Unity: Proper handling of object libraries

Fixes: #20051

Source/cmGlobalGenerator.cxx

@@ -1567,6 +1567,15 @@ bool cmGlobalGenerator::AddAutomaticSources()
       lg->AddPchDependencies(gt);
     }
   }
+  // The above transformations may have changed the classification of sources.
+  // Clear the source list and classification cache (KindedSources) of all
+  // targets so that it will be recomputed correctly by the generators later
+  // now that the above transformations are done for all targets.
+  for (cmLocalGenerator* lg : this->LocalGenerators) {
+    for (cmGeneratorTarget* gt : lg->GetGeneratorTargets()) {
+      gt->ClearSourcesCache();
+    }
+  }
   return true;
 }
 

Source/cmLocalGenerator.cxx

@@ -2307,6 +2307,7 @@ void cmLocalGenerator::AddPchDependencies(cmGeneratorTarget* target)
   }
   const std::string buildType = cmSystemTools::UpperCase(config);
 
+  // FIXME: Refactor collection of sources to not evaluate object libraries.
   std::vector<cmSourceFile*> sources;
   target->GetSourceFiles(sources, buildType);
 
@@ -2469,6 +2470,7 @@ void cmLocalGenerator::AddUnityBuild(cmGeneratorTarget* target)
     cmStrCat(this->GetCurrentBinaryDirectory(), "/CMakeFiles/",
              target->GetName(), ".dir/Unity/");
 
+  // FIXME: Refactor collection of sources to not evaluate object libraries.
   std::vector<cmSourceFile*> sources;
   target->GetSourceFiles(sources, buildType);
 

Tests/RunCMake/ObjectLibrary/OwnSources-stderr.txt

@@ -4,4 +4,10 @@
 Call Stack \(most recent call first\):
   CMakeLists.txt:[0-9]+ \(include\)
 +
+CMake Error at OwnSources.cmake:[0-9]+ \(add_library\):
+  The SOURCES of "A" use a generator expression that depends on the SOURCES
+  themselves.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)
++
 CMake Generate step failed\.  Build files cannot be regenerated correctly\.$

Tests/RunCMake/UnityBuild/RunCMakeTest.cmake

@@ -21,3 +21,4 @@ function(run_test name)
 endfunction()
 
 run_test(unitybuild_runtest)
+run_test(unitybuild_object_library)

Tests/RunCMake/UnityBuild/unitybuild_object_library.cmake

@@ -0,0 +1,13 @@
+project(unitybuild_object_library C)
+
+set(CMAKE_UNITY_BUILD ON) # This tests that the variable works in addition to the property
+
+add_library(lib OBJECT func.c)
+
+add_library(other-lib STATIC func.c)
+
+add_executable(main main.c)
+target_link_libraries(main PRIVATE lib)
+
+enable_testing()
+add_test(NAME main COMMAND main)