CPack allow RPM and DEB generator to be used on OSX.

More generally add the check for possible generator "activation" at
runtime depending on a generator specific check.
The dynamic behavior is currently implemented only for MacOS
and should be fully backward compatible for other system.

Inspired-By Tom Hughes <tomtheengineer@gmail.com>

Source/CPack/cmCPackDebGenerator.h

@@ -31,6 +31,17 @@ public:
   cmCPackDebGenerator();
   virtual ~cmCPackDebGenerator();
 
+  static bool CanGenerate()
+    {
+#ifdef __APPLE__
+    // on MacOS enable CPackDeb iff dpkg is found
+    return cmSystemTools::FindProgram("dpkg") != "" ? true : false;
+#else
+    // legacy behavior on other systems
+    return true;
+#endif
+    }
+
 protected:
   virtual int InitializeInternal();
   /**

Source/CPack/cmCPackGenerator.h

@@ -62,6 +62,16 @@ public:
     { this->GeneratorVerbose = val ?
       cmSystemTools::OUTPUT_MERGE : cmSystemTools::OUTPUT_NONE; }
 
+  /**
+   * Returns true if the generator may work on this system.
+   * Rational:
+   * Some CPack generator may run on some host and may not on others
+   * (with the same system) because some tools are missing. If the tool
+   * is missing then CPack won't activate (in the CPackGeneratorFactory)
+   * this particular generator.
+   */
+  static bool CanGenerate() { return true; }
+
   /**
    * Do the actual whole package processing.
    * Subclass may redefine it but its usually enough

Source/CPack/cmCPackGeneratorFactory.cxx

@@ -31,7 +31,7 @@
 #  include "cmCPackCygwinSourceGenerator.h"
 #endif
 
-#if !defined(_WIN32) && !defined(__APPLE__) \
+#if !defined(_WIN32) \
  && !defined(__QNXNTO__) && !defined(__BEOS__)
 #  include "cmCPackDebGenerator.h"
 #  include "cmCPackRPMGenerator.h"
@@ -43,41 +43,83 @@
 //----------------------------------------------------------------------
 cmCPackGeneratorFactory::cmCPackGeneratorFactory()
 {
-  this->RegisterGenerator("TGZ", "Tar GZip compression",
-    cmCPackTGZGenerator::CreateGenerator);
-  this->RegisterGenerator("STGZ", "Self extracting Tar GZip compression",
-    cmCPackSTGZGenerator::CreateGenerator);
-  this->RegisterGenerator("NSIS", "Null Soft Installer",
-    cmCPackNSISGenerator::CreateGenerator);
+  if (cmCPackTGZGenerator::CanGenerate())
+    {
+    this->RegisterGenerator("TGZ", "Tar GZip compression",
+      cmCPackTGZGenerator::CreateGenerator);
+    }
+  if (cmCPackSTGZGenerator::CanGenerate())
+    {
+    this->RegisterGenerator("STGZ", "Self extracting Tar GZip compression",
+      cmCPackSTGZGenerator::CreateGenerator);
+    }
+  if (cmCPackNSISGenerator::CanGenerate())
+    {
+    this->RegisterGenerator("NSIS", "Null Soft Installer",
+      cmCPackNSISGenerator::CreateGenerator);
+    }
 #ifdef __CYGWIN__
-  this->RegisterGenerator("CygwinBinary", "Cygwin Binary Installer",
-                          cmCPackCygwinBinaryGenerator::CreateGenerator);
-  this->RegisterGenerator("CygwinSource", "Cygwin Source Installer",
-                          cmCPackCygwinSourceGenerator::CreateGenerator);
+  if (cmCPackCygwinBinaryGenerator::CanGenerate())
+    {
+    this->RegisterGenerator("CygwinBinary", "Cygwin Binary Installer",
+                            cmCPackCygwinBinaryGenerator::CreateGenerator);
+    }
+  if (cmCPackCygwinSourceGenerator::CanGenerate())
+    {
+    this->RegisterGenerator("CygwinSource", "Cygwin Source Installer",
+                            cmCPackCygwinSourceGenerator::CreateGenerator);
+    }
 #endif
 
-  this->RegisterGenerator("ZIP", "ZIP file format",
-    cmCPackZIPGenerator::CreateGenerator);
-  this->RegisterGenerator("TBZ2", "Tar BZip2 compression",
-    cmCPackTarBZip2Generator::CreateGenerator);
-  this->RegisterGenerator("TZ", "Tar Compress compression",
-    cmCPackTarCompressGenerator::CreateGenerator);
+  if (cmCPackZIPGenerator::CanGenerate())
+    {
+    this->RegisterGenerator("ZIP", "ZIP file format",
+      cmCPackZIPGenerator::CreateGenerator);
+    }
+  if (cmCPackTarBZip2Generator::CanGenerate())
+    {
+    this->RegisterGenerator("TBZ2", "Tar BZip2 compression",
+      cmCPackTarBZip2Generator::CreateGenerator);
+    }
+  if (cmCPackTarCompressGenerator::CanGenerate())
+    {
+    this->RegisterGenerator("TZ", "Tar Compress compression",
+      cmCPackTarCompressGenerator::CreateGenerator);
+    }
 #ifdef __APPLE__
-  this->RegisterGenerator("DragNDrop", "Mac OSX Drag And Drop",
-    cmCPackDragNDropGenerator::CreateGenerator);
-  this->RegisterGenerator("Bundle", "Mac OSX bundle",
-    cmCPackBundleGenerator::CreateGenerator);
-  this->RegisterGenerator("PackageMaker", "Mac OSX Package Maker installer",
-    cmCPackPackageMakerGenerator::CreateGenerator);
-  this->RegisterGenerator("OSXX11", "Mac OSX X11 bundle",
-    cmCPackOSXX11Generator::CreateGenerator);
+  if (cmCPackDragNDropGenerator::CanGenerate())
+    {
+    this->RegisterGenerator("DragNDrop", "Mac OSX Drag And Drop",
+      cmCPackDragNDropGenerator::CreateGenerator);
+    }
+  if (cmCPackBundleGenerator::CanGenerate())
+    {
+    this->RegisterGenerator("Bundle", "Mac OSX bundle",
+      cmCPackBundleGenerator::CreateGenerator);
+    }
+  if (cmCPackPackageMakerGenerator::CanGenerate())
+    {
+    this->RegisterGenerator("PackageMaker", "Mac OSX Package Maker installer",
+      cmCPackPackageMakerGenerator::CreateGenerator);
+    }
+  if (cmCPackOSXX11Generator::CanGenerate())
+    {
+    this->RegisterGenerator("OSXX11", "Mac OSX X11 bundle",
+      cmCPackOSXX11Generator::CreateGenerator);
+    }
 #endif
-#if !defined(_WIN32) && !defined(__APPLE__) \
+#if !defined(_WIN32) \
   && !defined(__QNXNTO__) && !defined(__BEOS__)
-  this->RegisterGenerator("DEB", "Debian packages",
-    cmCPackDebGenerator::CreateGenerator);
-  this->RegisterGenerator("RPM", "RPM packages",
-    cmCPackRPMGenerator::CreateGenerator);
+  if (cmCPackDebGenerator::CanGenerate())
+    {
+    this->RegisterGenerator("DEB", "Debian packages",
+      cmCPackDebGenerator::CreateGenerator);
+    }
+  if (cmCPackRPMGenerator::CanGenerate())
+    {
+    this->RegisterGenerator("RPM", "RPM packages",
+      cmCPackRPMGenerator::CreateGenerator);
+    }
 #endif
 }
 

Source/CPack/cmCPackRPMGenerator.h

@@ -35,6 +35,17 @@ public:
   cmCPackRPMGenerator();
   virtual ~cmCPackRPMGenerator();
 
+  static bool CanGenerate()
+    {
+#ifdef __APPLE__
+    // on MacOS enable CPackRPM iff rpmbuild is found
+    return cmSystemTools::FindProgram("rpmbuild") != "" ? true : false;
+#else
+    // legacy behavior on other systems
+    return true;
+#endif
+    }
+
 protected:
   virtual int InitializeInternal();
   virtual int PackageFiles();