3 files changed, 24 insertions, 0 deletions
diff --git a/Source/cmMakefile.cxx b/Source/cmMakefile.cxx
index 4ed76c7..b8a5293 100644
--- a/Source/cmMakefile.cxx
+++ b/Source/cmMakefile.cxx
@@ -4002,6 +4002,13 @@ bool cmMakefile::SetPolicy(cmPolicies::PolicyID id,
     return false;
   }
 
+  // Deprecate old policies, especially those that require a lot
+  // of code to maintain the old behavior.
+  if (status == cmPolicies::OLD && id <= cmPolicies::CMP0036) {
+    this->IssueMessage(cmake::DEPRECATION_WARNING,
+                       cmPolicies::GetPolicyDeprecatedWarning(id));
+  }
+
   this->StateSnapshot.SetPolicy(id, status);
   return true;
 }
diff --git a/Source/cmPolicies.cxx b/Source/cmPolicies.cxx
index 837557b..da3edd4 100644
--- a/Source/cmPolicies.cxx
+++ b/Source/cmPolicies.cxx
@@ -275,6 +275,22 @@ std::string cmPolicies::GetPolicyWarning(cmPolicies::PolicyID id)
   return msg.str();
 }
 
+std::string cmPolicies::GetPolicyDeprecatedWarning(cmPolicies::PolicyID id)
+{
+  std::ostringstream msg;
+  /* clang-format off */
+  msg <<
+    "The OLD behavior for policy " << idToString(id) << " "
+    "will be removed from a future version of CMake.\n"
+    "The cmake-policies(7) manual explains that the OLD behaviors of all "
+    "policies are deprecated and that a policy should be set to OLD only "
+    "under specific short-term circumstances.  Projects should be ported "
+    "to the NEW behavior and not rely on setting a policy to OLD."
+    ;
+  /* clang-format on */
+  return msg.str();
+}
+
 ///! return an error string for when a required policy is unspecified
 std::string cmPolicies::GetRequiredPolicyError(cmPolicies::PolicyID id)
 {
diff --git a/Source/cmPolicies.h b/Source/cmPolicies.h
index 120beb6..69cbc18 100644
--- a/Source/cmPolicies.h
+++ b/Source/cmPolicies.h
@@ -279,6 +279,7 @@ public:
 
   ///! return a warning string for a given policy
   static std::string GetPolicyWarning(cmPolicies::PolicyID id);
+  static std::string GetPolicyDeprecatedWarning(cmPolicies::PolicyID id);
 
   ///! return an error string for when a required policy is unspecified
   static std::string GetRequiredPolicyError(cmPolicies::PolicyID id);