Merge branch 'backport-3.16-pch-fix-bad-ClearSourcesCache' into release-3.16

Merge-request: !4815

Source/cmGeneratorTarget.cxx

@@ -3496,8 +3496,6 @@ std::string cmGeneratorTarget::GetPchFileObject(const std::string& config,
     }
     std::string& filename = inserted.first->second;
 
-    this->AddSource(pchSource, true);
-
     auto pchSf = this->Makefile->GetOrCreateSource(
       pchSource, false, cmSourceFileLocationKind::Known);
 

Source/cmGlobalGenerator.cxx

@@ -1564,7 +1564,23 @@ bool cmGlobalGenerator::AddAutomaticSources()
         continue;
       }
       lg->AddUnityBuild(gt);
-      lg->AddPchDependencies(gt);
+      // Targets that re-use a PCH are handled below.
+      if (!gt->GetProperty("PRECOMPILE_HEADERS_REUSE_FROM")) {
+        lg->AddPchDependencies(gt);
+      }
+    }
+  }
+  for (cmLocalGenerator* lg : this->LocalGenerators) {
+    for (cmGeneratorTarget* gt : lg->GetGeneratorTargets()) {
+      if (gt->GetType() == cmStateEnums::INTERFACE_LIBRARY ||
+          gt->GetType() == cmStateEnums::UTILITY ||
+          gt->GetType() == cmStateEnums::GLOBAL_TARGET) {
+        continue;
+      }
+      // Handle targets that re-use a PCH from an above-handled target.
+      if (gt->GetProperty("PRECOMPILE_HEADERS_REUSE_FROM")) {
+        lg->AddPchDependencies(gt);
+      }
     }
   }
   // The above transformations may have changed the classification of sources.

Tests/RunCMake/PrecompileHeaders/PchReuseFrom.cmake

@@ -5,6 +5,11 @@ if(CMAKE_C_COMPILE_OPTIONS_USE_PCH)
   add_definitions(-DHAVE_PCH_SUPPORT)
 endif()
 
+# Add this before the target from which we will reuse the PCH
+# to test that generators can handle reversed ordering.
+add_library(foo foo.c)
+target_include_directories(foo PUBLIC include)
+
 add_library(empty empty.c)
 target_precompile_headers(empty PRIVATE
   <stdio.h>
@@ -12,8 +17,6 @@ target_precompile_headers(empty PRIVATE
 )
 target_include_directories(empty PUBLIC include)
 
-add_library(foo foo.c)
-target_include_directories(foo PUBLIC include)
 target_precompile_headers(foo REUSE_FROM empty)
 
 # should not cause problems if configured multiple times