Allow users to specify defaults for unset policies

Check CMAKE_POLICY_DEFAULT_CMP<NNNN> for a default when policy CMP<NNNN>
would otherwise be left unset.  This allows users to set policies on the
command line when the project does not set them.  One may do this to
quiet warnings or test whether a project will build with new behavior
without modifying code.  There may also be cases when users want to
build an existing project release using new behavior for policies
unknown to the project at the time of the release.

1 files changed, 37 insertions, 2 deletions

diff --git a/Source/cmPolicies.cxx b/Source/cmPolicies.cxx
index d147a3b..fccf0cc 100644
--- a/Source/cmPolicies.cxx
+++ b/Source/cmPolicies.cxx
@@ -565,9 +565,14 @@ bool cmPolicies::ApplyPolicyVersion(cmMakefile *mf,
         {
         ancientPolicies.push_back(i->first);
         }
-      else if (!mf->SetPolicy(i->second->ID, cmPolicies::WARN))
+      else
         {
-        return false;
+        cmPolicies::PolicyStatus status = cmPolicies::WARN;
+        if(!this->GetPolicyDefault(mf, i->second->IDString, &status) ||
+           !mf->SetPolicy(i->second->ID, status))
+          {
+          return false;
+          }
         }
       }
     else
@@ -591,6 +596,36 @@ bool cmPolicies::ApplyPolicyVersion(cmMakefile *mf,
   return true;
 }
 
+//----------------------------------------------------------------------------
+bool cmPolicies::GetPolicyDefault(cmMakefile* mf, std::string const& policy,
+                                  cmPolicies::PolicyStatus* defaultSetting)
+{
+  std::string defaultVar = "CMAKE_POLICY_DEFAULT_" + policy;
+  std::string defaultValue = mf->GetSafeDefinition(defaultVar.c_str());
+  if(defaultValue == "NEW")
+    {
+    *defaultSetting = cmPolicies::NEW;
+    }
+  else if(defaultValue == "OLD")
+    {
+    *defaultSetting = cmPolicies::OLD;
+    }
+  else if(defaultValue == "")
+    {
+    *defaultSetting = cmPolicies::WARN;
+    }
+  else
+    {
+    cmOStringStream e;
+    e << defaultVar << " has value \"" << defaultValue
+      << "\" but must be \"OLD\", \"NEW\", or \"\" (empty).";
+    mf->IssueMessage(cmake::FATAL_ERROR, e.str().c_str());
+    return false;
+    }
+
+  return true;
+}
+
 bool cmPolicies::GetPolicyID(const char *id, cmPolicies::PolicyID &pid)
 {
   if (!id || strlen(id) < 1)