From 30268b46f8237f25c82858693c000f5da8ede6ad Mon Sep 17 00:00:00 2001
From: Stephen Kelly <steveire@gmail.com>
Date: Thu, 31 Jan 2013 11:18:49 +0100
Subject: [PATCH] Handle reading empty properties defined by the link
 interface.

This was segfaulting before.
---
 Source/cmGeneratorExpressionEvaluator.cxx |  4 +++-
 Tests/CompatibleInterface/CMakeLists.txt  | 14 +++++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/Source/cmGeneratorExpressionEvaluator.cxx b/Source/cmGeneratorExpressionEvaluator.cxx
index f74b69e5f..55f54e464 100644
--- a/Source/cmGeneratorExpressionEvaluator.cxx
+++ b/Source/cmGeneratorExpressionEvaluator.cxx
@@ -465,9 +465,11 @@ static const struct TargetPropertyNode : public cmGeneratorExpressionNode
       if (target->IsLinkInterfaceDependentStringProperty(propertyName,
                                                          context->Config))
         {
-        return target->GetLinkInterfaceDependentStringProperty(
+        const char *propContent =
+                              target->GetLinkInterfaceDependentStringProperty(
                                                 propertyName,
                                                 context->Config);
+        return propContent ? propContent : "";
         }
 
       return std::string();
diff --git a/Tests/CompatibleInterface/CMakeLists.txt b/Tests/CompatibleInterface/CMakeLists.txt
index 259b5a186..329510b05 100644
--- a/Tests/CompatibleInterface/CMakeLists.txt
+++ b/Tests/CompatibleInterface/CMakeLists.txt
@@ -48,10 +48,22 @@ target_compile_definitions(CompatibleInterface
 add_library(iface2 SHARED iface2.cpp)
 generate_export_header(iface2)
 
+set_property(TARGET iface2 APPEND PROPERTY
+  COMPATIBLE_INTERFACE_STRING
+    Iface2_PROP
+)
+
 # For the LINK_LIBRARIES and related properties, we should not evaluate
 # properties defined only in the interface - they should be implicitly zero
 set_property(TARGET iface2
   APPEND PROPERTY
     LINK_INTERFACE_LIBRARIES $<$<BOOL:$<TARGET_PROPERTY:BOOL_PROP4>>:nonexistant>
 )
-target_link_libraries(CompatibleInterface iface2)
+target_link_libraries(CompatibleInterface iface2
+      $<$<BOOL:$<TARGET_PROPERTY:Iface2_PROP>>:nonexistant>
+)
+# Test that this does not segfault:
+target_compile_definitions(CompatibleInterface
+  PRIVATE
+    $<$<BOOL:$<TARGET_PROPERTY:Iface2_PROP>>:SOME_DEFINE>
+)