Don't add invalid content to static lib INTERFACE_LINK_LIBRARIES.

Only valid target names or generator expressions may appear in
the target field of a LINK_ONLY expression.

Other content like link flags should still be added to that property
(wrapped in config-specific generator expressions), but not wrapped
in LINK_ONLY. Otherwise undue warnings would be issued for the
policy CMP0022.

The LINK_ONLY expression only has an effect for actual target
names anyway, so there is no logical deficit.

Source/cmTarget.cxx

@@ -2331,15 +2331,20 @@ void cmTarget::MergeLinkLibraries( cmMakefile& mf,
   i += this->PrevLinkedLibraries.size();
   for( ; i != libs.end(); ++i )
     {
+    const char *lib = i->first.c_str();
     // We call this so that the dependencies get written to the cache
-    this->AddLinkLibrary( mf, selfname, i->first.c_str(), i->second );
+    this->AddLinkLibrary( mf, selfname, lib, i->second );
 
     if (this->GetType() == cmTarget::STATIC_LIBRARY)
       {
-      this->AppendProperty("INTERFACE_LINK_LIBRARIES",
-            ("$<LINK_ONLY:" +
-            this->GetDebugGeneratorExpressions(i->first.c_str(), i->second) +
-            ">").c_str());
+      std::string configLib = this->GetDebugGeneratorExpressions(lib,
+                                                                 i->second);
+      if (cmGeneratorExpression::IsValidTargetName(lib)
+          || cmGeneratorExpression::Find(lib) != std::string::npos)
+        {
+        configLib = "$<LINK_ONLY:" + configLib + ">";
+        }
+        this->AppendProperty("INTERFACE_LINK_LIBRARIES", configLib.c_str());
       }
     }
   this->PrevLinkedLibraries = libs;

Source/cmTargetLinkLibrariesCommand.cxx

@@ -384,10 +384,15 @@ cmTargetLinkLibrariesCommand::HandleLibrary(const char* lib,
       {
       if (this->Target->GetType() == cmTarget::STATIC_LIBRARY)
         {
+        std::string configLib = this->Target
+                                     ->GetDebugGeneratorExpressions(lib, llt);
+        if (cmGeneratorExpression::IsValidTargetName(lib)
+            || cmGeneratorExpression::Find(lib) != std::string::npos)
+          {
+          configLib = "$<LINK_ONLY:" + configLib + ">";
+          }
         this->Target->AppendProperty("INTERFACE_LINK_LIBRARIES",
-                  ("$<LINK_ONLY:" +
-                  this->Target->GetDebugGeneratorExpressions(lib, llt) +
-                  ">").c_str());
+                                     configLib.c_str());
         }
       // Not a 'public' or 'interface' library. Do not add to interface
       // property.

Tests/CMakeCommands/target_link_libraries/cmp0022/CMakeLists.txt

@@ -22,6 +22,9 @@ generate_export_header(staticlib1)
 add_library(staticlib2 STATIC staticlib2.cpp)
 generate_export_header(staticlib2)
 target_link_libraries(staticlib1 LINK_PUBLIC staticlib2)
+if (CMAKE_CXX_COMPILER_ID MATCHES GNU OR CMAKE_CXX_COMPILER_ID MATCHES Clang)
+  target_link_libraries(staticlib1 LINK_PRIVATE "-Wl,-v")
+endif()
 
 add_executable(staticlib_exe staticlib_exe.cpp)
 target_link_libraries(staticlib_exe staticlib1)

Tests/RunCMake/CMP0022/CMP0022-NOWARN-static.cmake

@@ -5,4 +5,8 @@ add_library(foo STATIC empty_vs6_1.cpp)
 add_library(bar STATIC empty_vs6_2.cpp)
 add_library(bat STATIC empty_vs6_3.cpp)
 target_link_libraries(foo bar)
-target_link_libraries(bar bat)
+# The last element here needs to contain a space so that it is a single
+# element which is not a valid target name. As bar is a STATIC library,
+# this tests that the LINK_ONLY generator expression is not used for
+# that element, creating an error.
+target_link_libraries(bar bat "-lz -lm")