Merge topic 'custom-command-dedup'

45fedf0e17 Makefile: Add policy CMP0113 to avoid duplication of custom commands
844779bdc1 cmMakefileTargetGenerator: Simplify custom command output collection

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !5204

3 files changed, 49 insertions, 0 deletions

diff --git a/Help/manual/cmake-policies.7.rst b/Help/manual/cmake-policies.7.rst
index cd1d4d3..3821dc3 100644
--- a/Help/manual/cmake-policies.7.rst
+++ b/Help/manual/cmake-policies.7.rst
@@ -57,6 +57,7 @@ Policies Introduced by CMake 3.19
 .. toctree::
    :maxdepth: 1
 
+   CMP0113: Makefile generators do not repeat custom commands from target dependencies. </policy/CMP0113>
    CMP0112: Target file component generator expressions do not add target dependencies. </policy/CMP0112>
    CMP0111: An imported target with a missing location fails during generation. </policy/CMP0111>
    CMP0110: add_test() supports arbitrary characters in test names. </policy/CMP0110>
diff --git a/Help/policy/CMP0113.rst b/Help/policy/CMP0113.rst
new file mode 100644
index 0000000..6f56902
--- /dev/null
+++ b/Help/policy/CMP0113.rst
@@ -0,0 +1,43 @@
+CMP0113
+-------
+
+.. versionadded:: 3.19
+
+:ref:`Makefile Generators` do not repeat custom commands from target
+dependencies.
+
+Consider a chain of custom commands split across two dependent targets:
+
+.. code-block:: cmake
+
+  add_custom_command(OUTPUT output-not-created
+    COMMAND ... DEPENDS ...)
+  set_property(SOURCE output-not-created PROPERTY SYMBOLIC 1)
+  add_custom_command(OUTPUT output-created
+    COMMAND ... DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/output-not-created)
+  add_custom_target(first DEPENDS output-not-created)
+  add_custom_target(second DEPENDS output-created)
+  add_dependencies(second first)
+
+In CMake 3.18 and lower, the Makefile generators put a copy of both custom
+commands in the Makefile for target ``second`` even though its dependency on
+target ``first`` ensures that the first custom command runs before the second.
+Running ``make second`` would cause the first custom command to run once in
+the ``first`` target and then again in the ``second`` target.
+
+CMake 3.19 and above prefer to not duplicate custom commands in a target that
+are already generated in other targets on which the target depends (directly or
+indirectly).  This policy provides compatibility for projects that have not
+been updated to expect the new behavior.  In particular, projects that relied
+on the duplicate execution or that did not properly set the :prop_sf:`SYMBOLIC`
+source file property may be affected.
+
+The ``OLD`` behavior for this policy is to duplicate custom commands in
+dependent targets.  The ``NEW`` behavior of this policy is to not duplicate
+custom commands in dependent targets.
+
+This policy was introduced in CMake version 3.19.  Unlike many policies,
+CMake version |release| does *not* warn when this policy is not set and
+simply uses ``OLD`` behavior.
+
+.. include:: DEPRECATED.txt
diff --git a/Help/release/dev/custom-command-dedup.rst b/Help/release/dev/custom-command-dedup.rst
new file mode 100644
index 0000000..65fa303
--- /dev/null
+++ b/Help/release/dev/custom-command-dedup.rst
@@ -0,0 +1,5 @@
+custom-command-dedup
+--------------------
+
+* :ref:`Makefile Generators` no longer repeat custom commands from target
+  dependencies.  See policy :policy:`CMP0113`.