1 files changed, 55 insertions, 23 deletions

diff --git a/Source/cmOptionCommand.cxx b/Source/cmOptionCommand.cxx
index 00a2d2b..006211d 100644
--- a/Source/cmOptionCommand.cxx
+++ b/Source/cmOptionCommand.cxx
@@ -2,11 +2,16 @@
    file Copyright.txt or https://cmake.org/licensing for details.  */
 #include "cmOptionCommand.h"
 
+#include <sstream>
+
 #include "cmAlgorithms.h"
 #include "cmMakefile.h"
+#include "cmPolicies.h"
 #include "cmState.h"
+#include "cmStateSnapshot.h"
 #include "cmStateTypes.h"
 #include "cmSystemTools.h"
+#include "cmake.h"
 
 class cmExecutionStatus;
 
@@ -14,19 +19,7 @@ class cmExecutionStatus;
 bool cmOptionCommand::InitialPass(std::vector<std::string> const& args,
                                   cmExecutionStatus&)
 {
-  bool argError = false;
-  if (args.size() < 2) {
-    argError = true;
-  }
-  // for VTK 4.0 we have to support the option command with more than 3
-  // arguments if CMAKE_MINIMUM_REQUIRED_VERSION is not defined, if
-  // CMAKE_MINIMUM_REQUIRED_VERSION is defined, then we can have stricter
-  // checking.
-  if (this->Makefile->GetDefinition("CMAKE_MINIMUM_REQUIRED_VERSION")) {
-    if (args.size() > 3) {
-      argError = true;
-    }
-  }
+  const bool argError = (args.size() < 2) || (args.size() > 3);
   if (argError) {
     std::string m = "called with incorrect number of arguments: ";
     m += cmJoin(args, " ");
@@ -34,23 +27,62 @@ bool cmOptionCommand::InitialPass(std::vector<std::string> const& args,
     return false;
   }
 
-  std::string initialValue = "Off";
-  // Now check and see if the value has been stored in the cache
-  // already, if so use that value and don't look for the program
+  // Determine the state of the option policy
+  bool checkAndWarn = false;
+  {
+    auto status = this->Makefile->GetPolicyStatus(cmPolicies::CMP0077);
+    const auto* existsBeforeSet =
+      this->Makefile->GetStateSnapshot().GetDefinition(args[0]);
+    switch (status) {
+      case cmPolicies::WARN:
+        checkAndWarn = (existsBeforeSet != nullptr);
+        break;
+      case cmPolicies::OLD:
+        // OLD behavior does not warn.
+        break;
+      case cmPolicies::REQUIRED_ALWAYS:
+      case cmPolicies::REQUIRED_IF_USED:
+      case cmPolicies::NEW: {
+        // See if a local variable with this name already exists.
+        // If so we ignore the option command.
+        if (existsBeforeSet) {
+          return true;
+        }
+      } break;
+    }
+  }
+
+  // See if a cache variable with this name already exists
+  // If so just make sure the doc state is correct
   cmState* state = this->Makefile->GetState();
   const char* existingValue = state->GetCacheEntryValue(args[0]);
-  if (existingValue) {
-    if (state->GetCacheEntryType(args[0]) != cmStateEnums::UNINITIALIZED) {
-      state->SetCacheEntryProperty(args[0], "HELPSTRING", args[1]);
-      return true;
-    }
-    initialValue = existingValue;
+  if (existingValue &&
+      (state->GetCacheEntryType(args[0]) != cmStateEnums::UNINITIALIZED)) {
+    state->SetCacheEntryProperty(args[0], "HELPSTRING", args[1]);
+    return true;
   }
+
+  // Nothing in the cache so add it
+  std::string initialValue = existingValue ? existingValue : "Off";
   if (args.size() == 3) {
     initialValue = args[2];
   }
-  bool init = cmSystemTools::IsOn(initialValue.c_str());
+  bool init = cmSystemTools::IsOn(initialValue);
   this->Makefile->AddCacheDefinition(args[0], init ? "ON" : "OFF",
                                      args[1].c_str(), cmStateEnums::BOOL);
+
+  if (checkAndWarn) {
+    const auto* existsAfterSet =
+      this->Makefile->GetStateSnapshot().GetDefinition(args[0]);
+    if (!existsAfterSet) {
+      std::ostringstream w;
+      w << cmPolicies::GetPolicyWarning(cmPolicies::CMP0077)
+        << "\n"
+           "For compatibility with older versions of CMake, option "
+           "is clearing the normal variable '"
+        << args[0] << "'.";
+      this->Makefile->IssueMessage(cmake::AUTHOR_WARNING, w.str());
+    }
+  }
   return true;
 }