From f6fd0abc5bbfa7d677cd090ba8e2894d96afdde8 Mon Sep 17 00:00:00 2001
From: Brad King <brad.king@kitware.com>
Date: Mon, 5 Sep 2016 09:04:30 -0400
Subject: Genex: Diagnose invalid LINK_ONLY usage instead of crashing

When `$<LINK_ONLY:...>` is used outside of linking we may evaluate it
without a `dagChecker`.  Do not dereference the NULL pointer and issue a
diagnostic instead.

Closes: #16287
---
 Source/cmGeneratorExpressionNode.cxx                          | 11 ++++++++---
 .../GeneratorExpression/LINK_ONLY-not-linking-result.txt      |  1 +
 .../GeneratorExpression/LINK_ONLY-not-linking-stderr.txt      |  8 ++++++++
 .../RunCMake/GeneratorExpression/LINK_ONLY-not-linking.cmake  |  1 +
 Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake         |  1 +
 5 files changed, 19 insertions(+), 3 deletions(-)
 create mode 100644 Tests/RunCMake/GeneratorExpression/LINK_ONLY-not-linking-result.txt
 create mode 100644 Tests/RunCMake/GeneratorExpression/LINK_ONLY-not-linking-stderr.txt
 create mode 100644 Tests/RunCMake/GeneratorExpression/LINK_ONLY-not-linking.cmake

diff --git a/Source/cmGeneratorExpressionNode.cxx b/Source/cmGeneratorExpressionNode.cxx
index 44e9ce1..c19a741 100644
--- a/Source/cmGeneratorExpressionNode.cxx
+++ b/Source/cmGeneratorExpressionNode.cxx
@@ -672,15 +672,20 @@ static const struct LinkOnlyNode : public cmGeneratorExpressionNode
   LinkOnlyNode() {}
 
   std::string Evaluate(const std::vector<std::string>& parameters,
-                       cmGeneratorExpressionContext* /*context*/,
-                       const GeneratorExpressionContent* /*content*/,
+                       cmGeneratorExpressionContext* context,
+                       const GeneratorExpressionContent* content,
                        cmGeneratorExpressionDAGChecker* dagChecker) const
     CM_OVERRIDE
   {
+    if (!dagChecker) {
+      reportError(context, content->GetOriginalExpression(),
+                  "$<LINK_ONLY:...> may only be used for linking");
+      return std::string();
+    }
     if (!dagChecker->GetTransitivePropertiesOnly()) {
       return parameters.front();
     }
-    return "";
+    return std::string();
   }
 } linkOnlyNode;
 
diff --git a/Tests/RunCMake/GeneratorExpression/LINK_ONLY-not-linking-result.txt b/Tests/RunCMake/GeneratorExpression/LINK_ONLY-not-linking-result.txt
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/Tests/RunCMake/GeneratorExpression/LINK_ONLY-not-linking-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/GeneratorExpression/LINK_ONLY-not-linking-stderr.txt b/Tests/RunCMake/GeneratorExpression/LINK_ONLY-not-linking-stderr.txt
new file mode 100644
index 0000000..cded130
--- /dev/null
+++ b/Tests/RunCMake/GeneratorExpression/LINK_ONLY-not-linking-stderr.txt
@@ -0,0 +1,8 @@
+CMake Error at LINK_ONLY-not-linking.cmake:1 \(add_custom_target\):
+  Error evaluating generator expression:
+
+    \$<LINK_ONLY:something>
+
+  \$<LINK_ONLY:...> may only be used for linking
+Call Stack \(most recent call first\):
+  CMakeLists.txt:3 \(include\)
diff --git a/Tests/RunCMake/GeneratorExpression/LINK_ONLY-not-linking.cmake b/Tests/RunCMake/GeneratorExpression/LINK_ONLY-not-linking.cmake
new file mode 100644
index 0000000..16db0a2
--- /dev/null
+++ b/Tests/RunCMake/GeneratorExpression/LINK_ONLY-not-linking.cmake
@@ -0,0 +1 @@
+add_custom_target(Custom ALL COMMAND ${CMAKE_COMMAND} -E echo $<LINK_ONLY:something>)
diff --git a/Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake b/Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake
index 625bab2..f5584d5 100644
--- a/Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake
+++ b/Tests/RunCMake/GeneratorExpression/RunCMakeTest.cmake
@@ -29,6 +29,7 @@ run_cmake(COMPILE_LANGUAGE-unknown-lang)
 run_cmake(TARGET_FILE-recursion)
 run_cmake(OUTPUT_NAME-recursion)
 run_cmake(TARGET_PROPERTY-LOCATION)
+run_cmake(LINK_ONLY-not-linking)
 
 run_cmake(ImportedTarget-TARGET_PDB_FILE)
 if(LINKER_SUPPORTS_PDB)
-- 
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