FindMinGW(std::string const& makeloc)
 }
 
 void cmGlobalMSYSMakefileGenerator
-::EnableLanguage(std::vector<std::string>const& l, cmMakefile *mf)
+::EnableLanguage(std::vector<std::string>const& l, 
+                 cmMakefile *mf, 
+                 bool optional)
 {
   this->FindMakeProgram(mf);
   std::string makeProgram = mf->GetRequiredDefinition("CMAKE_MAKE_PROGRAM");
@@ -75,7 +77,7 @@ void cmGlobalMSYSMakefileGenerator
   mf->AddDefinition("MSYS", "1");
   mf->AddDefinition("CMAKE_GENERATOR_CC", gcc.c_str());
   mf->AddDefinition("CMAKE_GENERATOR_CXX", gxx.c_str());
-  this->cmGlobalUnixMakefileGenerator3::EnableLanguage(l, mf);
+  this->cmGlobalUnixMakefileGenerator3::EnableLanguage(l, mf, optional);
   if(!mf->IsSet("CMAKE_AR") && !this->CMakeInstance->GetIsInTryCompile())
     {
     cmSystemTools::Error

Source/cmGlobalMSYSMakefileGenerator.h

@@ -47,7 +47,7 @@ public:
    * extension, pthreads, byte order etc.  
    */
   virtual void EnableLanguage(std::vector<std::string>const& languages,
-                              cmMakefile *);
+                              cmMakefile *, bool optional);
 
 private:
   std::string FindMinGW(std::string const& makeloc);

Source/cmGlobalMinGWMakefileGenerator.cxx

@@ -27,7 +27,9 @@ cmGlobalMinGWMakefileGenerator::cmGlobalMinGWMakefileGenerator()
 }
 
 void cmGlobalMinGWMakefileGenerator
-::EnableLanguage(std::vector<std::string>const& l, cmMakefile *mf)
+::EnableLanguage(std::vector<std::string>const& l, 
+                 cmMakefile *mf, 
+                 bool optional)
 { 
   this->FindMakeProgram(mf);
   std::string makeProgram = mf->GetRequiredDefinition("CMAKE_MAKE_PROGRAM");
@@ -49,7 +51,7 @@ void cmGlobalMinGWMakefileGenerator
     }
   mf->AddDefinition("CMAKE_GENERATOR_CC", gcc.c_str());
   mf->AddDefinition("CMAKE_GENERATOR_CXX", gxx.c_str());
-  this->cmGlobalUnixMakefileGenerator3::EnableLanguage(l, mf);
+  this->cmGlobalUnixMakefileGenerator3::EnableLanguage(l, mf, optional);
 }
 
 ///! Create a local generator appropriate to this Global Generator

Source/cmGlobalMinGWMakefileGenerator.h

@@ -46,7 +46,7 @@ public:
    * extension, pthreads, byte order etc.  
    */
   virtual void EnableLanguage(std::vector<std::string>const& languages,
-                              cmMakefile *);
+                              cmMakefile *, bool optional);
 };
 
 #endif

Source/cmGlobalNMakeMakefileGenerator.cxx

@@ -27,12 +27,14 @@ cmGlobalNMakeMakefileGenerator::cmGlobalNMakeMakefileGenerator()
 }
 
 void cmGlobalNMakeMakefileGenerator
-::EnableLanguage(std::vector<std::string>const& l, cmMakefile *mf)
+::EnableLanguage(std::vector<std::string>const& l, 
+                 cmMakefile *mf, 
+                 bool optional)
 {
   // pick a default 
   mf->AddDefinition("CMAKE_GENERATOR_CC", "cl");
   mf->AddDefinition("CMAKE_GENERATOR_CXX", "cl");
-  this->cmGlobalUnixMakefileGenerator3::EnableLanguage(l, mf);
+  this->cmGlobalUnixMakefileGenerator3::EnableLanguage(l, mf, optional);
 }
 
 ///! Create a local generator appropriate to this Global Generator

Source/cmGlobalNMakeMakefileGenerator.h

@@ -46,7 +46,7 @@ public:
    * extension, pthreads, byte order etc.  
    */
   virtual void EnableLanguage(std::vector<std::string>const& languages,
-                              cmMakefile *);
+                              cmMakefile *, bool optional);
 };
 
 #endif

Source/cmGlobalUnixMakefileGenerator3.cxx

@@ -39,9 +39,11 @@ cmGlobalUnixMakefileGenerator3::cmGlobalUnixMakefileGenerator3()
 }
 
 void cmGlobalUnixMakefileGenerator3
-::EnableLanguage(std::vector<std::string>const& languages, cmMakefile *mf)
+::EnableLanguage(std::vector<std::string>const& languages, 
+                 cmMakefile *mf, 
+                 bool optional)
 {
-  this->cmGlobalGenerator::EnableLanguage(languages, mf);
+  this->cmGlobalGenerator::EnableLanguage(languages, mf, optional);
   std::string path;
   for(std::vector<std::string>::const_iterator l = languages.begin();
       l != languages.end(); ++l)
@@ -70,7 +72,8 @@ void cmGlobalUnixMakefileGenerator3
       {
       path = name;
       }
-    if(path.size() == 0 || !cmSystemTools::FileExists(path.c_str()))
+    if((path.size() == 0 || !cmSystemTools::FileExists(path.c_str())) 
+        && (optional==false))
       {
       std::string message = "your ";
       message += lang;

Source/cmGlobalUnixMakefileGenerator3.h

@@ -77,7 +77,7 @@ public:
    * extension, pthreads, byte order etc.  
    */
   virtual void EnableLanguage(std::vector<std::string>const& languages,
-                              cmMakefile *);
+                              cmMakefile *, bool optional);
 
   /**
    * Generate the all required files for building this project/tree. This

Source/cmGlobalVisualStudio6Generator.cxx

@@ -25,7 +25,9 @@ cmGlobalVisualStudio6Generator::cmGlobalVisualStudio6Generator()
 }
 
 void cmGlobalVisualStudio6Generator
-::EnableLanguage(std::vector<std::string>const& lang, cmMakefile *mf)
+::EnableLanguage(std::vector<std::string>const& lang, 
+                 cmMakefile *mf, 
+                 bool options)
 {
   mf->AddDefinition("CMAKE_GENERATOR_CC", "cl");
   mf->AddDefinition("CMAKE_GENERATOR_CXX", "cl");
@@ -34,7 +36,7 @@ void cmGlobalVisualStudio6Generator
   mf->AddDefinition("CMAKE_GENERATOR_Fortran", "ifort");
   mf->AddDefinition("MSVC60", "1");
   this->GenerateConfigurations(mf);
-  this->cmGlobalGenerator::EnableLanguage(lang, mf);
+  this->cmGlobalGenerator::EnableLanguage(lang, mf, optional);
 }
 
 void cmGlobalVisualStudio6Generator::GenerateConfigurations(cmMakefile* mf)

Source/cmGlobalVisualStudio6Generator.h

@@ -49,7 +49,7 @@ public:
    * extension, pthreads, byte order etc.  
    */
   virtual void EnableLanguage(std::vector<std::string>const& languages, 
-                              cmMakefile *);
+                              cmMakefile *, bool optional);
 
   /**
    * Try running cmake and building a file. This is used for dynalically

Source/cmGlobalVisualStudio7Generator.cxx

@@ -29,7 +29,7 @@ cmGlobalVisualStudio7Generator::cmGlobalVisualStudio7Generator()
 
 void cmGlobalVisualStudio7Generator
 ::EnableLanguage(std::vector<std::string>const &  lang, 
-                 cmMakefile *mf)
+                 cmMakefile *mf, bool optional)
 {
   mf->AddDefinition("CMAKE_GENERATOR_CC", "cl");
   mf->AddDefinition("CMAKE_GENERATOR_CXX", "cl");
@@ -40,7 +40,7 @@ void cmGlobalVisualStudio7Generator
   this->AddPlatformDefinitions(mf);
   
   // Create list of configurations requested by user's cache, if any.
-  this->cmGlobalGenerator::EnableLanguage(lang, mf);
+  this->cmGlobalGenerator::EnableLanguage(lang, mf, optional);
   this->GenerateConfigurations(mf);
   
   // if this environment variable is set, then copy it to

Source/cmGlobalVisualStudio7Generator.h

@@ -50,7 +50,7 @@ public:
    * extension, pthreads, byte order etc.  
    */
   virtual void EnableLanguage(std::vector<std::string>const& languages, 
-                              cmMakefile *);
+                              cmMakefile *, bool optional);
 
   /**
    * Try running cmake and building a file. This is used for dynalically

Source/cmGlobalVisualStudio8Win64Generator.cxx

@@ -49,8 +49,8 @@ void cmGlobalVisualStudio8Win64Generator
 
 void cmGlobalVisualStudio8Win64Generator
 ::EnableLanguage(std::vector<std::string>const &  lang, 
-                 cmMakefile *mf)
+                 cmMakefile *mf, bool optional)
 {
   mf->AddDefinition("CMAKE_FORCE_WIN64", "TRUE");
-  cmGlobalVisualStudio8Generator::EnableLanguage(lang, mf);
+  cmGlobalVisualStudio8Generator::EnableLanguage(lang, mf, optional);
 }

Source/cmGlobalVisualStudio8Win64Generator.h

@@ -49,6 +49,6 @@ public:
    * extension, pthreads, byte order etc.  
    */
   virtual void EnableLanguage(std::vector<std::string>const& languages, 
-                              cmMakefile *);
+                              cmMakefile *, bool optional);
 };
 #endif

Source/cmGlobalWatcomWMakeGenerator.cxx

@@ -28,7 +28,9 @@ cmGlobalWatcomWMakeGenerator::cmGlobalWatcomWMakeGenerator()
 }
 
 void cmGlobalWatcomWMakeGenerator
-::EnableLanguage(std::vector<std::string>const& l, cmMakefile *mf)
+::EnableLanguage(std::vector<std::string>const& l, 
+                 cmMakefile *mf, 
+                 bool optional)
 {
   // pick a default 
   mf->AddDefinition("WATCOM", "1");
@@ -39,7 +41,7 @@ void cmGlobalWatcomWMakeGenerator
   mf->AddDefinition("CMAKE_NO_QUOTED_OBJECTS", "1");
   mf->AddDefinition("CMAKE_GENERATOR_CC", "wcl386");
   mf->AddDefinition("CMAKE_GENERATOR_CXX", "wcl386");
-  this->cmGlobalUnixMakefileGenerator3::EnableLanguage(l, mf);
+  this->cmGlobalUnixMakefileGenerator3::EnableLanguage(l, mf, optional);
 }
 
 ///! Create a local generator appropriate to this Global Generator

Source/cmGlobalWatcomWMakeGenerator.h

@@ -45,7 +45,7 @@ public:
    * extension, pthreads, byte order etc.  
    */
   virtual void EnableLanguage(std::vector<std::string>const& languages, 
-                              cmMakefile *);
+                              cmMakefile *, bool optional);
 };
 
 #endif

Source/cmGlobalXCodeGenerator.cxx

@@ -104,7 +104,7 @@ cmGlobalGenerator* cmGlobalXCodeGenerator::New()
 //----------------------------------------------------------------------------
 void cmGlobalXCodeGenerator::EnableLanguage(std::vector<std::string>const&
                                             lang,
-                                            cmMakefile * mf)
+                                            cmMakefile * mf, bool optional)
 { 
   mf->AddDefinition("XCODE","1");
   if(this->XcodeVersion == 15)
@@ -125,7 +125,7 @@ void cmGlobalXCodeGenerator::EnableLanguage(std::vector<std::string>const&
   mf->AddDefinition("CMAKE_GENERATOR_NO_COMPILER_ENV", "1");
   // initialize Architectures so it can be used by 
   //  GetTargetObjectFileDirectories
-  this->cmGlobalGenerator::EnableLanguage(lang, mf);
+  this->cmGlobalGenerator::EnableLanguage(lang, mf, optional);
     const char* osxArch = 
       mf->GetDefinition("CMAKE_OSX_ARCHITECTURES");
   const char* sysroot = 

Source/cmGlobalXCodeGenerator.h

@@ -53,7 +53,7 @@ public:
    * extension, pthreads, byte order etc.  
    */
   virtual void EnableLanguage(std::vector<std::string>const& languages, 
-                              cmMakefile *);
+                              cmMakefile *, bool optional);
   /**
    * Try running cmake and building a file. This is used for dynalically
    * loaded commands, not as part of the usual build process.

Source/cmLocalVisualStudio6Generator.cxx

@@ -1044,7 +1044,7 @@ void cmLocalVisualStudio6Generator
       // Compute the proper name to use to link this library.
       std::string lib;
       std::string libDebug;
-      cmTarget* tgt = this->GlobalGenerator->FindTarget(0, j->first.c_str(), 
+      cmTarget* tgt = this->GlobalGenerator->FindTarget(0, j->first.c_str(),
                                                         false);
       if(tgt)
         {

Source/cmMakefile.cxx

@@ -2150,11 +2150,13 @@ cmSourceFile* cmMakefile::GetOrCreateSource(const char* sourceName,
     }
 }
 
-void cmMakefile::EnableLanguage(std::vector<std::string> const &  lang)
+void cmMakefile::EnableLanguage(std::vector<std::string> const &  lang, 
+                               bool optional)
 {
   this->AddDefinition("CMAKE_CFG_INTDIR",
-    this->LocalGenerator->GetGlobalGenerator()->GetCMakeCFGInitDirectory());
-  this->LocalGenerator->GetGlobalGenerator()->EnableLanguage(lang, this);
+  this->LocalGenerator->GetGlobalGenerator()->GetCMakeCFGInitDirectory());
+  this->LocalGenerator->GetGlobalGenerator()->EnableLanguage(lang, this, 
+                                                             optional);
 }
 
 void cmMakefile::ExpandSourceListArguments(

Source/cmMakefile.h

@@ -633,7 +633,7 @@ public:
 
   ///! Enable support for named language, if nil then all languages are
   ///enabled.
-  void EnableLanguage(std::vector<std::string>const& languages);
+  void EnableLanguage(std::vector<std::string>const& languages, bool optional);
 
   /**
    * Set/Get the name of the parent directories CMakeLists file

Source/cmProjectCommand.cxx

@@ -72,7 +72,7 @@ bool cmProjectCommand::InitialPass(std::vector<std::string> const& args)
     languages.push_back("C");
     languages.push_back("CXX");
     }
-  this->Makefile->EnableLanguage(languages);
+  this->Makefile->EnableLanguage(languages, false);
   return true;
 }