INTERFACE_LINK_LIBRARIES_DIRECT: Honor link dependencies through LINK_ONLY

In commit f3ad061858 (Add usage requirements to update direct link
dependencies, 2022-01-12, v3.23.0-rc1~44^2), we evaluated the transitive
closure of `INTERFACE_LINK_LIBRARIES` as a non-linking usage requirement.
That left out `INTERFACE_LINK_LIBRARIES_DIRECT` link dependencies that
appear behind private dependencies of a static library, guarded by the
`$<LINK_ONLY:...>` generator expression.  At the time, that decision was
intentional, in order to prevent arbitrary usage requirements from
leaking out of `PRIVATE` dependencies.

Since then, we've revised evaluation of `LINK_LIBRARIES` to distinguish
between collecting link dependencies and other usage requirements.  Use
that information when following `INTERFACE_LINK_LIBRARIES` to collect
the matching kind of requirements from `INTERFACE_LINK_LIBRARIES_DIRECT`.

Fixes: #22496

3 files changed, 34 insertions, 6 deletions

diff --git a/Tests/InterfaceLinkLibrariesDirect/CMakeLists.txt b/Tests/InterfaceLinkLibrariesDirect/CMakeLists.txt
index b06a2fb..dec131d 100644
--- a/Tests/InterfaceLinkLibrariesDirect/CMakeLists.txt
+++ b/Tests/InterfaceLinkLibrariesDirect/CMakeLists.txt
@@ -52,7 +52,7 @@ set_property(TARGET A APPEND PROPERTY INTERFACE_LINK_LIBRARIES_DIRECT
 add_library(static_A_public STATIC static_A_public.c)
 target_link_libraries(static_A_public PUBLIC A)
 
-# Uses A's usage requirements, but does not propagate them.
+# Uses A's usage requirements, but propagates only the linking requirements.
 # Does not use the exe-only usage requirement.  Does use the optional one.
 add_library(static_A_private STATIC static_A_private.c)
 target_link_libraries(static_A_private PRIVATE A)
@@ -63,10 +63,15 @@ add_executable(exe_use_static_A_public exe_use_static_A_public.c)
 target_link_libraries(exe_use_static_A_public PRIVATE static_A_public)
 set_property(TARGET exe_use_static_A_public PROPERTY A_LINK_OPTIONAL 1)
 
-# Does not use A's usage requirements.
+# Does not use A's usage requirements, but does use its non-optional linking requirements.
 add_executable(exe_use_static_A_private exe_use_static_A_private.c)
 target_link_libraries(exe_use_static_A_private PRIVATE static_A_private)
 
+# Uses A's usage requirements, including an optional one, but overrides the link ordering.
+add_executable(exe_use_static_A_public_explicit exe_use_static_A_public_explicit.c)
+target_link_libraries(exe_use_static_A_public_explicit PRIVATE static_A_public A direct_from_A direct_from_A_for_exe direct_from_A_optional)
+set_property(TARGET exe_use_static_A_public_explicit PROPERTY A_LINK_OPTIONAL 1)
+
 #----------------------------------------------------------------------------
 
 # Test how original and injected dependencies get ordered.
diff --git a/Tests/InterfaceLinkLibrariesDirect/exe_use_static_A_private.c b/Tests/InterfaceLinkLibrariesDirect/exe_use_static_A_private.c
index 024e96e..12cf309 100644
--- a/Tests/InterfaceLinkLibrariesDirect/exe_use_static_A_private.c
+++ b/Tests/InterfaceLinkLibrariesDirect/exe_use_static_A_private.c
@@ -9,15 +9,15 @@
 #endif
 
 extern void static_A_private(void);
-extern void not_direct_from_A(void);
-extern void not_direct_from_A_for_exe(void);
+extern void direct_from_A(void);
+extern void direct_from_A_for_exe(void);
 extern void not_direct_from_A_optional(void);
 
 int main(void)
 {
   static_A_private();
-  not_direct_from_A();
-  not_direct_from_A_for_exe();
+  direct_from_A();
+  direct_from_A_for_exe();
   not_direct_from_A_optional();
   return 0;
 }
diff --git a/Tests/InterfaceLinkLibrariesDirect/exe_use_static_A_public_explicit.c b/Tests/InterfaceLinkLibrariesDirect/exe_use_static_A_public_explicit.c
new file mode 100644
index 0000000..f698a24
--- /dev/null
+++ b/Tests/InterfaceLinkLibrariesDirect/exe_use_static_A_public_explicit.c
@@ -0,0 +1,23 @@
+#ifndef DEF_DIRECT_FROM_A
+#  error "DEF_DIRECT_FROM_A incorrectly not defined"
+#endif
+#ifndef DEF_DIRECT_FROM_A_FOR_EXE
+#  error "DEF_DIRECT_FROM_A_FOR_EXE incorrectly not defined"
+#endif
+#ifndef DEF_DIRECT_FROM_A_OPTIONAL
+#  error "DEF_DIRECT_FROM_A_OPTIONAL incorrectly not defined"
+#endif
+
+extern void static_A_public(void);
+extern void not_direct_from_A(void);
+extern void not_direct_from_A_for_exe(void);
+extern void not_direct_from_A_optional(void);
+
+int main(void)
+{
+  static_A_public();
+  not_direct_from_A();
+  not_direct_from_A_for_exe();
+  not_direct_from_A_optional();
+  return 0;
+}