Deprecate compatibility with CMake versions older than 2.8.12

Issue a deprecation warning on calls to `cmake_minimum_required` or
`cmake_policy` that set policies based on versions older than 2.8.12.
Note that the effective policy version includes `...<max>` treatment.
This is important in combination with commit ca24b70d31 (Export: Specify
a policy range in exported files, 2020-05-16, v3.18.0-rc1~133^2).

1 files changed, 10 insertions, 2 deletions

diff --git a/Source/cmPolicies.h b/Source/cmPolicies.h
index 49dadc7..bba8b03 100644
--- a/Source/cmPolicies.h
+++ b/Source/cmPolicies.h
@@ -399,12 +399,20 @@ public:
   //! Get the default status for a policy
   static cmPolicies::PolicyStatus GetPolicyStatus(cmPolicies::PolicyID id);
 
+  enum class WarnCompat
+  {
+    Off,
+    On
+  };
+
   //! Set a policy level for this listfile
   static bool ApplyPolicyVersion(cmMakefile* mf,
                                  std::string const& version_min,
-                                 std::string const& version_max);
+                                 std::string const& version_max,
+                                 WarnCompat warnCompat);
   static bool ApplyPolicyVersion(cmMakefile* mf, unsigned int majorVer,
-                                 unsigned int minorVer, unsigned int patchVer);
+                                 unsigned int minorVer, unsigned int patchVer,
+                                 WarnCompat warnCompat);
 
   //! return a warning string for a given policy
   static std::string GetPolicyWarning(cmPolicies::PolicyID id);