VS: Add policy to build custom commands concurrently

In commit 33c15ae2b9 (VS: Build custom commands concurrently when
possible, 2023-01-19, v3.26.0-rc1~56^2) we added `BuildInParallel` to
custom commands in `.vcxproj` files, but that had to be reverted by
commit abb1c12162 (VS: Revert "Build custom commands concurrently when
possible", 2023-03-07, v3.26.0-rc6~3^2) because some projects may have
custom commands that accidentally rely on serial execution in MSBuild.

Add a policy to use `BuildInParallel` for custom commands in projects
that have been updated to set the policy to `NEW`.

Fixes: #18405

3 files changed, 48 insertions, 0 deletions

diff --git a/Tests/RunCMake/VS10Project/CustomCommandParallel-check.cmake b/Tests/RunCMake/VS10Project/CustomCommandParallel-check.cmake
new file mode 100644
index 0000000..87e2f70
--- /dev/null
+++ b/Tests/RunCMake/VS10Project/CustomCommandParallel-check.cmake
@@ -0,0 +1,40 @@
+set(vcProjectFile "${RunCMake_TEST_BINARY_DIR}/foo.vcxproj")
+if(NOT EXISTS "${vcProjectFile}")
+  set(RunCMake_TEST_FAILED "Project file ${vcProjectFile} does not exist.")
+  return()
+endif()
+
+set(found_CustomBuild_cmp0147_new 0)
+set(found_CustomBuild_cmp0147_old 0)
+set(found_BuildInParallel_cmp0147_new 0)
+set(found_BuildInParallel_cmp0147_old 0)
+set(in_CustomBuild_cmp0147 "")
+file(STRINGS "${vcProjectFile}" lines)
+foreach(line IN LISTS lines)
+  if(line MATCHES [[<CustomBuild Include=".*\\cmp0147-old\.txt\.rule">]])
+    set(found_CustomBuild_cmp0147_old 1)
+    set(in_CustomBuild_cmp0147 "old")
+  endif()
+  if(line MATCHES [[<CustomBuild Include=".*\\cmp0147-new\.txt\.rule">]])
+    set(found_CustomBuild_cmp0147_new 1)
+    set(in_CustomBuild_cmp0147 "new")
+  endif()
+  if(line MATCHES [[</CustomBuild>]])
+    set(in_CustomBuild_cmp0147 "")
+  endif()
+  if(line MATCHES [[<BuildInParallel .*>true</BuildInParallel>]] AND in_CustomBuild_cmp0147)
+    set(found_BuildInParallel_cmp0147_${in_CustomBuild_cmp0147} 1)
+  endif()
+endforeach()
+if(NOT found_CustomBuild_cmp0147_new)
+  string(APPEND RunCMake_TEST_FAILED "CustomBuild for cmp0147-new.txt.rule not found in\n  ${vcProjectFile}\n")
+endif()
+if(NOT found_CustomBuild_cmp0147_old)
+  string(APPEND RunCMake_TEST_FAILED "CustomBuild for cmp0147-old.txt.rule not found in\n  ${vcProjectFile}\n")
+endif()
+if(NOT found_BuildInParallel_cmp0147_new)
+  string(APPEND RunCMake_TEST_FAILED "BuildInParallel for cmp0147-new.txt.rule not found in\n  ${vcProjectFile}\n")
+endif()
+if(found_BuildInParallel_cmp0147_old)
+  string(APPEND RunCMake_TEST_FAILED "BuildInParallel for cmp0147-old.txt.rule incorrectly found in\n  ${vcProjectFile}\n")
+endif()
diff --git a/Tests/RunCMake/VS10Project/CustomCommandParallel.cmake b/Tests/RunCMake/VS10Project/CustomCommandParallel.cmake
new file mode 100644
index 0000000..784fc68
--- /dev/null
+++ b/Tests/RunCMake/VS10Project/CustomCommandParallel.cmake
@@ -0,0 +1,5 @@
+cmake_policy(VERSION 3.26) # CMP0147 left unset
+add_custom_command(OUTPUT "cmp0147-old.txt" COMMAND echo)
+cmake_policy(SET CMP0147 NEW)
+add_custom_command(OUTPUT "cmp0147-new.txt" COMMAND echo)
+add_custom_target(foo DEPENDS "cmp0147-old.txt" "cmp0147-new.txt")
diff --git a/Tests/RunCMake/VS10Project/RunCMakeTest.cmake b/Tests/RunCMake/VS10Project/RunCMakeTest.cmake
index ed74896..669049a 100644
--- a/Tests/RunCMake/VS10Project/RunCMakeTest.cmake
+++ b/Tests/RunCMake/VS10Project/RunCMakeTest.cmake
@@ -8,6 +8,9 @@ if(CMAKE_C_COMPILER_ID STREQUAL "MSVC" AND CMAKE_C_COMPILER_VERSION VERSION_GREA
 endif()
 
 run_cmake(CustomCommandGenex)
+if(NOT RunCMake_GENERATOR MATCHES "^Visual Studio 1[1-5] ")
+  run_cmake(CustomCommandParallel)
+endif()
 run_cmake(VsCsharpSourceGroup)
 run_cmake(VsCSharpCompilerOpts)
 run_cmake(ExplicitCMakeLists)