Unity build: Add support for Ninja and Makefile generators

1 files changed, 55 insertions, 0 deletions

diff --git a/Help/prop_tgt/UNITY_BUILD.rst b/Help/prop_tgt/UNITY_BUILD.rst
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+UNITY_BUILD
+-----------
+
+Should the target source files be processed into batches for
+faster compilation. This feature is known as "Unity build",
+or "Jumbo build".
+
+The `C` and `CXX` source files are grouped separately.
+
+This property is initialized by the value of the
+:variable:`CMAKE_UNITY_BUILD` variable if it is set when
+a target is created.
+
+.. note ::
+
+   It's not recommended to directly set :prop_tgt:`UNITY_BUILD`
+   to `ON`, but to instead set :variable:`CMAKE_UNITY_BUILD` from
+   the command line. However, it IS recommended to set
+   :prop_tgt:`UNITY_BUILD` to `OFF` if you need to ensure that a
+   target doesn't get a unity build.
+
+The batch size can be specified by setting
+:prop_tgt:`UNITY_BUILD_BATCH_SIZE`.
+
+The batching of source files is done by adding new sources files
+wich will `#include` the source files, and exclude them from
+building by setting :prop_sf:`HEADER_FILE_ONLY` to `ON`.
+
+
+ODR (One definition rule) errors
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Since multiple source files are included into one source file,
+it can lead to ODR errors. This section contains properites
+which help fixing these errors.
+
+The source files marked by :prop_sf:`GENERATED` will be skipped
+from unity build. This applies also for the source files marked
+with :prop_sf:`SKIP_UNITY_BUILD_INCLUSION`.
+
+The source files that have :prop_sf:`COMPILE_OPTIONS`,
+:prop_sf:`COMPILE_DEFINITIONS`, :prop_sf:`COMPILE_FLAGS`, or
+:prop_sf:`INCLUDE_DIRECTORIES` will also be skipped.
+
+With the :prop_tgt:`UNITY_BUILD_CODE_BEFORE_INCLUDE` and
+:prop_tgt:`UNITY_BUILD_CODE_AFTER_INCLUDE` one can specify code
+to be injected in the unity source file before and after every
+`#include` statement.
+
+.. note ::
+
+   The order of source files defined in the `CMakeLists.txt` will
+   be preserved into the generated unity source files. This can
+   be used to manually enforce a specific grouping based on the
+   :prop_tgt:`UNITY_BUILD_BATCH_SIZE`.