Ninja: Always re-run custom commands that have symbolic dependencies

If a custom command has a SYMBOLIC output (that is never actually
created) then do not mark the custom command build statement as
'restat'.  Otherwise other custom commands that depend on the symbolic
output may not always re-run because after running the first custom
command Ninja 'restat' will detect that the output timestamp did not
change and skip its dependents.

This was observed with the ExternalProject BUILD_ALWAYS option where
Ninja would not re-run the 'install' step each time 'build' re-runs.

3 files changed, 37 insertions, 1 deletions

diff --git a/Source/cmLocalNinjaGenerator.cxx b/Source/cmLocalNinjaGenerator.cxx
index d9517d8..b2927a9 100644
--- a/Source/cmLocalNinjaGenerator.cxx
+++ b/Source/cmLocalNinjaGenerator.cxx
@@ -398,6 +398,16 @@ cmLocalNinjaGenerator::WriteCustomCommandBuildStatement(
   const std::vector<std::string> &byproducts = ccg.GetByproducts();
   cmNinjaDeps ninjaOutputs(outputs.size()+byproducts.size()), ninjaDeps;
 
+  bool symbolic = false;
+  for (std::vector<std::string>::const_iterator o = outputs.begin();
+       o != outputs.end(); ++o)
+    {
+    if (cmSourceFile* sf = this->Makefile->GetSource(*o))
+      {
+      symbolic = sf->GetPropertyAsBool("SYMBOLIC");
+      }
+    }
+
 #if 0
 #error TODO: Once CC in an ExternalProject target must provide the \
     file of each imported target that has an add_dependencies pointing \
@@ -434,7 +444,7 @@ cmLocalNinjaGenerator::WriteCustomCommandBuildStatement(
       this->ConstructComment(ccg),
       "Custom command for " + ninjaOutputs[0],
       cc->GetUsesTerminal(),
-      /*restat*/true,
+      /*restat*/!symbolic,
       ninjaOutputs,
       ninjaDeps,
       orderOnlyDeps);
diff --git a/Tests/RunCMake/BuildDepends/Custom-Always.cmake b/Tests/RunCMake/BuildDepends/Custom-Always.cmake
new file mode 100644
index 0000000..d412708
--- /dev/null
+++ b/Tests/RunCMake/BuildDepends/Custom-Always.cmake
@@ -0,0 +1,24 @@
+add_custom_command(
+  OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/before-always
+  COMMAND ${CMAKE_COMMAND} -E touch before-always
+  )
+add_custom_command(
+  OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/always
+  COMMAND ${CMAKE_COMMAND} -E touch always-updated
+  DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/before-always
+  )
+set_property(SOURCE always PROPERTY SYMBOLIC 1)
+add_custom_command(
+  OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/after-always
+  DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/always
+  COMMAND ${CMAKE_COMMAND} -E touch after-always
+  )
+
+add_custom_target(drive ALL DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/after-always)
+
+file(GENERATE OUTPUT check-$<LOWER_CASE:$<CONFIG>>.cmake CONTENT "
+set(check_pairs
+  \"${CMAKE_CURRENT_BINARY_DIR}/always-updated|${CMAKE_CURRENT_BINARY_DIR}/before-always\"
+  \"${CMAKE_CURRENT_BINARY_DIR}/after-always|${CMAKE_CURRENT_BINARY_DIR}/always-updated\"
+  )
+")
diff --git a/Tests/RunCMake/BuildDepends/RunCMakeTest.cmake b/Tests/RunCMake/BuildDepends/RunCMakeTest.cmake
index a578408..31c72fb 100644
--- a/Tests/RunCMake/BuildDepends/RunCMakeTest.cmake
+++ b/Tests/RunCMake/BuildDepends/RunCMakeTest.cmake
@@ -38,3 +38,5 @@ if(NOT RunCMake_GENERATOR MATCHES "Visual Studio [67]|Xcode")
   run_BuildDepends(C-Exe-Manifest)
   unset(run_BuildDepends_skip_step_2)
 endif()
+
+run_BuildDepends(Custom-Always)