pchreuse: defer dependency addition until generation time

Note that this does lose the backtrace information. It also, however,
makes `PRECOMPILE_HEADERS_REUSE_FROM` a non-magic property now.
Previously, appending to the property would miss all of its behaviors
(or leave existing setup in-place which is no longer relevant
post-append). Rather than making a policy to block appending, just defer
all logic to generation time.

Source/cmGeneratorTarget.cxx

@@ -1008,6 +1008,10 @@ std::set<cmLinkItem> const& cmGeneratorTarget::GetUtilityItems() const
           cmLinkItem(i.Value.first, i.Value.second, i.Backtrace));
       }
     }
+    if (cmGeneratorTarget const* reuseTarget = this->GetPchReuseTarget()) {
+      this->UtilityItems.insert(
+        cmLinkItem(reuseTarget, false, cmListFileBacktrace()));
+    }
   }
   return this->UtilityItems;
 }

Source/cmTarget.cxx

@@ -1911,7 +1911,6 @@ MAKE_PROP(COMPILE_DEFINITIONS);
 MAKE_PROP(COMPILE_FEATURES);
 MAKE_PROP(COMPILE_OPTIONS);
 MAKE_PROP(PRECOMPILE_HEADERS);
-MAKE_PROP(PRECOMPILE_HEADERS_REUSE_FROM);
 MAKE_PROP(CUDA_CUBIN_COMPILATION);
 MAKE_PROP(CUDA_FATBIN_COMPILATION);
 MAKE_PROP(CUDA_OPTIX_COMPILATION);
@@ -2147,11 +2146,6 @@ void cmTarget::SetProperty(std::string const& prop, cmValue value)
       this->impl->Makefile->IssueMessage(MessageType::FATAL_ERROR, e);
       return;
     }
-  } else if (prop == propPRECOMPILE_HEADERS_REUSE_FROM) {
-    this->impl->Properties.SetProperty(prop, value);
-    if (value) {
-      this->AddUtility(*value, false, this->impl->Makefile);
-    }
   } else if (prop == propC_STANDARD || prop == propCXX_STANDARD ||
              prop == propCUDA_STANDARD || prop == propHIP_STANDARD ||
              prop == propOBJC_STANDARD || prop == propOBJCXX_STANDARD) {

Tests/RunCMake/PrecompileHeaders/PchReuseAppend-build-stderr.txt

@@ -0,0 +1,2 @@
+((Classic Intel)?Warning #672: the command line options do not match those used[^
+]*)?

Tests/RunCMake/PrecompileHeaders/PchReuseAppend.cmake

@@ -0,0 +1,60 @@
+enable_language(CXX)
+
+if(CMAKE_CXX_COMPILE_OPTIONS_USE_PCH)
+  add_definitions(-DHAVE_PCH_SUPPORT)
+endif()
+
+######################################################################
+
+file(WRITE ${CMAKE_BINARY_DIR}/pch.cxx [=[
+void nothing()
+{
+}
+]=])
+
+file(WRITE ${CMAKE_BINARY_DIR}/string.hxx [=[
+#include <string.h>
+
+namespace std {
+  struct string
+  {
+    char storage[20];
+
+    string(const char* s) {
+      strcpy(storage, s);
+    }
+
+    const char* c_str() const {
+      return storage;
+    }
+  };
+}
+]=])
+
+add_library(pch-generator ${CMAKE_BINARY_DIR}/pch.cxx)
+target_precompile_headers(pch-generator PRIVATE ${CMAKE_BINARY_DIR}/string.hxx)
+
+######################################################################
+
+file(WRITE ${CMAKE_BINARY_DIR}/message.cxx [=[
+#include "message.hxx"
+
+#ifndef HAVE_PCH_SUPPORT
+  #include "string.hxx"
+#endif
+
+const char* message()
+{
+  static std::string greeting("hi there");
+  return greeting.c_str();
+}
+]=])
+
+file(WRITE ${CMAKE_BINARY_DIR}/message.hxx [=[
+const char* message();
+]=])
+
+add_library(reuse_append ${CMAKE_BINARY_DIR}/message.cxx)
+target_include_directories(reuse_append PRIVATE ${CMAKE_BINARY_DIR})
+set_property(TARGET reuse_append PROPERTY PRECOMPILE_HEADERS_REUSE_FROM "pch-")
+set_property(TARGET reuse_append APPEND_STRING PROPERTY PRECOMPILE_HEADERS_REUSE_FROM "generator")

Tests/RunCMake/PrecompileHeaders/RunCMakeTest.cmake

@@ -34,6 +34,7 @@ run_build_verbose(PchReuseFromUseUpdatedProps)
 run_build_verbose(PchReuseConsistency)
 run_cmake(PchReuseFromCycle)
 run_cmake(PchReuseWithoutPch)
+run_build_verbose(PchReuseAppend)
 run_cmake(PchMultilanguage)
 run_build_verbose(PchReuseDeclarationOrder)
 if(RunCMake_GENERATOR MATCHES "Make|Ninja")