objlib: Allow other libraries to link to `OBJECT` libraries.

Note: This only allows `OBJECT` libraries to be on the right-hand side
of `target_link_libraries` but still does not link its object-files to
the target on the left-hand side.

Issue: #14778

13 files changed, 67 insertions, 28 deletions

diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHS1-result.txt b/Tests/RunCMake/ObjectLibrary/LinkObjRHS1-result.txt
deleted file mode 100644
index d00491f..0000000
--- a/Tests/RunCMake/ObjectLibrary/LinkObjRHS1-result.txt
+++ /dev/null
@@ -1 +0,0 @@
-1
diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHS1-stderr.txt b/Tests/RunCMake/ObjectLibrary/LinkObjRHS1-stderr.txt
deleted file mode 100644
index d5ee4f9..0000000
--- a/Tests/RunCMake/ObjectLibrary/LinkObjRHS1-stderr.txt
+++ /dev/null
@@ -1,6 +0,0 @@
-CMake Error at LinkObjRHS1.cmake:3 \(target_link_libraries\):
-  Target "AnObjLib" of type OBJECT_LIBRARY may not be linked into another
-  target.  One may link only to INTERFACE, STATIC or SHARED libraries, or to
-  executables with the ENABLE_EXPORTS property set.
-Call Stack \(most recent call first\):
-  CMakeLists.txt:3 \(include\)
diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHS1.cmake b/Tests/RunCMake/ObjectLibrary/LinkObjRHS1.cmake
deleted file mode 100644
index 113d6a8..0000000
--- a/Tests/RunCMake/ObjectLibrary/LinkObjRHS1.cmake
+++ /dev/null
@@ -1,3 +0,0 @@
-add_library(A STATIC a.c)
-add_library(AnObjLib OBJECT a.c)
-target_link_libraries(A AnObjLib)
diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHS2-result.txt b/Tests/RunCMake/ObjectLibrary/LinkObjRHS2-result.txt
deleted file mode 100644
index d00491f..0000000
--- a/Tests/RunCMake/ObjectLibrary/LinkObjRHS2-result.txt
+++ /dev/null
@@ -1 +0,0 @@
-1
diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHS2-stderr.txt b/Tests/RunCMake/ObjectLibrary/LinkObjRHS2-stderr.txt
deleted file mode 100644
index 3295fca..0000000
--- a/Tests/RunCMake/ObjectLibrary/LinkObjRHS2-stderr.txt
+++ /dev/null
@@ -1,6 +0,0 @@
-CMake Error at LinkObjRHS2.cmake:1 \(add_library\):
-  Target "A" links to OBJECT library "AnObjLib" but this is not allowed.  One
-  may link only to STATIC or SHARED libraries, or to executables with the
-  ENABLE_EXPORTS property set.
-Call Stack \(most recent call first\):
-  CMakeLists.txt:3 \(include\)
diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHS2.cmake b/Tests/RunCMake/ObjectLibrary/LinkObjRHS2.cmake
deleted file mode 100644
index 6163729..0000000
--- a/Tests/RunCMake/ObjectLibrary/LinkObjRHS2.cmake
+++ /dev/null
@@ -1,3 +0,0 @@
-add_library(A SHARED a.c)
-target_link_libraries(A AnObjLib)
-add_library(AnObjLib OBJECT a.c)
diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHSShared.cmake b/Tests/RunCMake/ObjectLibrary/LinkObjRHSShared.cmake
new file mode 100644
index 0000000..b9030b3
--- /dev/null
+++ b/Tests/RunCMake/ObjectLibrary/LinkObjRHSShared.cmake
@@ -0,0 +1,13 @@
+enable_language(C)
+
+add_definitions(-DCOMPILE_FOR_SHARED_LIB)
+
+add_library(AnObjLib OBJECT a.c)
+target_compile_definitions(AnObjLib INTERFACE REQUIRED)
+set_target_properties(AnObjLib PROPERTIES POSITION_INDEPENDENT_CODE ON)
+
+add_library(A SHARED b.c $<TARGET_OBJECTS:AnObjLib>)
+target_link_libraries(A PUBLIC AnObjLib)
+
+add_executable(exe exe.c)
+target_link_libraries(exe A)
diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHSStatic.cmake b/Tests/RunCMake/ObjectLibrary/LinkObjRHSStatic.cmake
new file mode 100644
index 0000000..73fad06
--- /dev/null
+++ b/Tests/RunCMake/ObjectLibrary/LinkObjRHSStatic.cmake
@@ -0,0 +1,10 @@
+enable_language(C)
+
+add_library(AnObjLib OBJECT a.c)
+target_compile_definitions(AnObjLib INTERFACE REQUIRED)
+
+add_library(A STATIC b.c $<TARGET_OBJECTS:AnObjLib>)
+target_link_libraries(A PUBLIC AnObjLib)
+
+add_executable(exe exe.c)
+target_link_libraries(exe A)
diff --git a/Tests/RunCMake/ObjectLibrary/ObjWithObj-stderr.txt b/Tests/RunCMake/ObjectLibrary/ObjWithObj-stderr.txt
index d67b4ae..aadc5e0 100644
--- a/Tests/RunCMake/ObjectLibrary/ObjWithObj-stderr.txt
+++ b/Tests/RunCMake/ObjectLibrary/ObjWithObj-stderr.txt
@@ -1,4 +1,10 @@
-CMake Error at ObjWithObj.cmake:2 \(add_library\):
-  Only executables and non-OBJECT libraries may reference target objects.
+^CMake Error at ObjWithObj.cmake:[0-9]+ \(add_library\):
+  OBJECT library \"B\" contains:
+
+    [^
+]*a(\.c)?\.o(bj)?
+
+  but may contain only sources that compile, header files, and other files
+  that would not affect linking of a normal library.
 Call Stack \(most recent call first\):
-  CMakeLists.txt:3 \(include\)
+  CMakeLists.txt:[0-9]+ \(include\)$
diff --git a/Tests/RunCMake/ObjectLibrary/RunCMakeTest.cmake b/Tests/RunCMake/ObjectLibrary/RunCMakeTest.cmake
index 1660779..6724da1 100644
--- a/Tests/RunCMake/ObjectLibrary/RunCMakeTest.cmake
+++ b/Tests/RunCMake/ObjectLibrary/RunCMakeTest.cmake
@@ -26,9 +26,9 @@ endfunction ()
 
 run_object_lib_build(LinkObjLHSShared)
 run_object_lib_build(LinkObjLHSStatic)
+run_object_lib_build(LinkObjRHSShared)
+run_object_lib_build(LinkObjRHSStatic)
 
-run_cmake(LinkObjRHS1)
-run_cmake(LinkObjRHS2)
 run_cmake(MissingSource)
 run_cmake(ObjWithObj)
 run_cmake(OwnSources)
diff --git a/Tests/RunCMake/ObjectLibrary/a.c b/Tests/RunCMake/ObjectLibrary/a.c
index 1636303..5beb3f1 100644
--- a/Tests/RunCMake/ObjectLibrary/a.c
+++ b/Tests/RunCMake/ObjectLibrary/a.c
@@ -1,4 +1,10 @@
-int a(void)
+#if defined(_WIN32) && defined(COMPILE_FOR_SHARED_LIB)
+#define EXPORT __declspec(dllexport)
+#else
+#define EXPORT
+#endif
+
+EXPORT int a(void)
 {
   return 0;
 }
diff --git a/Tests/RunCMake/ObjectLibrary/b.c b/Tests/RunCMake/ObjectLibrary/b.c
index 6751907..7549abf 100644
--- a/Tests/RunCMake/ObjectLibrary/b.c
+++ b/Tests/RunCMake/ObjectLibrary/b.c
@@ -1,4 +1,14 @@
-int b(void)
+#if defined(_WIN32) && defined(COMPILE_FOR_SHARED_LIB)
+#define EXPORT __declspec(dllexport)
+#else
+#define EXPORT
+#endif
+
+extern int a(void);
+EXPORT int b()
 {
-  return 0;
+  return a();
 }
+#ifndef REQUIRED
+#error "REQUIRED needs to be defined"
+#endif
diff --git a/Tests/RunCMake/ObjectLibrary/exe.c b/Tests/RunCMake/ObjectLibrary/exe.c
new file mode 100644
index 0000000..6efdae7
--- /dev/null
+++ b/Tests/RunCMake/ObjectLibrary/exe.c
@@ -0,0 +1,14 @@
+#if defined(_WIN32) && defined(COMPILE_FOR_SHARED_LIB)
+#define IMPORT __declspec(dllimport)
+#else
+#define IMPORT
+#endif
+
+extern IMPORT int b(void);
+int main()
+{
+  return b();
+}
+#ifndef REQUIRED
+#error "REQUIRED needs to be defined"
+#endif