find_package(): Add policy to remove the FindQt module

Removing FindQt.cmake gives Qt upstream a path forward to export its
own QtConfig.cmake files which can be found by find_package()
without having to explicitly specify CONFIG. Projects that still
want to use Qt3/4 can call find_package(Qt[34]), include(FindQt),
or add FindQt.cmake to their CMAKE_MODULE_PATH.

5 files changed, 46 insertions, 4 deletions

diff --git a/Source/cmFindPackageCommand.cxx b/Source/cmFindPackageCommand.cxx
index 97c1d7d..bf928fc 100644
--- a/Source/cmFindPackageCommand.cxx
+++ b/Source/cmFindPackageCommand.cxx
@@ -111,6 +111,8 @@ cmFindPackageCommand::cmFindPackageCommand()
   this->SortOrder = None;
   this->SortDirection = Asc;
   this->AppendSearchPathGroups();
+
+  this->DeprecatedFindModules["Qt"] = cmPolicies::CMP0084;
 }
 
 void cmFindPackageCommand::AppendSearchPathGroups()
@@ -653,8 +655,31 @@ bool cmFindPackageCommand::FindModule(bool& found)
   std::string module = "Find";
   module += this->Name;
   module += ".cmake";
-  std::string mfile = this->Makefile->GetModulesFile(module.c_str());
+  bool system = false;
+  std::string mfile = this->Makefile->GetModulesFile(module.c_str(), system);
   if (!mfile.empty()) {
+    if (system) {
+      auto it = this->DeprecatedFindModules.find(this->Name);
+      if (it != this->DeprecatedFindModules.end()) {
+        cmPolicies::PolicyStatus status =
+          this->Makefile->GetPolicyStatus(it->second);
+        switch (status) {
+          case cmPolicies::WARN: {
+            std::ostringstream e;
+            e << cmPolicies::GetPolicyWarning(it->second) << "\n";
+            this->Makefile->IssueMessage(cmake::AUTHOR_WARNING, e.str());
+            CM_FALLTHROUGH;
+          }
+          case cmPolicies::OLD:
+            break;
+          case cmPolicies::REQUIRED_IF_USED:
+          case cmPolicies::REQUIRED_ALWAYS:
+          case cmPolicies::NEW:
+            return true;
+        }
+      }
+    }
+
     // Load the module we found, and set "<name>_FIND_MODULE" to true
     // while inside it.
     found = true;
diff --git a/Source/cmFindPackageCommand.h b/Source/cmFindPackageCommand.h
index 48f17ef..05bad49 100644
--- a/Source/cmFindPackageCommand.h
+++ b/Source/cmFindPackageCommand.h
@@ -4,6 +4,7 @@
 #define cmFindPackageCommand_h
 
 #include "cmConfigure.h" // IWYU pragma: keep
+#include "cmPolicies.h"
 
 #include "cm_kwiml.h"
 #include <cstddef>
@@ -148,6 +149,8 @@ private:
   };
   std::map<std::string, OriginalDef> OriginalDefs;
 
+  std::map<std::string, cmPolicies::PolicyID> DeprecatedFindModules;
+
   std::string Name;
   std::string Variable;
   std::string Version;
diff --git a/Source/cmMakefile.cxx b/Source/cmMakefile.cxx
index 0d42fb0..790f6e0 100644
--- a/Source/cmMakefile.cxx
+++ b/Source/cmMakefile.cxx
@@ -3500,7 +3500,8 @@ void cmMakefile::DisplayStatus(const char* message, float s) const
   cm->UpdateProgress(message, s);
 }
 
-std::string cmMakefile::GetModulesFile(const char* filename) const
+std::string cmMakefile::GetModulesFile(const char* filename,
+                                       bool& system) const
 {
   std::string result;
 
@@ -3547,8 +3548,10 @@ std::string cmMakefile::GetModulesFile(const char* filename) const
   // Normally, prefer the files found in CMAKE_MODULE_PATH. Only when the file
   // from which we are being called is located itself in CMAKE_ROOT, then
   // prefer results from CMAKE_ROOT depending on the policy setting.
+  system = false;
   result = moduleInCMakeModulePath;
   if (result.empty()) {
+    system = true;
     result = moduleInCMakeRoot;
   }
 
@@ -3571,11 +3574,13 @@ std::string cmMakefile::GetModulesFile(const char* filename) const
           CM_FALLTHROUGH;
         }
         case cmPolicies::OLD:
+          system = false;
           result = moduleInCMakeModulePath;
           break;
         case cmPolicies::REQUIRED_IF_USED:
         case cmPolicies::REQUIRED_ALWAYS:
         case cmPolicies::NEW:
+          system = true;
           result = moduleInCMakeRoot;
           break;
       }
diff --git a/Source/cmMakefile.h b/Source/cmMakefile.h
index d8176d9..aa94054 100644
--- a/Source/cmMakefile.h
+++ b/Source/cmMakefile.h
@@ -689,7 +689,13 @@ public:
   /**
    * Return a location of a file in cmake or custom modules directory
    */
-  std::string GetModulesFile(const char* name) const;
+  std::string GetModulesFile(const char* name) const
+  {
+    bool system;
+    return this->GetModulesFile(name, system);
+  }
+
+  std::string GetModulesFile(const char* name, bool& system) const;
 
   ///! Set/Get a property of this directory
   void SetProperty(const std::string& prop, const char* value);
diff --git a/Source/cmPolicies.h b/Source/cmPolicies.h
index 52ef470..6b1314f 100644
--- a/Source/cmPolicies.h
+++ b/Source/cmPolicies.h
@@ -246,7 +246,10 @@ class cmMakefile;
          "in caller.",                                                        \
          3, 14, 0, cmPolicies::WARN)                                          \
   SELECT(POLICY, CMP0083, "Add PIE options when linking executable.", 3, 14,  \
-         0, cmPolicies::WARN)
+         0, cmPolicies::WARN)                                                 \
+  SELECT(POLICY, CMP0084,                                                     \
+         "The FindQt module does not exist for find_package().", 3, 14, 0,    \
+         cmPolicies::WARN)
 
 #define CM_SELECT_ID(F, A1, A2, A3, A4, A5, A6) F(A1)
 #define CM_FOR_EACH_POLICY_ID(POLICY)                                         \