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

Note: This still does not link the object-files of the `OBJECT` library
from the right-hand side of `target_link_libraries` to the target on the
left-hand side. (In this particular case of another `OBJECT` library on
the left-hand side this would not make any sense anyway. The target on
the left-hand side has no link-step.)

Issue: #14778

12 files changed, 40 insertions, 32 deletions

diff --git a/Tests/RunCMake/ObjectLibrary/BadObjSource2-result.txt b/Tests/RunCMake/ObjectLibrary/BadObjSource2-result.txt
deleted file mode 100644
index d00491f..0000000
--- a/Tests/RunCMake/ObjectLibrary/BadObjSource2-result.txt
+++ /dev/null
@@ -1 +0,0 @@
-1
diff --git a/Tests/RunCMake/ObjectLibrary/BadObjSource2-stderr.txt b/Tests/RunCMake/ObjectLibrary/BadObjSource2-stderr.txt
deleted file mode 100644
index b91ffd0..0000000
--- a/Tests/RunCMake/ObjectLibrary/BadObjSource2-stderr.txt
+++ /dev/null
@@ -1,9 +0,0 @@
-CMake Error at BadObjSource2.cmake:1 \(add_library\):
-  OBJECT library "A" contains:
-
-    bad.obj
-
-  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 \(include\)
diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject-build-result.txt b/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject-build-result.txt
new file mode 100644
index 0000000..e27f06b
--- /dev/null
+++ b/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject-build-result.txt
@@ -0,0 +1 @@
+[1-9][0-9]*
diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject-build-stdout.txt b/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject-build-stdout.txt
new file mode 100644
index 0000000..4eeb096
--- /dev/null
+++ b/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject-build-stdout.txt
@@ -0,0 +1 @@
+REQUIRED needs to be defined
diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject.cmake b/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject.cmake
new file mode 100644
index 0000000..db571a3
--- /dev/null
+++ b/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject.cmake
@@ -0,0 +1,12 @@
+cmake_policy(SET CMP0022 NEW)
+
+enable_language(C)
+
+add_library(AnObjLib OBJECT a.c)
+target_compile_definitions(AnObjLib INTERFACE REQUIRED)
+
+add_library(AnotherObjLib OBJECT b.c)
+target_link_libraries(AnotherObjLib PRIVATE AnObjLib)
+
+add_executable(exe exe.c)
+target_link_libraries(exe AnotherObjLib)
diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject2-build-result.txt b/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject2-build-result.txt
new file mode 100644
index 0000000..e27f06b
--- /dev/null
+++ b/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject2-build-result.txt
@@ -0,0 +1 @@
+[1-9][0-9]*
diff --git a/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject2.cmake b/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject2.cmake
new file mode 100644
index 0000000..6bb8d5e
--- /dev/null
+++ b/Tests/RunCMake/ObjectLibrary/LinkObjRHSObject2.cmake
@@ -0,0 +1,12 @@
+cmake_policy(SET CMP0022 NEW)
+
+enable_language(C)
+
+add_library(AnObjLib OBJECT a.c)
+target_compile_definitions(AnObjLib INTERFACE REQUIRED)
+
+add_library(AnotherObjLib OBJECT b.c)
+target_link_libraries(AnotherObjLib PUBLIC AnObjLib)
+
+add_executable(exe exe.c)
+target_link_libraries(exe AnotherObjLib)
diff --git a/Tests/RunCMake/ObjectLibrary/ObjWithObj-result.txt b/Tests/RunCMake/ObjectLibrary/ObjWithObj-result.txt
deleted file mode 100644
index d00491f..0000000
--- a/Tests/RunCMake/ObjectLibrary/ObjWithObj-result.txt
+++ /dev/null
@@ -1 +0,0 @@
-1
diff --git a/Tests/RunCMake/ObjectLibrary/ObjWithObj-stderr.txt b/Tests/RunCMake/ObjectLibrary/ObjWithObj-stderr.txt
deleted file mode 100644
index aadc5e0..0000000
--- a/Tests/RunCMake/ObjectLibrary/ObjWithObj-stderr.txt
+++ /dev/null
@@ -1,10 +0,0 @@
-^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:[0-9]+ \(include\)$
diff --git a/Tests/RunCMake/ObjectLibrary/RunCMakeTest.cmake b/Tests/RunCMake/ObjectLibrary/RunCMakeTest.cmake
index 6724da1..287331b 100644
--- a/Tests/RunCMake/ObjectLibrary/RunCMakeTest.cmake
+++ b/Tests/RunCMake/ObjectLibrary/RunCMakeTest.cmake
@@ -24,10 +24,23 @@ function (run_object_lib_build name)
   run_cmake_command(${name}-build ${CMAKE_COMMAND} --build .)
 endfunction ()
 
+function (run_object_lib_build2 name)
+  # Use a single build tree for a few tests without cleaning.
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/${name}-build)
+  set(RunCMake_TEST_NO_CLEAN 1)
+  file(REMOVE_RECURSE "${RunCMake_TEST_BINARY_DIR}")
+  file(MAKE_DIRECTORY "${RunCMake_TEST_BINARY_DIR}")
+  run_cmake(${name})
+  set(RunCMake_TEST_OUTPUT_MERGE 1)
+  run_cmake_command(${name}-build ${CMAKE_COMMAND} --build .)
+endfunction ()
+
 run_object_lib_build(LinkObjLHSShared)
 run_object_lib_build(LinkObjLHSStatic)
 run_object_lib_build(LinkObjRHSShared)
 run_object_lib_build(LinkObjRHSStatic)
+run_object_lib_build2(LinkObjRHSObject)
+run_object_lib_build2(LinkObjRHSObject2)
 
 run_cmake(MissingSource)
 run_cmake(ObjWithObj)
diff --git a/Tests/RunCMake/add_library/OBJECTwithOnlyObjectSources-result.txt b/Tests/RunCMake/add_library/OBJECTwithOnlyObjectSources-result.txt
deleted file mode 100644
index d00491f..0000000
--- a/Tests/RunCMake/add_library/OBJECTwithOnlyObjectSources-result.txt
+++ /dev/null
@@ -1 +0,0 @@
-1
diff --git a/Tests/RunCMake/add_library/OBJECTwithOnlyObjectSources-stderr.txt b/Tests/RunCMake/add_library/OBJECTwithOnlyObjectSources-stderr.txt
deleted file mode 100644
index 6183f80..0000000
--- a/Tests/RunCMake/add_library/OBJECTwithOnlyObjectSources-stderr.txt
+++ /dev/null
@@ -1,10 +0,0 @@
-^CMake Error at OBJECTwithOnlyObjectSources.cmake:[0-9]+ \(add_library\):
-  OBJECT library \"TestObjectLibWithoutSources\" contains:
-
-    [^
-]*test(\.cpp)?\.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:[0-9]+ \(include\)$