target_link_libraries: Optionally require only target names

Optionally verify that items in `LINK_LIBRARIES` and
`INTERFACE_LINK_LIBRARIES` that can be target names are actually target
names.  Add a `LINK_LIBRARIES_ONLY_TARGETS` target property and
corresponding `CMAKE_LINK_LIBRARIES_ONLY_TARGETS` variable to enable
this new check.

Fixes: #22858

6 files changed, 106 insertions, 0 deletions

diff --git a/Tests/RunCMake/LinkItemValidation/CMakeLists.txt b/Tests/RunCMake/LinkItemValidation/CMakeLists.txt
index 4f867df..185cd91 100644
--- a/Tests/RunCMake/LinkItemValidation/CMakeLists.txt
+++ b/Tests/RunCMake/LinkItemValidation/CMakeLists.txt
@@ -1,3 +1,6 @@
 cmake_minimum_required(VERSION 2.8.12)
+if(NOT RunCMake_TEST MATCHES "^CMP0028")
+  cmake_minimum_required(VERSION 3.22)
+endif()
 project(${RunCMake_TEST} CXX)
 include(${RunCMake_TEST}.cmake NO_POLICY_SCOPE) # policy used at end of dir
diff --git a/Tests/RunCMake/LinkItemValidation/OnlyTargets-result.txt b/Tests/RunCMake/LinkItemValidation/OnlyTargets-result.txt
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/Tests/RunCMake/LinkItemValidation/OnlyTargets-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/LinkItemValidation/OnlyTargets-stderr.txt b/Tests/RunCMake/LinkItemValidation/OnlyTargets-stderr.txt
new file mode 100644
index 0000000..bbb0170
--- /dev/null
+++ b/Tests/RunCMake/LinkItemValidation/OnlyTargets-stderr.txt
@@ -0,0 +1,40 @@
+^CMake Error at OnlyTargets\.cmake:11 \(target_link_libraries\):
+  Target "exe" has LINK_LIBRARIES_ONLY_TARGETS enabled, but it links to:
+
+    non_target_in_exe
+
+  which is not a target\.  Possible reasons include:
+(
+    \*[^
+]+)*
+
+Call Stack \(most recent call first\):
+  CMakeLists\.txt:[0-9]+ \(include\)
++
+CMake Error at OnlyTargets\.cmake:21 \(target_link_libraries\):
+  Target "iface" has LINK_LIBRARIES_ONLY_TARGETS enabled, but its link
+  interface contains:
+
+    non_target_in_iface
+
+  which is not a target\.  Possible reasons include:
+(
+    \*[^
+]+)*
+
+Call Stack \(most recent call first\):
+  CMakeLists\.txt:[0-9]+ \(include\)
++
+CMake Error at OnlyTargets\.cmake:30 \(target_link_libraries\):
+  Target "iface_imported_checked" has LINK_LIBRARIES_ONLY_TARGETS enabled,
+  but its link interface contains:
+
+    non_target_in_iface_imported_checked
+
+  which is not a target\.  Possible reasons include:
+(
+    \*[^
+]+)*
+
+Call Stack \(most recent call first\):
+  CMakeLists\.txt:[0-9]+ \(include\)
diff --git a/Tests/RunCMake/LinkItemValidation/OnlyTargets.cmake b/Tests/RunCMake/LinkItemValidation/OnlyTargets.cmake
new file mode 100644
index 0000000..9417318
--- /dev/null
+++ b/Tests/RunCMake/LinkItemValidation/OnlyTargets.cmake
@@ -0,0 +1,56 @@
+enable_language(C)
+
+set(CMAKE_LINK_LIBRARIES_ONLY_TARGETS 1)
+
+# Use imported interface library to name toolchain-provided libraries.
+add_library(toolchain::m INTERFACE IMPORTED)
+set_property(TARGET toolchain::m PROPERTY IMPORTED_LIBNAME "m")
+
+# Linking directly warns.
+add_executable(exe main.c)
+target_link_libraries(exe PRIVATE
+  -lflag_in_exe     # accepted
+  /abs/path/in_exe  # accepted
+  rel/path/in_exe   # accepted
+  toolchain::m      # accepted
+  non_target_in_exe # rejected
+  )
+
+# Link interfaces warn.
+add_library(iface INTERFACE)
+target_link_libraries(iface INTERFACE
+  -lflag_in_iface     # accepted
+  /abs/path/in_iface  # accepted
+  rel/path/in_iface   # accepted
+  non_target_in_iface # rejected
+  )
+
+# Imported target link interfaces warn if explicitly enabled.
+add_library(iface_imported_checked INTERFACE IMPORTED)
+target_link_libraries(iface_imported_checked INTERFACE
+  -lflag_iface_imported_checked        # accepted
+  /abs/path/in_iface_imported_checked  # accepted
+  rel/path/in_iface_imported_checked   # accepted
+  non_target_in_iface_imported_checked # rejected
+  )
+set_property(TARGET iface_imported_checked PROPERTY LINK_LIBRARIES_ONLY_TARGETS 1)
+
+# Linking directly does not warn if explicitly disabled.
+add_executable(exe_not_checked main.c)
+target_link_libraries(exe_not_checked PRIVATE
+  non_target_in_exe_not_checked
+  )
+set_property(TARGET exe_not_checked PROPERTY LINK_LIBRARIES_ONLY_TARGETS 0)
+
+# Link interfaces do not warn if explicitly disabled.
+add_library(iface_not_checked INTERFACE)
+target_link_libraries(iface_not_checked INTERFACE
+  non_target_in_iface_not_checked
+  )
+set_property(TARGET iface_not_checked PROPERTY LINK_LIBRARIES_ONLY_TARGETS 0)
+
+# Imported target link interfaces do not warn if not explicitly enabled.
+add_library(iface_imported_default INTERFACE IMPORTED)
+target_link_libraries(iface_imported_default INTERFACE
+  non_target_in_iface_imported_default
+  )
diff --git a/Tests/RunCMake/LinkItemValidation/RunCMakeTest.cmake b/Tests/RunCMake/LinkItemValidation/RunCMakeTest.cmake
index 0c72ca2..c423f6a 100644
--- a/Tests/RunCMake/LinkItemValidation/RunCMakeTest.cmake
+++ b/Tests/RunCMake/LinkItemValidation/RunCMakeTest.cmake
@@ -6,3 +6,5 @@ run_cmake(CMP0028-WARN)
 run_cmake(CMP0028-NEW-iface)
 run_cmake(CMP0028-OLD-iface)
 run_cmake(CMP0028-WARN-iface)
+
+run_cmake(OnlyTargets)
diff --git a/Tests/RunCMake/LinkItemValidation/main.c b/Tests/RunCMake/LinkItemValidation/main.c
new file mode 100644
index 0000000..8488f4e
--- /dev/null
+++ b/Tests/RunCMake/LinkItemValidation/main.c
@@ -0,0 +1,4 @@
+int main(void)
+{
+  return 0;
+}