Allow the Package Registry to be disabled (#14849)

When a project is packaged for redistribution the local package
registries should not be updated or consulted.  They are for developers.

Add variables to disable use of package registries globally:

* CMAKE_EXPORT_NO_PACKAGE_REGISTRY that disables the export(PACKAGE)
  command
* CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY that disables the User Package
  Registry in all the find_package calls.
* CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY that disables the
  System Package Registry in all the find_package calls.

Update documentation and unit tests.

1 files changed, 12 insertions, 0 deletions

diff --git a/Source/cmFindPackageCommand.cxx b/Source/cmFindPackageCommand.cxx
index a790e00407..55a61f5b1f 100644
--- a/Source/cmFindPackageCommand.cxx
+++ b/Source/cmFindPackageCommand.cxx
@@ -90,6 +90,18 @@ bool cmFindPackageCommand
     this->UseLib64Paths = true;
     }
 
+  // Check if User Package Registry should be disabled
+  if(this->Makefile->IsOn("CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY"))
+    {
+    this->NoUserRegistry = true;
+    }
+
+  // Check if System Package Registry should be disabled
+  if(this->Makefile->IsOn("CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY"))
+    {
+    this->NoSystemRegistry = true;
+    }
+
   // Find the current root path mode.
   this->SelectDefaultRootPathMode();