CMP0126: Add control for warnings

Fixes: #22353

2 files changed, 22 insertions, 5 deletions

diff --git a/Source/cmMakefile.cxx b/Source/cmMakefile.cxx
index d2d34f9..c970abe 100644
--- a/Source/cmMakefile.cxx
+++ b/Source/cmMakefile.cxx
@@ -1962,9 +1962,26 @@ void cmMakefile::AddCacheDefinition(const std::string& name, const char* value,
     }
   }
   this->GetCMakeInstance()->AddCacheEntry(name, value, doc, type);
-  if (this->GetPolicyStatus(cmPolicies::CMP0126) != cmPolicies::NEW) {
-    // if there was a definition then remove it
-    this->StateSnapshot.RemoveDefinition(name);
+  switch (this->GetPolicyStatus(cmPolicies::CMP0126)) {
+    case cmPolicies::WARN:
+      if (this->PolicyOptionalWarningEnabled("CMAKE_POLICY_WARNING_CMP0126") &&
+          this->IsNormalDefinitionSet(name)) {
+        this->IssueMessage(
+          MessageType::AUTHOR_WARNING,
+          cmStrCat(cmPolicies::GetPolicyWarning(cmPolicies::CMP0126),
+                   "\nFor compatibility with older versions of CMake, normal "
+                   "variable \"",
+                   name, "\" will be removed from the current scope."));
+      }
+      CM_FALLTHROUGH;
+    case cmPolicies::OLD:
+      // if there was a definition then remove it
+      this->StateSnapshot.RemoveDefinition(name);
+      break;
+    case cmPolicies::NEW:
+    case cmPolicies::REQUIRED_IF_USED:
+    case cmPolicies::REQUIRED_ALWAYS:
+      break;
   }
 }
 
diff --git a/Source/cmProjectCommand.cxx b/Source/cmProjectCommand.cxx
index acdb09f..6950c19 100644
--- a/Source/cmProjectCommand.cxx
+++ b/Source/cmProjectCommand.cxx
@@ -71,7 +71,7 @@ bool cmProjectCommand(std::vector<std::string> const& args,
   // CMAKE_PROJECT_NAME will match PROJECT_NAME, and cmake --build
   // will work.
   if (!mf.GetDefinition("CMAKE_PROJECT_NAME") || mf.IsRootMakefile()) {
-    mf.AddDefinition("CMAKE_PROJECT_NAME", projectName);
+    mf.RemoveDefinition("CMAKE_PROJECT_NAME");
     mf.AddCacheDefinition("CMAKE_PROJECT_NAME", projectName,
                           "Value Computed by CMake", cmStateEnums::STATIC);
   }
@@ -395,7 +395,7 @@ static void TopLevelCMakeVarCondSet(cmMakefile& mf, std::string const& name,
   // in the same CMakeLists.txt file, and it is the top level
   // CMakeLists.txt file, then go with the last one.
   if (!mf.GetDefinition(name) || mf.IsRootMakefile()) {
-    mf.AddDefinition(name, value);
+    mf.RemoveDefinition(name);
     mf.AddCacheDefinition(name, value, "Value Computed by CMake",
                           cmStateEnums::STATIC);
   }