5 files changed, 57 insertions, 2 deletions
diff --git a/Help/manual/cmake-properties.7.rst b/Help/manual/cmake-properties.7.rst
index 9031e9c..4103806 100644
--- a/Help/manual/cmake-properties.7.rst
+++ b/Help/manual/cmake-properties.7.rst
@@ -346,6 +346,7 @@ Properties on Targets
    /prop_tgt/UNITY_BUILD_BATCH_SIZE
    /prop_tgt/UNITY_BUILD_CODE_AFTER_INCLUDE
    /prop_tgt/UNITY_BUILD_CODE_BEFORE_INCLUDE
+   /prop_tgt/UNITY_BUILD_MODE
    /prop_tgt/VERSION
    /prop_tgt/VISIBILITY_INLINES_HIDDEN
    /prop_tgt/VS_CONFIGURATION_TYPE
@@ -484,6 +485,7 @@ Properties on Source Files
    /prop_sf/Swift_DEPENDENCIES_FILE
    /prop_sf/Swift_DIAGNOSTICS_FILE
    /prop_sf/SYMBOLIC
+   /prop_sf/UNITY_GROUP
    /prop_sf/VS_COPY_TO_OUT_DIR
    /prop_sf/VS_CSHARP_tagname
    /prop_sf/VS_DEPLOYMENT_CONTENT
diff --git a/Help/prop_sf/UNITY_GROUP.rst b/Help/prop_sf/UNITY_GROUP.rst
new file mode 100644
index 0000000..ec6b0f6
--- /dev/null
+++ b/Help/prop_sf/UNITY_GROUP.rst
@@ -0,0 +1,5 @@
+UNITY_GROUP
+-----------
+
+This property controls which *bucket* the source will be part of when
+the :prop_tgt:`UNITY_BUILD_MODE` is set to ``GROUP``.
diff --git a/Help/prop_tgt/UNITY_BUILD.rst b/Help/prop_tgt/UNITY_BUILD.rst
index 479802e..e140952 100644
--- a/Help/prop_tgt/UNITY_BUILD.rst
+++ b/Help/prop_tgt/UNITY_BUILD.rst
@@ -5,8 +5,28 @@ When this property is set to true, the target source files will be combined
 into batches for faster compilation.  This is done by creating a (set of)
 unity sources which ``#include`` the original sources, then compiling these
 unity sources instead of the originals.  This is known as a *Unity* or *Jumbo*
-build.  The :prop_tgt:`UNITY_BUILD_BATCH_SIZE` property controls the upper
-limit on how many sources can be combined per unity source file.
+build.
+
+CMake provides different algorithms for selecting which sources are grouped
+together into a *bucket*. Algorithm selection is decided by the
+:prop_tgt:`UNITY_BUILD_MODE` target property, which has the following acceptable
+values:
+
+* ``BATCH``
+  When in this mode CMake determines which files are grouped together.
+  The :prop_tgt:`UNITY_BUILD_BATCH_SIZE` property controls the upper limit on
+  how many sources can be combined per unity source file.
+
+* ``GROUP``
+  When in this mode each target explicitly specifies how to group
+  source files. Each source file that has the same
+  :prop_sf:`UNITY_GROUP` value will be grouped together. Any sources
+  that don't have this property will be compiled individually. The
+  :prop_tgt:`UNITY_BUILD_BATCH_SIZE` property is ignored when using
+  this mode.
+
+If no explicit :prop_tgt:`UNITY_BUILD_MODE` has been specified, CMake will
+default to ``BATCH``.
 
 Unity builds are not currently supported for all languages.  CMake version
 |release| supports combining ``C`` and ``CXX`` source files.  For targets that
diff --git a/Help/prop_tgt/UNITY_BUILD_MODE.rst b/Help/prop_tgt/UNITY_BUILD_MODE.rst
new file mode 100644
index 0000000..cbc4989
--- /dev/null
+++ b/Help/prop_tgt/UNITY_BUILD_MODE.rst
@@ -0,0 +1,22 @@
+UNITY_BUILD_MODE
+----------------
+
+CMake provides different algorithms for selecting which sources are grouped
+together into a *bucket*. Selection is decided by this property,
+which has the following acceptable values:
+
+* ``BATCH``
+  When in this mode CMake determines which files are grouped together.
+  The :prop_tgt:`UNITY_BUILD_BATCH_SIZE` property controls the upper limit on
+  how many sources can be combined per unity source file.
+
+* ``GROUP``
+  When in this mode each target explicitly specifies how to group
+  source files. Each source file that has the same
+  :prop_sf:`UNITY_GROUP` value will be grouped together. Any sources
+  that don't have this property will be compiled individually. The
+  :prop_tgt:`UNITY_BUILD_BATCH_SIZE` property is ignored when using
+  this mode.
+
+If no explicit :prop_tgt:`UNITY_BUILD_MODE` has been specified, CMake will
+default to ``BATCH``.
diff --git a/Help/release/dev/grouped-unity-build-mode.rst b/Help/release/dev/grouped-unity-build-mode.rst
new file mode 100644
index 0000000..802de4a
--- /dev/null
+++ b/Help/release/dev/grouped-unity-build-mode.rst
@@ -0,0 +1,6 @@
+grouped-unity-build-mode
+------------------------
+
+* The :prop_tgt:`UNITY_BUILD_MODE` target property was added to tell
+  generators which algorithm to use for grouping included source
+  files.