Document the double-colon behavior of DIR ccaches

(cherry picked from commit 5ba6e02a7b96ddd15dde01db0f9aff3d65773a8e)

ticket: 8789
version_fixed: 1.17.1

diff --git a/doc/basic/ccache_def.rst b/doc/basic/ccache_def.rst
index d147f0d7aa99254a277ef8a40823a1dda5510099..53542adde9346e0aa9c7115c0705350539f34c80 100644 (file)
--- a/doc/basic/ccache_def.rst
+++ b/doc/basic/ccache_def.rst
@@ -51,6 +51,13 @@ library.
    requirement is for parent directory to exist and the current
    process must have permissions to create the directory if it does
    not exist. See :ref:`col_ccache` for details.  New in release 1.10.
+   The following residual forms are supported:
+
+   * DIR:dirname
+   * DIR::dirpath/filename - a single cache within the directory
+
+   Switching to a ccache of the latter type causes it to become the
+   primary for the directory.
 
 #. **FILE** caches are the simplest and most portable. A simple flat
    file format is used to store one credential after another.  This is