ENH: CMAKE_<LANG>_LINKER_PREFERENCE is now an integer priority, not a

two-step priority (None or Prefered)
Current order: ASM 0, C 10, Fortran 20, CXX 30, Java 40
This is the same order as automake choses:
http://www.gnu.org/software/automake/manual/html_node/How-the-Linker-is-Chosen.html

This change should be backward compatible:
if there is a project using fortran and CXX, they had to set the
LINKER_LANGUAGE explicitely, otherwise cmake complained (but still generated
the project files). Explicitely setting the linker language still overrides
automatic detection.
If somebody has a custom language for cmake and the PREFERENCE starts with
"P", its changed to 100, which gives it preference over all other languages
(except the other custom languages which have also "Prefered"). "None" is
converted to 0.

Alex

3 files changed, 74 insertions, 56 deletions

diff --git a/Source/cmGlobalGenerator.cxx b/Source/cmGlobalGenerator.cxx
index cea5b2b..31adcf1 100644
--- a/Source/cmGlobalGenerator.cxx
+++ b/Source/cmGlobalGenerator.cxx
@@ -570,12 +570,35 @@ void cmGlobalGenerator::SetLanguageEnabledMaps(const char* l, cmMakefile* mf)
   std::string linkerPrefVar = std::string("CMAKE_") +
     std::string(l) + std::string("_LINKER_PREFERENCE");
   const char* linkerPref = mf->GetDefinition(linkerPrefVar.c_str());
-  if(!linkerPref)
+  int preference = 0;
+  if(linkerPref)
     {
-    linkerPref = "None";
+    if (sscanf(linkerPref, "%d", &preference)!=1)
+      {
+      // backward compatibility: before 2.6 LINKER_PREFERENCE
+      // was either "None" or "Prefered", and only the first character was 
+      // tested. So if there is a custom language out there and it is 
+      // "Prefered", set its preference high
+      if (linkerPref[0]=='P')
+        {
+        preference = 100;
+        }
+      else
+        {
+        preference = 0;
+        }
+      }
     }
-  this->LanguageToLinkerPreference[l] = linkerPref;
 
+  if (preference < 0)
+    {
+    std::string msg = linkerPrefVar;
+    msg += " is negative, adjusting it to 0";
+    cmSystemTools::Message(msg.c_str(), "Warning");
+    preference = 0;
+    }
+
+  this->LanguageToLinkerPreference[l] = preference;
 
   std::string outputExtensionVar = std::string("CMAKE_") +
     std::string(l) + std::string("_OUTPUT_EXTENSION");
@@ -752,10 +775,6 @@ void cmGlobalGenerator::Configure()
         }
       notFoundVars += "\n";
       }
-    cmSystemTools::Error("This project requires some variables to be set,\n"
-                         "and cmake can not find them.\n"
-                         "Please set the following variables:\n",
-                         notFoundVars.c_str());
     }
   // at this point this->LocalGenerators has been filled,
   // so create the map from project name to vector of local generators
@@ -1120,13 +1139,14 @@ void cmGlobalGenerator::GetEnabledLanguages(std::vector<std::string>& lang)
     }
 }
 
-const char* cmGlobalGenerator::GetLinkerPreference(const char* lang)
+int cmGlobalGenerator::GetLinkerPreference(const char* lang)
 {
-  if(this->LanguageToLinkerPreference.count(lang))
+  std::map<cmStdString, int>::const_iterator it = this->LanguageToLinkerPreference.find(lang);
+  if (it != this->LanguageToLinkerPreference.end())
     {
-    return this->LanguageToLinkerPreference[lang].c_str();
+    return it->second;
     }
-  return "None";
+  return 0;
 }
 
 void cmGlobalGenerator::FillProjectMap()
diff --git a/Source/cmGlobalGenerator.h b/Source/cmGlobalGenerator.h
index 959945c..ccf00d7 100644
--- a/Source/cmGlobalGenerator.h
+++ b/Source/cmGlobalGenerator.h
@@ -153,7 +153,7 @@ public:
   ///! is an extension to be ignored
   bool IgnoreFile(const char* ext);
   ///! What is the preference for linkers and this language (None or Prefered)
-  const char* GetLinkerPreference(const char* lang);
+  int GetLinkerPreference(const char* lang);
   ///! What is the object file extension for a given source file?
   const char* GetLanguageOutputExtension(cmSourceFile const&);
 
@@ -257,7 +257,7 @@ private:
   std::map<cmStdString, cmStdString> OutputExtensions;
   std::map<cmStdString, cmStdString> LanguageToOutputExtension;
   std::map<cmStdString, cmStdString> ExtensionToLanguage;
-  std::map<cmStdString, cmStdString> LanguageToLinkerPreference; 
+  std::map<cmStdString, int> LanguageToLinkerPreference; 
 
   // this is used to improve performance 
   std::map<cmStdString,cmTarget *> TotalTargets;
diff --git a/Source/cmTarget.cxx b/Source/cmTarget.cxx
index 70d0035..40132a5 100644
--- a/Source/cmTarget.cxx
+++ b/Source/cmTarget.cxx
@@ -1477,59 +1477,57 @@ const char* cmTarget::GetLinkerLanguage(cmGlobalGenerator* gg)
     const_cast<cmTarget*>(this)->SetProperty("LINKER_LANGUAGE", "CXX");
     }
   const char* linkerLang = this->GetProperty("LINKER_LANGUAGE");
-  if(linkerLang)
+  if (linkerLang==0)
     {
-    return linkerLang;
-    }
-  std::set<cmStdString> languages;
-  for(std::vector<cmSourceFile*>::const_iterator i
-        = this->SourceFiles.begin();
-      i != this->SourceFiles.end(); ++i)
-    {
-    if(const char* lang = (*i)->GetLanguage())
+    // if the property has not yet been set, collect all languages in the
+    // target and then find the language with the highest preference value
+    std::set<cmStdString> languages;
+    for(std::vector<cmSourceFile*>::const_iterator 
+        i = this->SourceFiles.begin(); i != this->SourceFiles.end(); ++i)
       {
-      languages.insert(lang);
+      if(const char* lang = (*i)->GetLanguage())
+        {
+        languages.insert(lang);
+        }
       }
-    }
-  if(languages.size() == 0)
-    {
-    return 0;
-    }
-  if(languages.size() == 1)
-    {
-    const_cast<cmTarget*>(this)->SetProperty("LINKER_LANGUAGE",
-                                             languages.begin()->c_str());
-    return this->GetProperty("LINKER_LANGUAGE");
-    }
-  const char* prefLang = 0;
-  for(std::set<cmStdString>::const_iterator s = languages.begin();
-      s != languages.end(); ++s)
-    {
-    const char* lpref = gg->GetLinkerPreference(s->c_str());
-    if(lpref[0] == 'P')
+
+    std::string linkerLangList;              // only used for the error message
+    int maxLinkerPref = 0;
+    bool multiplePreferedLanguages = false;
+    for(std::set<cmStdString>::const_iterator sit = languages.begin();
+        sit != languages.end(); ++sit)
       {
-      if(prefLang && !(*s == prefLang))
+      int linkerPref = gg->GetLinkerPreference(sit->c_str());
+      if ((linkerPref > maxLinkerPref) || (linkerLang==0))
         {
-        std::string m = "Error Target: ";
-        m += this->Name + " Contains more than one Prefered language: ";
-        m += *s;
-        m += " and ";
-        m += prefLang;
-        m += "\nYou must set the LINKER_LANGUAGE property for this target.";
-        cmSystemTools::Error(m.c_str());
+        maxLinkerPref = linkerPref;
+        linkerLang = sit->c_str();
+        linkerLangList = *sit;
+        multiplePreferedLanguages = false;
         }
-      else
+      else if (linkerPref == maxLinkerPref)
         {
-        prefLang = s->c_str();
+        linkerLangList += "; ";
+        linkerLangList += *sit;
+        multiplePreferedLanguages = true;
         }
       }
+
+    if (linkerLang!=0)
+      {
+      const_cast<cmTarget*>(this)->SetProperty("LINKER_LANGUAGE", linkerLang);
+      }
+    if (multiplePreferedLanguages)
+      {
+      cmOStringStream err;
+      err << "Error: Target " << this->Name << " contains multiple languages "
+          << "with the highest linker preference (" << maxLinkerPref << "): " 
+          << linkerLangList << "\n"
+          << "You must set the LINKER_LANGUAGE property for this target.";
+      cmSystemTools::Error(err.str().c_str());
+      }
     }
-  if(!prefLang)
-    {
-    prefLang = languages.begin()->c_str();
-    }
-  const_cast<cmTarget*>(this)->SetProperty("LINKER_LANGUAGE", prefLang);
-  return this->GetProperty("LINKER_LANGUAGE");
+  return linkerLang;
 }
 
 //----------------------------------------------------------------------------