ExternalProject: Support not initializing any submodules

Fixes #15592

1 files changed, 23 insertions, 0 deletions

diff --git a/Help/policy/CMP0097.rst b/Help/policy/CMP0097.rst
new file mode 100644
index 0000000..8a5ff88
--- /dev/null
+++ b/Help/policy/CMP0097.rst
@@ -0,0 +1,23 @@
+CMP0097
+-------
+
+:command:`ExternalProject_Add` with ``GIT_SUBMODULES ""`` initializes no
+submodules.
+
+The module provides a ``GIT_SUBMODULES`` option which controls what submodules
+to initialize and update. Starting with CMake 3.16, explicitly setting
+``GIT_SUBMODULES`` to an empty string means no submodules will be initialized
+or updated.
+
+This policy provides compatibility for projects that have not been updated
+to expect the new behavior.
+
+The ``OLD`` behavior for this policy is for ``GIT_SUBMODULES`` when set to
+an empty string to initialize and update all git submodules.
+The ``New`` behavior for this policy is for ``GIT_SUBMODULES`` when set to
+an empty string to initialize and update no git submodules.
+
+This policy was introduced in CMake version 3.16.  Use the
+:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly.
+Unlike most policies, CMake version |release| does *not* warn
+when this policy is not set and simply uses ``OLD`` behavior.