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.

Help/command/export.rst

@@ -51,4 +51,7 @@ projects find and use a package from the current project's build tree
 without help from the user.  Note that the entry in the package
 registry that this command creates works only in conjunction with a
 package configuration file (<name>Config.cmake) that works with the
-build tree.
+build tree. In some cases, for example for packaging and for system
+wide installations, it is not desirable to write the user package
+registry. If the :variable:`CMAKE_EXPORT_NO_PACKAGE_REGISTRY` variable
+is enabled, the ``export(PACKAGE)`` command will do nothing.

Help/command/find_package.rst

@@ -272,7 +272,9 @@ enabled.
    (This step is implemented only on Windows.)
 
 6. Search paths stored in the CMake :ref:`User Package Registry`.
-   This can be skipped if ``NO_CMAKE_PACKAGE_REGISTRY`` is passed.
+   This can be skipped if ``NO_CMAKE_PACKAGE_REGISTRY`` is passed or by
+   setting the :variable:`CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY`
+   to ``TRUE``.
    See the :manual:`cmake-packages(7)` manual for details on the user
    package registry.
 
@@ -285,7 +287,9 @@ enabled.
      CMAKE_SYSTEM_APPBUNDLE_PATH
 
 8. Search paths stored in the CMake :ref:`System Package Registry`.
-   This can be skipped if ``NO_CMAKE_SYSTEM_PACKAGE_REGISTRY`` is passed.
+   This can be skipped if ``NO_CMAKE_SYSTEM_PACKAGE_REGISTRY`` is passed
+   or by setting the
+   :variable:`CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY` to ``TRUE``.
    See the :manual:`cmake-packages(7)` manual for details on the system
    package registry.
 

Help/manual/cmake-packages.7.rst

@@ -564,6 +564,21 @@ containing the package configuration file.
 
 There is no system package registry on non-Windows platforms.
 
+.. _`Disabling the Package Registry`:
+
+Disabling the Package Registry
+------------------------------
+
+In some cases using the Package Registries is not desirable. CMake
+allows to disable them using the following variables:
+
+ * :variable:`CMAKE_EXPORT_NO_PACKAGE_REGISTRY` disables the
+   :command:`export(PACKAGE)` command.
+ * :variable:`CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY` disables the
+   User Package Registry in all the :command:`find_package` calls.
+ * :variable:`CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY` disables
+   the System Package Registry in all the :command:`find_package` calls.
+
 Package Registry Example
 ------------------------
 

Help/manual/cmake-variables.7.rst

@@ -109,10 +109,13 @@ Variables that Change Behavior
    /variable/CMAKE_DISABLE_FIND_PACKAGE_PackageName
    /variable/CMAKE_ERROR_DEPRECATED
    /variable/CMAKE_ERROR_ON_ABSOLUTE_INSTALL_DESTINATION
+   /variable/CMAKE_EXPORT_NO_PACKAGE_REGISTRY
    /variable/CMAKE_SYSROOT
    /variable/CMAKE_FIND_LIBRARY_PREFIXES
    /variable/CMAKE_FIND_LIBRARY_SUFFIXES
    /variable/CMAKE_FIND_NO_INSTALL_PREFIX
+   /variable/CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY
+   /variable/CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY
    /variable/CMAKE_FIND_PACKAGE_WARN_NO_MODULE
    /variable/CMAKE_FIND_ROOT_PATH
    /variable/CMAKE_FIND_ROOT_PATH_MODE_INCLUDE

Help/variable/CMAKE_EXPORT_NO_PACKAGE_REGISTRY.rst

@@ -0,0 +1,11 @@
+CMAKE_EXPORT_NO_PACKAGE_REGISTRY
+--------------------------------
+
+Disable the :command:`export(PACKAGE)` command.
+
+In some cases, for example for packaging and for system wide
+installations, it is not desirable to write the user package registry.
+If the :variable:`CMAKE_EXPORT_NO_PACKAGE_REGISTRY` variable is enabled,
+the :command:`export(PACKAGE)` command will do nothing.
+
+See also :ref:`Disabling the Package Registry`.

Help/variable/CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY.rst

@@ -0,0 +1,13 @@
+CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY
+--------------------------------------
+
+Skip :ref:`User Package Registry` in :command:`find_package` calls.
+
+In some cases, for example to locate only system wide installations, it
+is not desirable to use the :ref:`User Package Registry` when searching
+for packages. If the :variable:`CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY`
+variable is enabled, all the :command:`find_package` commands will skip
+the :ref:`User Package Registry` as if they were called with the
+``NO_CMAKE_PACKAGE_REGISTRY`` argument.
+
+See also :ref:`Disabling the Package Registry`.

Help/variable/CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY.rst

@@ -0,0 +1,13 @@
+CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY
+---------------------------------------------
+
+Skip :ref:`System Package Registry` in :command:`find_package` calls.
+
+In some cases, it is not desirable to use the
+:ref:`System Package Registry` when searching for packages. If the
+:variable:`CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY` variable is
+enabled, all the :command:`find_package` commands will skip
+the :ref:`System Package Registry` as if they were called with the
+``NO_CMAKE_SYSTEM_PACKAGE_REGISTRY`` argument.
+
+See also :ref:`Disabling the Package Registry`.

Source/cmExportCommand.cxx

@@ -285,6 +285,13 @@ bool cmExportCommand::HandlePackage(std::vector<std::string> const& args)
     return false;
     }
 
+  // If the CMAKE_EXPORT_NO_PACKAGE_REGISTRY variable is set the command
+  // export(PACKAGE) does nothing.
+  if(this->Makefile->IsOn("CMAKE_EXPORT_NO_PACKAGE_REGISTRY"))
+    {
+    return true;
+    }
+
   // We store the current build directory in the registry as a value
   // named by a hash of its own content.  This is deterministic and is
   // unique with high probability.

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();
 

Tests/FindPackageTest/CMakeLists.txt

@@ -331,7 +331,7 @@ try_compile(EXPORTER_COMPILED
   ${FindPackageTest_BINARY_DIR}/Exporter-build
   ${FindPackageTest_SOURCE_DIR}/Exporter
   CMakeTestExportPackage dummy
-  CMAKE_FLAGS
+  CMAKE_FLAGS "-UCMAKE_EXPORT_NO_PACKAGE_REGISTRY"
     -Dversion=${version}
   OUTPUT_VARIABLE output)
 message(STATUS "Searching for export(PACKAGE) test project")
@@ -339,6 +339,36 @@ set(CMakeTestExportPackage_DIR "" CACHE FILEPATH
   "Wipe out find results for testing." FORCE)
 find_package(CMakeTestExportPackage 1.${version} EXACT REQUIRED)
 
+message(STATUS "Searching for export(PACKAGE) test project with CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY=TRUE")
+set(CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY TRUE)
+set(CMakeTestExportPackage_DIR "" CACHE FILEPATH
+  "Wipe out find results for testing." FORCE)
+find_package(CMakeTestExportPackage  1.${version} EXACT QUIET)
+if(CMakeTestExportPackage_FOUND)
+  message(SEND_ERROR "CMakeTestExportPackage should not be FOUND!")
+endif()
+unset(CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY)
+
+message(STATUS "Remove export(PACKAGE) test project")
+file(REMOVE_RECURSE ${FindPackageTest_BINARY_DIR}/Exporter-build)
+set(CMakeTestExportPackage_DIR "" CACHE FILEPATH
+  "Wipe out find results for testing." FORCE)
+find_package(CMakeTestExportPackage QUIET) # Should clean the user package cache
+#
+message(STATUS "Preparing export(PACKAGE) test project with CMAKE_EXPORT_NO_PACKAGE_REGISTRY=TRUE")
+try_compile(EXPORTER_COMPILED
+  ${FindPackageTest_BINARY_DIR}/Exporter-build
+  ${FindPackageTest_SOURCE_DIR}/Exporter
+  CMakeTestExportPackage dummy
+  CMAKE_FLAGS "-DCMAKE_EXPORT_NO_PACKAGE_REGISTRY:BOOL=TRUE"
+    -Dversion=${version}
+  OUTPUT_VARIABLE output)
+message(STATUS "Searching for export(PACKAGE) test project")
+find_package(CMakeTestExportPackage 1.${version} EXACT QUIET)
+if(CMakeTestExportPackage_FOUND)
+  message(SEND_ERROR "CMakeTestExportPackage should not be FOUND!")
+endif()
+
 #-----------------------------------------------------------------------------
 # Test configure_package_config_file().