Restore support for TARGET_OBJECTS in link interfaces with unity builds

This was broken by commit df08c37a42 (cmGlobalGenerator: Add unity/pch
sources after computing compile features, 2024-02-02, v3.28.3~1^2~1^2),
and 3.28.2's commit 76b5383123 (cmGlobalGenerator: add unity sources
after computing target compile features, 2024-01-01, v3.28.2~17^2~1).

The problem is very similar to that fixed by commit 4e8f24e977 (PCH:
Clear link interface cache when adding PCH object to it, 2022-01-24,
v3.23.0-rc1~44^2~9).  Generalize that fix.

Fixes: #25696

5 files changed, 36 insertions, 0 deletions

diff --git a/Tests/RunCMake/TargetObjects/RunCMakeTest.cmake b/Tests/RunCMake/TargetObjects/RunCMakeTest.cmake
index d2b3032..9756255 100644
--- a/Tests/RunCMake/TargetObjects/RunCMakeTest.cmake
+++ b/Tests/RunCMake/TargetObjects/RunCMakeTest.cmake
@@ -6,3 +6,11 @@ run_cmake(NotObjlibTarget)
 if(RunCMake_GENERATOR STREQUAL "Xcode" AND "$ENV{CMAKE_OSX_ARCHITECTURES}" MATCHES "[;$]")
   run_cmake(XcodeVariableNoGenexExpansion)
 endif()
+
+function(run_cmake_and_build case)
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/${case}-build)
+  run_cmake(${case})
+  set(RunCMake_TEST_NO_CLEAN 1)
+  run_cmake_command(${case}-build ${CMAKE_COMMAND} --build .)
+endfunction()
+run_cmake_and_build(Unity)
diff --git a/Tests/RunCMake/TargetObjects/Unity.cmake b/Tests/RunCMake/TargetObjects/Unity.cmake
new file mode 100644
index 0000000..9c8e5c9
--- /dev/null
+++ b/Tests/RunCMake/TargetObjects/Unity.cmake
@@ -0,0 +1,13 @@
+enable_language(C)
+
+# Test transforming the set of object files provided by an object library.
+set(CMAKE_UNITY_BUILD 1)
+
+add_library(UnityObj1 OBJECT UnityObj1.c)
+add_library(UnityObj2 OBJECT UnityObj2.c)
+
+add_library(UnityObj2Iface INTERFACE)
+target_link_libraries(UnityObj2Iface INTERFACE $<TARGET_OBJECTS:UnityObj2>)
+
+add_executable(UnityMain UnityMain.c)
+target_link_libraries(UnityMain PRIVATE UnityObj1 UnityObj2Iface)
diff --git a/Tests/RunCMake/TargetObjects/UnityMain.c b/Tests/RunCMake/TargetObjects/UnityMain.c
new file mode 100644
index 0000000..9d52ef8
--- /dev/null
+++ b/Tests/RunCMake/TargetObjects/UnityMain.c
@@ -0,0 +1,7 @@
+extern int UnityObj1(void);
+extern int UnityObj2(void);
+
+int main(void)
+{
+  return UnityObj1() + UnityObj2();
+}
diff --git a/Tests/RunCMake/TargetObjects/UnityObj1.c b/Tests/RunCMake/TargetObjects/UnityObj1.c
new file mode 100644
index 0000000..ed19d14
--- /dev/null
+++ b/Tests/RunCMake/TargetObjects/UnityObj1.c
@@ -0,0 +1,4 @@
+int UnityObj1(void)
+{
+  return 0;
+}
diff --git a/Tests/RunCMake/TargetObjects/UnityObj2.c b/Tests/RunCMake/TargetObjects/UnityObj2.c
new file mode 100644
index 0000000..1cc350c
--- /dev/null
+++ b/Tests/RunCMake/TargetObjects/UnityObj2.c
@@ -0,0 +1,4 @@
+int UnityObj2(void)
+{
+  return 0;
+}