Allow generator expressions in LINK_INTERFACE_LIBRARIES.

The Config and IMPORTED_ variants may also contain generator
expressions.

If 'the implementation is the interface', then the result of
evaluating the expressions at generate time is used to populate
the IMPORTED_LINK_INTERFACE_LIBRARIES property.

1) In the case of non-static libraries, this is fine because the
  user still has the option to populate the LINK_INTERFACE_LIBRARIES
  with generator expressions if that is what is wanted.

2) In the case of static libraries, this prevents a footgun,
  enforcing that the interface and the implementation are really
  the same.

  Otherwise, the LINK_LIBRARIES could contain a generator
  expression which is evaluated with a different context at build
  time, and when used as an imported target. That would mean that the
  result of evaluating the INTERFACE_LINK_LIBRARIES property for
  a static library would not necessarily be the 'link implementation'.

  For example:

    add_library(libone STATIC libone.cpp)
    add_library(libtwo STATIC libtwo.cpp)
    add_library(libthree STATIC libthree.cpp)

    target_link_libraries(libtwo
      $<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,STATIC_LIBRARY>:libone>)
    target_link_libraries(libthree libtwo)

  If the LINK_LIBRARIES content was simply copied to the
  IMPORTED_LINK_INTERFACE_LIBRARIES, then libthree links to libone, but
  executables linking to libthree will not link to libone.

3) As the 'implementation is the interface' concept is to be
  deprecated in the future anyway, this should be fine.

1 files changed, 38 insertions, 12 deletions

diff --git a/Source/cmTarget.cxx b/Source/cmTarget.cxx
index 2cfb1bfd55..9b50b8e527 100644
--- a/Source/cmTarget.cxx
+++ b/Source/cmTarget.cxx
@@ -4896,16 +4896,30 @@ void cmTarget::ComputeImportInfo(std::string const& desired_config,
   {
   std::string linkProp = "IMPORTED_LINK_INTERFACE_LIBRARIES";
   linkProp += suffix;
-  if(const char* config_libs = this->GetProperty(linkProp.c_str()))
+
+  const char *propertyLibs = this->GetProperty(linkProp.c_str());
+
+  if(!propertyLibs)
     {
-    cmSystemTools::ExpandListArgument(config_libs,
-                                      info.LinkInterface.Libraries);
+    linkProp = "IMPORTED_LINK_INTERFACE_LIBRARIES";
+    propertyLibs = this->GetProperty(linkProp.c_str());
     }
-  else if(const char* libs =
-          this->GetProperty("IMPORTED_LINK_INTERFACE_LIBRARIES"))
+  if(propertyLibs)
     {
-    cmSystemTools::ExpandListArgument(libs,
-                                      info.LinkInterface.Libraries);
+    cmListFileBacktrace lfbt;
+    cmGeneratorExpression ge(lfbt);
+
+    cmGeneratorExpressionDAGChecker dagChecker(lfbt,
+                                        this->GetName(),
+                                        linkProp, 0, 0);
+    cmSystemTools::ExpandListArgument(ge.Parse(propertyLibs)
+                                       ->Evaluate(this->Makefile,
+                                                  desired_config.c_str(),
+                                                  false,
+                                                  headTarget,
+                                                  this,
+                                                  &dagChecker),
+                                    info.LinkInterface.Libraries);
     }
   }
 
@@ -5019,18 +5033,20 @@ bool cmTarget::ComputeLinkInterface(const char* config, LinkInterface& iface,
   // An explicit list of interface libraries may be set for shared
   // libraries and executables that export symbols.
   const char* explicitLibraries = 0;
+  std::string linkIfaceProp;
   if(this->GetType() == cmTarget::SHARED_LIBRARY ||
      this->IsExecutableWithExports())
     {
     // Lookup the per-configuration property.
-    std::string propName = "LINK_INTERFACE_LIBRARIES";
-    propName += suffix;
-    explicitLibraries = this->GetProperty(propName.c_str());
+    linkIfaceProp = "LINK_INTERFACE_LIBRARIES";
+    linkIfaceProp += suffix;
+    explicitLibraries = this->GetProperty(linkIfaceProp.c_str());
 
     // If not set, try the generic property.
     if(!explicitLibraries)
       {
-      explicitLibraries = this->GetProperty("LINK_INTERFACE_LIBRARIES");
+      linkIfaceProp = "LINK_INTERFACE_LIBRARIES";
+      explicitLibraries = this->GetProperty(linkIfaceProp.c_str());
       }
     }
 
@@ -5048,7 +5064,16 @@ bool cmTarget::ComputeLinkInterface(const char* config, LinkInterface& iface,
   if(explicitLibraries)
     {
     // The interface libraries have been explicitly set.
-    cmSystemTools::ExpandListArgument(explicitLibraries, iface.Libraries);
+    cmListFileBacktrace lfbt;
+    cmGeneratorExpression ge(lfbt);
+    cmGeneratorExpressionDAGChecker dagChecker(lfbt, this->GetName(),
+                                               linkIfaceProp, 0, 0);
+    cmSystemTools::ExpandListArgument(ge.Parse(explicitLibraries)->Evaluate(
+                                        this->Makefile,
+                                        config,
+                                        false,
+                                        headTarget,
+                                        this, &dagChecker), iface.Libraries);
 
     if(this->GetType() == cmTarget::SHARED_LIBRARY)
       {
@@ -5091,6 +5116,7 @@ bool cmTarget::ComputeLinkInterface(const char* config, LinkInterface& iface,
     // The link implementation is the default link interface.
     LinkImplementation const* impl = this->GetLinkImplementation(config,
                                                               headTarget);
+    iface.ImplementationIsInterface = true;
     iface.Libraries = impl->Libraries;
     iface.WrongConfigLibraries = impl->WrongConfigLibraries;
     if(this->GetType() == cmTarget::STATIC_LIBRARY)