1 files changed, 57 insertions, 5 deletions

diff --git a/Source/cmMarkAsAdvancedCommand.cxx b/Source/cmMarkAsAdvancedCommand.cxx
index ca46e14..45043fa 100644
--- a/Source/cmMarkAsAdvancedCommand.cxx
+++ b/Source/cmMarkAsAdvancedCommand.cxx
@@ -4,8 +4,11 @@
 
 #include "cmExecutionStatus.h"
 #include "cmMakefile.h"
+#include "cmMessageType.h"
+#include "cmPolicies.h"
 #include "cmState.h"
 #include "cmStateTypes.h"
+#include "cmStringAlgorithms.h"
 #include "cmSystemTools.h"
 #include "cmake.h"
 
@@ -28,14 +31,63 @@ bool cmMarkAsAdvancedCommand(std::vector<std::string> const& args,
     }
     i = 1;
   }
+
+  cmMakefile& mf = status.GetMakefile();
+  cmState* state = mf.GetState();
+
   for (; i < args.size(); ++i) {
     std::string const& variable = args[i];
-    cmState* state = status.GetMakefile().GetState();
-    if (!state->GetCacheEntryValue(variable)) {
-      status.GetMakefile().GetCMakeInstance()->AddCacheEntry(
-        variable, nullptr, nullptr, cmStateEnums::UNINITIALIZED);
-      overwrite = true;
+
+    bool issueMessage = false;
+    bool oldBehavior = false;
+    bool ignoreVariable = false;
+    switch (mf.GetPolicyStatus(cmPolicies::CMP0102)) {
+      case cmPolicies::WARN:
+        if (mf.PolicyOptionalWarningEnabled("CMAKE_POLICY_WARNING_CMP0102")) {
+          if (!state->GetCacheEntryValue(variable)) {
+            issueMessage = true;
+          }
+        }
+        CM_FALLTHROUGH;
+      case cmPolicies::OLD:
+        oldBehavior = true;
+        break;
+      case cmPolicies::NEW:
+      case cmPolicies::REQUIRED_IF_USED:
+      case cmPolicies::REQUIRED_ALWAYS:
+        if (!state->GetCacheEntryValue(variable)) {
+          ignoreVariable = true;
+        }
+        break;
+    }
+
+    // First see if we should issue a message about CMP0102
+    if (issueMessage) {
+      std::string err = cmStrCat(
+        "Policy CMP0102 is not set: The variable named \"", variable,
+        "\" is not in the cache. This results in an empty cache entry which "
+        "is no longer created when policy CMP0102 is set to NEW. Run \"cmake "
+        "--help-policy CMP0102\" for policy details. Use the cmake_policy "
+        "command to set the policy and suppress this warning.");
+      mf.IssueMessage(MessageType::AUTHOR_WARNING, err);
     }
+
+    // If it's not in the cache and we're using the new behavior, nothing to
+    // see here.
+    if (ignoreVariable) {
+      continue;
+    }
+
+    // Check if we want the old behavior of making a dummy cache entry.
+    if (oldBehavior) {
+      if (!state->GetCacheEntryValue(variable)) {
+        status.GetMakefile().GetCMakeInstance()->AddCacheEntry(
+          variable, nullptr, nullptr, cmStateEnums::UNINITIALIZED);
+        overwrite = true;
+      }
+    }
+
+    // We need a cache entry to do this.
     if (!state->GetCacheEntryValue(variable)) {
       cmSystemTools::Error("This should never happen...");
       return false;