Packages: Integrate FetchContent and find_package()

Allow FetchContent_MakeAvailable() to try a call to
find_package() first, or redirect a find_package() call to
FetchContent_MakeAvailable(). The user can set variables
to control which of these are allowed or tried by default.

Fixes: #21687

1 files changed, 17 insertions, 0 deletions

diff --git a/Help/release/dev/FetchContent_find_package_integration.rst b/Help/release/dev/FetchContent_find_package_integration.rst
new file mode 100644
index 0000000..4ca7afc
--- /dev/null
+++ b/Help/release/dev/FetchContent_find_package_integration.rst
@@ -0,0 +1,17 @@
+FetchContent_find_package_integration
+-------------------------------------
+
+* Integration has been added between the :module:`FetchContent` module and the
+  :command:`find_package` command, enabling the following new capabilities:
+
+  * :command:`FetchContent_MakeAvailable` can now try to satisfy a dependency
+    by calling :command:`find_package` first.  A new
+    :variable:`FETCHCONTENT_TRY_FIND_PACKAGE_MODE` variable controls whether
+    this is done by default for all dependencies, is opt-in per dependency,
+    or is disabled entirely.
+
+  * :command:`find_package` can be re-routed to call
+    :command:`FetchContent_MakeAvailable` instead.  A new read-only
+    :variable:`CMAKE_FIND_PACKAGE_REDIRECTS_DIR` variable points to a
+    directory where config package files can be located to facilitate these
+    re-routed calls.