CMP0065: Restrict the use of CMAKE_SHARED_LIBRARY_LINK_<LANG>_FLAGS

This new policy restricts the addition of the shared library link flags
to executables only when the ENABLE_EXPORTS property is set to True.

Help/manual/cmake-policies.7.rst

@@ -122,3 +122,4 @@ All Policies
    /policy/CMP0062
    /policy/CMP0063
    /policy/CMP0064
+   /policy/CMP0065

Help/manual/cmake-variables.7.rst

@@ -245,6 +245,7 @@ Variables that Control the Build
    /variable/CMAKE_COMPILE_PDB_OUTPUT_DIRECTORY_CONFIG
    /variable/CMAKE_CONFIG_POSTFIX
    /variable/CMAKE_DEBUG_POSTFIX
+   /variable/CMAKE_ENABLE_EXPORTS
    /variable/CMAKE_EXE_LINKER_FLAGS_CONFIG
    /variable/CMAKE_EXE_LINKER_FLAGS
    /variable/CMAKE_Fortran_FORMAT

Help/policy/CMP0065.rst

@@ -0,0 +1,27 @@
+CMP0065
+-------
+
+Do not add flags to export symbols from executables without
+the :prop_tgt:`ENABLE_EXPORTS` target property.
+
+CMake 3.3 and below, for historical reasons, always linked executables
+on some platforms with flags like ``-rdynamic`` to export symbols from
+the executables for use by any plugins they may load via ``dlopen``.
+CMake 3.4 and above prefer to do this only for executables that are
+explicitly marked with the :prop_tgt:`ENABLE_EXPORTS` target property.
+
+The ``OLD`` behavior of this policy is to always use the additional link
+flags when linking executables regardless of the value of the
+:prop_tgt:`ENABLE_EXPORTS` target property.
+
+The ``NEW`` behavior of this policy is to only use the additional link
+flags when linking executables if the :prop_tgt:`ENABLE_EXPORTS` target
+property is set to ``True``.
+
+This policy was introduced in CMake version 3.4.  Unlike most policies,
+CMake version |release| does *not* warn by default when this policy
+is not set and simply uses OLD behavior.  See documentation of the
+:variable:`CMAKE_POLICY_WARNING_CMP0065 <CMAKE_POLICY_WARNING_CMP<NNNN>>`
+variable to control the warning.
+
+.. include:: DEPRECATED.txt

Help/prop_tgt/ENABLE_EXPORTS.rst

@@ -7,7 +7,7 @@ Normally an executable does not export any symbols because it is the
 final program.  It is possible for an executable to export symbols to
 be used by loadable modules.  When this property is set to true CMake
 will allow other targets to "link" to the executable with the
-TARGET_LINK_LIBRARIES command.  On all platforms a target-level
+:command:`TARGET_LINK_LIBRARIES` command.  On all platforms a target-level
 dependency on the executable is created for targets that link to it.
 For DLL platforms an import library will be created for the exported
 symbols and then used for linking.  All Windows-based systems
@@ -17,3 +17,6 @@ module will "link" to the executable using a flag like
 "-bundle_loader".  For other non-DLL platforms the link rule is simply
 ignored since the dynamic loader will automatically bind symbols when
 the module is loaded.
+
+This property is initialized by the value of the variable
+:variable:`CMAKE_ENABLE_EXPORTS` if it is set when a target is created.

Help/release/dev/restrict-shlib-link-flags-to-enable-exports.rst

@@ -0,0 +1,6 @@
+restrict-shlib-link-flags-to-enable-exports
+-------------------------------------------
+
+* CMake no longer links executables with flags to export symbols
+  unless the :prop_tgt:`ENABLE_EXPORTS` target property is set.
+  See policy :policy:`CMP0065`.

Help/variable/CMAKE_ENABLE_EXPORTS.rst

@@ -0,0 +1,22 @@
+CMAKE_ENABLE_EXPORTS
+--------------------
+
+Specify whether an executable exports symbols for loadable modules.
+
+Normally an executable does not export any symbols because it is the
+final program.  It is possible for an executable to export symbols to
+be used by loadable modules.  When this property is set to true CMake
+will allow other targets to "link" to the executable with the
+:command:`TARGET_LINK_LIBRARIES` command.  On all platforms a target-level
+dependency on the executable is created for targets that link to it.
+For DLL platforms an import library will be created for the exported
+symbols and then used for linking.  All Windows-based systems
+including Cygwin are DLL platforms.  For non-DLL platforms that
+require all symbols to be resolved at link time, such as Mac OS X, the
+module will "link" to the executable using a flag like
+"-bundle_loader".  For other non-DLL platforms the link rule is simply
+ignored since the dynamic loader will automatically bind symbols when
+the module is loaded.
+
+This variable is used to initialize the target property
+:prop_tgt:`ENABLE_EXPORTS` for executable targets.

Help/variable/CMAKE_POLICY_WARNING_CMPNNNN.rst

@@ -13,6 +13,8 @@ warn by default:
   policy :policy:`CMP0056`.
 * ``CMAKE_POLICY_WARNING_CMP0060`` controls the warning for
   policy :policy:`CMP0060`.
+* ``CMAKE_POLICY_WARNING_CMP0065`` controls the warning for
+  policy :policy:`CMP0065`.
 
 This variable should not be set by a project in CMake code.  Project
 developers running CMake may set this variable in their cache to

Source/cmLocalGenerator.cxx

@@ -1540,13 +1540,47 @@ void cmLocalGenerator::OutputLinkLibraries(std::string& linkLibraries,
     this->Makefile->GetSafeDefinition("CMAKE_LIBRARY_PATH_TERMINATOR");
 
   // Flags to link an executable to shared libraries.
-  std::string linkFlagsVar = "CMAKE_SHARED_LIBRARY_LINK_";
-  linkFlagsVar += linkLanguage;
-  linkFlagsVar += "_FLAGS";
   if( tgt.GetType() == cmTarget::EXECUTABLE )
     {
-    linkLibs = this->Makefile->GetSafeDefinition(linkFlagsVar);
-    linkLibs += " ";
+    bool add_shlib_flags = false;
+    switch(tgt.Target->GetPolicyStatusCMP0065())
+      {
+      case cmPolicies::WARN:
+        if(!tgt.GetPropertyAsBool("ENABLE_EXPORTS") &&
+           this->Makefile->PolicyOptionalWarningEnabled(
+             "CMAKE_POLICY_WARNING_CMP0065"))
+          {
+          std::ostringstream w;
+          w << cmPolicies::GetPolicyWarning(cmPolicies::CMP0065) << "\n"
+            "For compatibility with older versions of CMake, "
+            "additional flags may be added to export symbols on all "
+            "executables regardless of thier ENABLE_EXPORTS property.";
+          this->Makefile->IssueMessage(cmake::AUTHOR_WARNING, w.str());
+          }
+      case cmPolicies::OLD:
+        // OLD behavior is to always add the flags
+        add_shlib_flags = true;
+        break;
+      case cmPolicies::REQUIRED_IF_USED:
+      case cmPolicies::REQUIRED_ALWAYS:
+        this->Makefile->IssueMessage(
+          cmake::FATAL_ERROR,
+          cmPolicies::GetRequiredPolicyError(cmPolicies::CMP0065)
+          );
+      case cmPolicies::NEW:
+        // NEW behavior is to only add the flags if ENABLE_EXPORTS is on
+        add_shlib_flags = tgt.GetPropertyAsBool("ENABLE_EXPORTS");
+        break;
+      }
+
+    if(add_shlib_flags)
+      {
+      std::string linkFlagsVar = "CMAKE_SHARED_LIBRARY_LINK_";
+      linkFlagsVar += linkLanguage;
+      linkFlagsVar += "_FLAGS";
+      linkLibs = this->Makefile->GetSafeDefinition(linkFlagsVar);
+      linkLibs += " ";
+      }
     }
 
   // Append the framework search path flags.

Source/cmPolicies.h

@@ -220,6 +220,10 @@ class cmPolicy;
     3, 3, 0, cmPolicies::WARN) \
   SELECT(POLICY, CMP0064, \
     "Support new TEST if() operator.", \
+    3, 4, 0, cmPolicies::WARN) \
+  SELECT(POLICY, CMP0065, \
+    "Do not add flags to export symbols from executables without " \
+    "the ENABLE_EXPORTS target property.", \
     3, 4, 0, cmPolicies::WARN)
 
 #define CM_SELECT_ID(F, A1, A2, A3, A4, A5, A6) F(A1)

Source/cmTarget.cxx

@@ -347,6 +347,7 @@ void cmTarget::SetMakefile(cmMakefile* mf)
     {
     this->SetPropertyDefault("ANDROID_GUI", 0);
     this->SetPropertyDefault("CROSSCOMPILING_EMULATOR", 0);
+    this->SetPropertyDefault("ENABLE_EXPORTS", 0);
     }
   if(this->TargetTypeValue == cmTarget::SHARED_LIBRARY
       || this->TargetTypeValue == cmTarget::MODULE_LIBRARY)

Source/cmTarget.h

@@ -41,7 +41,8 @@
   F(CMP0046) \
   F(CMP0052) \
   F(CMP0060) \
-  F(CMP0063)
+  F(CMP0063) \
+  F(CMP0065)
 
 class cmake;
 class cmMakefile;

Tests/RunCMake/CMP0065/BuildTargetInSubProject.cmake

@@ -0,0 +1,15 @@
+function(BuildTargetInSubProject P T E)
+  try_compile(RESULTVAR
+    ${CMAKE_CURRENT_BINARY_DIR}/subproject
+    ${CMAKE_CURRENT_SOURCE_DIR}/subproject
+    ${P} ${T} OUTPUT_VARIABLE O)
+  if(E AND RESULTVAR)
+    message(STATUS "${P} target ${T} succeeded as expected")
+  elseif(E AND NOT RESULTVAR)
+    message(FATAL_ERROR "${P} target ${T} failed but should have succeeded.  Output:${O}")
+  elseif(NOT E AND NOT RESULTVAR)
+    message(STATUS "${P} target ${T} failed as expected")
+  elseif(NOT E AND RESULTVAR)
+    message(FATAL_ERROR "${P} target ${T} succeeded but should have failed.  Output:${O}")
+  endif()
+endfunction()

Tests/RunCMake/CMP0065/CMakeLists.txt

@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 3.3)
+project(${RunCMake_TEST} NONE)
+include(${RunCMake_TEST}.cmake)

Tests/RunCMake/CMP0065/NEWBad.cmake

@@ -0,0 +1,4 @@
+enable_language(C)
+include(BuildTargetInSubProject.cmake)
+
+BuildTargetInSubProject(TestPolicyCMP0065 FooNEWBad FALSE)

Tests/RunCMake/CMP0065/NEWGood.cmake

@@ -0,0 +1,4 @@
+enable_language(C)
+include(BuildTargetInSubProject.cmake)
+
+BuildTargetInSubProject(TestPolicyCMP0065 FooNEWGood TRUE)

Tests/RunCMake/CMP0065/OLDBad1.cmake

@@ -0,0 +1,4 @@
+enable_language(C)
+include(BuildTargetInSubProject.cmake)
+
+BuildTargetInSubProject(TestPolicyCMP0065 FooOLDBad1 FALSE)

Tests/RunCMake/CMP0065/OLDBad2.cmake

@@ -0,0 +1,4 @@
+enable_language(C)
+include(BuildTargetInSubProject.cmake)
+
+BuildTargetInSubProject(TestPolicyCMP0065 FooOLDBad2 FALSE)

Tests/RunCMake/CMP0065/RunCMakeTest.cmake

@@ -0,0 +1,8 @@
+include(RunCMake)
+
+run_cmake(OLDBad1)
+run_cmake(OLDBad2)
+run_cmake(NEWBad)
+run_cmake(NEWGood)
+run_cmake(WARN-OFF)
+run_cmake(WARN-ON)

Tests/RunCMake/CMP0065/WARN-OFF.cmake

@@ -0,0 +1,3 @@
+
+enable_language(C)
+add_executable(main subproject/main.c)

Tests/RunCMake/CMP0065/WARN-ON-stderr.txt

@@ -0,0 +1,10 @@
+CMake Warning \(dev\) in CMakeLists.txt:
+  Policy CMP0065 is not set: Do not add flags to export symbols from
+  executables without the ENABLE_EXPORTS target property.  Run "cmake
+  --help-policy CMP0065" for policy details.  Use the cmake_policy command to
+  set the policy and suppress this warning.
+
+  For compatibility with older versions of CMake, additional flags may be
+  added to export symbols on all executables regardless of thier
+  ENABLE_EXPORTS property.
+This warning is for project developers.  Use -Wno-dev to suppress it.

Tests/RunCMake/CMP0065/WARN-ON.cmake

@@ -0,0 +1,3 @@
+set(CMAKE_POLICY_WARNING_CMP0065 1)
+enable_language(C)
+add_executable(main subproject/main.c)

Tests/RunCMake/CMP0065/subproject/CMakeLists.txt

@@ -0,0 +1,22 @@
+cmake_minimum_required(VERSION 3.3)
+
+project(TestPolicyCMP0065 C)
+set(CMAKE_SHARED_LIBRARY_LINK_C_FLAGS BADFLAGS)
+
+#----------------------------------------------------------------------
+cmake_policy(SET CMP0065 OLD)
+add_executable(FooOLDBad1 main.c)
+
+#----------------------------------------------------------------------
+cmake_policy(SET CMP0065 OLD)
+add_executable(FooOLDBad2 main.c)
+set_target_properties(FooOLDBad2 PROPERTIES ENABLE_EXPORTS ON)
+
+#----------------------------------------------------------------------
+cmake_policy(SET CMP0065 NEW)
+add_executable(FooNEWGood main.c)
+
+#----------------------------------------------------------------------
+cmake_policy(SET CMP0065 NEW)
+add_executable(FooNEWBad main.c)
+set_target_properties(FooNEWBad PROPERTIES ENABLE_EXPORTS ON)

Tests/RunCMake/CMP0065/subproject/main.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+int main(int argc, char **argv)
+{
+  printf("Hello World\n");
+  return 0;
+}

Tests/RunCMake/CMakeLists.txt

@@ -104,6 +104,13 @@ add_RunCMake_test(CMP0057)
 add_RunCMake_test(CMP0059)
 add_RunCMake_test(CMP0060)
 add_RunCMake_test(CMP0064)
+
+# The test for Policy 65 requires the use of the
+# CMAKE_SHARED_LIBRARY_LINK_CXX_FLAGS variable, which both the VS and Xcode
+# generators ignore.  The policy will have no effect on those generators.
+if(NOT CMAKE_GENERATOR MATCHES "Visual Studio|Xcode")
+  add_RunCMake_test(CMP0065)
+endif()
 if(CMAKE_GENERATOR MATCHES "Make")
   add_RunCMake_test(Make)
 endif()

Tests/RunCMake/TargetPolicies/PolicyList-stderr.txt

@@ -19,6 +19,7 @@
    \* CMP0052
    \* CMP0060
    \* CMP0063
+   \* CMP0065
 
 Call Stack \(most recent call first\):
   CMakeLists.txt:3 \(include\)