ExternalProject: add LOG_PATCH option to log the patch command

Most steps support the logging into a file but the patch command is a
notable exception. This commit adds the LOG_PATCH options that acts as
the other LOG_* options.

Auxiliary/vim/syntax/cmake.vim

@@ -877,6 +877,7 @@ syn keyword cmakeKWExternalProject contained
             \ LOG_DOWNLOAD
             \ LOG_INSTALL
             \ LOG_MERGED_STDOUTERR
+            \ LOG_PATCH
             \ LOG_TEST
             \ LOG_UPDATE
             \ MAKE_EXE

Help/release/dev/ExternalProject-log-options.rst

@@ -3,3 +3,6 @@ ExternalProject-log-options
 
 * The :module:`ExternalProject` module :command:`ExternalProject_Add` command
   gained ``LOG_DIR`` and ``LOG_MERGED_STDOUTERR`` options to control logging.
+
+* The :module:`ExternalProject` module :command:`ExternalProject_Add` command
+  gained ``LOG_PATCH`` to optionally log the patch step.

Modules/ExternalProject.cmake

@@ -532,6 +532,9 @@ External Project Definition
     ``LOG_UPDATE <bool>``
       When enabled, the output of the update step is logged to files.
 
+    ``LOG_PATCH <bool>``
+      When enabled, the output of the patch step is logged to files.
+
     ``LOG_CONFIGURE <bool>``
       When enabled, the output of the configure step is logged to files.
 
@@ -2760,10 +2763,18 @@ function(_ep_add_patch_command name)
     set(work_dir ${source_dir})
   endif()
 
+  get_property(log TARGET ${name} PROPERTY _EP_LOG_PATCH)
+  if(log)
+    set(log LOG 1)
+  else()
+    set(log "")
+  endif()
+
   ExternalProject_Add_Step(${name} patch
     COMMAND ${cmd}
     WORKING_DIRECTORY ${work_dir}
     DEPENDEES download
+    ${log}
     )
 endfunction()
 

Tests/ExternalProjectLocal/CMakeLists.txt

@@ -100,6 +100,7 @@ ExternalProject_Add(${proj}
              -DTEST_LIST:STRING=A::B::C
   INSTALL_COMMAND ""
   LOG_CONFIGURE 1
+  LOG_PATCH 1
 )
 set_property(TARGET ${proj} PROPERTY FOLDER "Local/TAR")