Create make rules for INTERFACE_LIBRARY targets.

The result is that the depends of the target are created.

So,

 add_library(somelib foo.cpp)
 add_library(anotherlib EXCLUDE_FROM_ALL foo.cpp)
 add_library(extra EXCLUDE_FROM_ALL foo.cpp)
 target_link_libraries(anotherlib extra)

 add_library(iface INTERFACE)
 target_link_libraries(iface INTERFACE anotherlib)

Executing 'make iface' will result in the anotherlib and extra targets
being made.

Adding a regular executable to the INTERFACE of an INTERFACE_LIBRARY
will not result in the executable being built with 'make iface' because
of the logic in cmComputeTargetDepends::AddTargetDepend.

So far, this is implemented only for the Makefile generator. Other
generators will follow if this feature is possible for them.

Make INTERFACE_LIBRARY targets part of the all target by default.
Test this by building the all target and making the expected library
EXCLUDE_FROM_ALL.

Source/cmComputeTargetDepends.cxx

@@ -208,7 +208,15 @@ void cmComputeTargetDepends::CollectTargetDepends(int depender_index)
   std::set<cmStdString> emitted;
   {
   std::vector<std::string> tlibs;
+  if (depender->GetType() == cmTarget::INTERFACE_LIBRARY)
+    {
+    // For INTERFACE_LIBRARY depend on the interface instead.
+    depender->GetInterfaceLinkLibraries(0, tlibs, depender);
+    }
+  else
+    {
     depender->GetDirectLinkLibraries(0, tlibs, depender);
+    }
   // A target should not depend on itself.
   emitted.insert(depender->GetName());
   for(std::vector<std::string>::const_iterator lib = tlibs.begin();

Source/cmGlobalUnixMakefileGenerator3.cxx

@@ -435,6 +435,7 @@ cmGlobalUnixMakefileGenerator3
        (l->second.GetType() == cmTarget::SHARED_LIBRARY) ||
        (l->second.GetType() == cmTarget::MODULE_LIBRARY) ||
        (l->second.GetType() == cmTarget::OBJECT_LIBRARY) ||
+       (l->second.GetType() == cmTarget::INTERFACE_LIBRARY) ||
        (l->second.GetType() == cmTarget::UTILITY))
       {
       // Add this to the list of depends rules in this directory.
@@ -612,6 +613,7 @@ cmGlobalUnixMakefileGenerator3
           (t->second.GetType() == cmTarget::SHARED_LIBRARY) ||
           (t->second.GetType() == cmTarget::MODULE_LIBRARY) ||
           (t->second.GetType() == cmTarget::OBJECT_LIBRARY) ||
+          (t->second.GetType() == cmTarget::INTERFACE_LIBRARY) ||
           (t->second.GetType() == cmTarget::UTILITY)))
         {
         // Add a rule to build the target by name.
@@ -633,6 +635,10 @@ cmGlobalUnixMakefileGenerator3
                           t->second.GetName(), depends, commands,
                           true);
 
+        if (t->second.GetType() == cmTarget::INTERFACE_LIBRARY)
+          {
+          continue;
+          }
         // Add a fast rule to build the target
         std::string localName = lg->GetRelativeTargetDirectory(t->second);
         std::string makefileName;
@@ -699,6 +705,7 @@ cmGlobalUnixMakefileGenerator3
         || (t->second.GetType() == cmTarget::SHARED_LIBRARY)
         || (t->second.GetType() == cmTarget::MODULE_LIBRARY)
         || (t->second.GetType() == cmTarget::OBJECT_LIBRARY)
+        || (t->second.GetType() == cmTarget::INTERFACE_LIBRARY)
         || (t->second.GetType() == cmTarget::UTILITY)))
       {
       std::string makefileName;
@@ -715,6 +722,9 @@ cmGlobalUnixMakefileGenerator3
         << localName << "\n\n";
 
       commands.clear();
+
+      if(t->second.GetType() != cmTarget::INTERFACE_LIBRARY)
+        {
         makeTargetName = localName;
         makeTargetName += "/depend";
         commands.push_back(lg->GetRecursiveMakeCall
@@ -760,8 +770,16 @@ cmGlobalUnixMakefileGenerator3
         progressDir = "Built target ";
         progressDir += t->first;
         lg->AppendEcho(commands,progressDir.c_str());
-
+        }
+      else
+        {
+        depends.clear();
+        }
       this->AppendGlobalTargetDepends(depends,t->second);
+      if(depends.empty() && this->EmptyRuleHackDepends != "")
+        {
+        depends.push_back(this->EmptyRuleHackDepends);
+        }
       lg->WriteMakeRule(ruleFileStream, "All Build rule for target.",
                         localName.c_str(), depends, commands, true);
 
@@ -777,7 +795,7 @@ cmGlobalUnixMakefileGenerator3
 
       // Write the rule.
       commands.clear();
-      progressDir = lg->GetMakefile()->GetHomeOutputDirectory();
+      std::string progressDir = lg->GetMakefile()->GetHomeOutputDirectory();
       progressDir += cmake::GetCMakeFilesDirectory();
 
       {

Source/cmLocalUnixMakefileGenerator3.cxx

@@ -381,6 +381,7 @@ void cmLocalUnixMakefileGenerator3
        (t->second.GetType() == cmTarget::SHARED_LIBRARY) ||
        (t->second.GetType() == cmTarget::MODULE_LIBRARY) ||
        (t->second.GetType() == cmTarget::OBJECT_LIBRARY) ||
+       (t->second.GetType() == cmTarget::INTERFACE_LIBRARY) ||
        (t->second.GetType() == cmTarget::UTILITY))
       {
       emitted.insert(t->second.GetName());

Source/cmMakefileLibraryTargetGenerator.cxx

@@ -82,6 +82,9 @@ void cmMakefileLibraryTargetGenerator::WriteRuleFiles()
     case cmTarget::OBJECT_LIBRARY:
       this->WriteObjectLibraryRules();
       break;
+    case cmTarget::INTERFACE_LIBRARY:
+      // Nothing to do.
+      break;
     default:
       // If language is not known, this is an error.
       cmSystemTools::Error("Unknown Library Type");

Source/cmMakefileTargetGenerator.cxx

@@ -75,6 +75,7 @@ cmMakefileTargetGenerator::New(cmTarget *tgt)
     case cmTarget::SHARED_LIBRARY:
     case cmTarget::MODULE_LIBRARY:
     case cmTarget::OBJECT_LIBRARY:
+    case cmTarget::INTERFACE_LIBRARY:
       result = new cmMakefileLibraryTargetGenerator(tgt);
       break;
     case cmTarget::UTILITY:

Source/cmTarget.cxx

@@ -1111,6 +1111,29 @@ void cmTarget::GetDirectLinkLibraries(const char *config,
     }
 }
 
+//----------------------------------------------------------------------------
+void cmTarget::GetInterfaceLinkLibraries(const char *config,
+                            std::vector<std::string> &libs, cmTarget *head)
+{
+  const char *prop = this->GetProperty("INTERFACE_LINK_LIBRARIES");
+  if (prop)
+    {
+    cmListFileBacktrace lfbt;
+    cmGeneratorExpression ge(lfbt);
+    const cmsys::auto_ptr<cmCompiledGeneratorExpression> cge = ge.Parse(prop);
+
+    cmGeneratorExpressionDAGChecker dagChecker(lfbt,
+                                        this->GetName(),
+                                        "INTERFACE_LINK_LIBRARIES", 0, 0);
+    cmSystemTools::ExpandListArgument(cge->Evaluate(this->Makefile,
+                                        config,
+                                        false,
+                                        head,
+                                        &dagChecker),
+                                      libs);
+    }
+}
+
 //----------------------------------------------------------------------------
 std::string cmTarget::GetDebugGeneratorExpressions(const std::string &value,
                                   cmTarget::LinkLibraryType llt)

Source/cmTarget.h

@@ -177,6 +177,9 @@ public:
   void GetDirectLinkLibraries(const char *config,
                               std::vector<std::string> &,
                               cmTarget *head);
+  void GetInterfaceLinkLibraries(const char *config,
+                              std::vector<std::string> &,
+                              cmTarget *head);
 
   /** Compute the link type to use for the given configuration.  */
   LinkLibraryType ComputeLinkType(const char* config);

Tests/CMakeLists.txt

@@ -261,6 +261,23 @@ if(BUILD_TESTING)
       PASS_REGULAR_EXPRESSION "(file is not of required architecture|does not match cputype|not the architecture being linked)")
   endif()
 
+  if(CMAKE_TEST_GENERATOR MATCHES Make)
+    set(InterfaceBuildTargets_libname testlib)
+    if (CMAKE_TEST_GENERATOR MATCHES "Borland|Watcom")
+      set(InterfaceBuildTargets_libname testlib.lib)
+    endif()
+    add_test(InterfaceBuildTargets ${CMAKE_CTEST_COMMAND}
+      --build-and-test
+      "${CMake_SOURCE_DIR}/Tests/InterfaceBuildTargets"
+      "${CMake_BINARY_DIR}/Tests/InterfaceBuildTargets"
+      --build-two-config
+      ${build_generator_args}
+      --build-project InterfaceBuildTargets
+      --test-command ${CMAKE_CMAKE_COMMAND} -E touch_nocreate ${InterfaceBuildTargets_libname}
+      )
+    list(APPEND TEST_BUILD_DIRS "${CMake_BINARY_DIR}/Tests/InterfaceBuildTargets")
+  endif()
+
   list(APPEND TEST_BUILD_DIRS ${CMake_TEST_INSTALL_PREFIX})
 
   if(NOT QT4_FOUND)

Tests/InterfaceBuildTargets/CMakeLists.txt

@@ -0,0 +1,13 @@
+project(InterfaceBuildTargets)
+
+add_library(testlib EXCLUDE_FROM_ALL testlib.cxx)
+set_property(TARGET testlib PROPERTY PREFIX "")
+if(CMAKE_GENERATOR MATCHES "Borland|Watcom")
+  # These librarians add the .lib suffix anyway.
+  set_property(TARGET testlib PROPERTY SUFFIX ".lib")
+else()
+  set_property(TARGET testlib PROPERTY SUFFIX "")
+endif()
+
+add_library(iface INTERFACE)
+target_link_libraries(iface INTERFACE testlib)

Tests/InterfaceBuildTargets/main.cxx

@@ -0,0 +1,5 @@
+
+int main(int, char**)
+{
+  return 0;
+}

Tests/InterfaceBuildTargets/testlib.cxx

@@ -0,0 +1,5 @@
+
+void testlib(void)
+{
+
+}