LINK_LIBRARIES: Add support for LINK_ONLY genex

Previously we always used content guarded by `$<LINK_ONLY:...>`
in `LINK_LIBRARIES`, even when evaluating for non-linking usage
requirements.  Add a policy to honor `LINK_ONLY` in `LINK_LIBRARIES`
the same way we already do in `INTERFACE_LINK_LIBRARIES`.

1 files changed, 14 insertions, 0 deletions

diff --git a/Source/cmGeneratorTarget.cxx b/Source/cmGeneratorTarget.cxx
index 6c804b5..1a13bdb 100644
--- a/Source/cmGeneratorTarget.cxx
+++ b/Source/cmGeneratorTarget.cxx
@@ -8152,6 +8152,20 @@ void cmGeneratorTarget::ComputeLinkImplementationLibraries(
     // Keep this logic in sync with ExpandLinkItems.
     cmGeneratorExpressionDAGChecker dagChecker(this, "LINK_LIBRARIES", nullptr,
                                                nullptr);
+    // The $<LINK_ONLY> expression may be used to specify link dependencies
+    // that are otherwise excluded from usage requirements.
+    if (implFor == LinkInterfaceFor::Usage) {
+      switch (this->GetPolicyStatusCMP0131()) {
+        case cmPolicies::WARN:
+        case cmPolicies::OLD:
+          break;
+        case cmPolicies::REQUIRED_IF_USED:
+        case cmPolicies::REQUIRED_ALWAYS:
+        case cmPolicies::NEW:
+          dagChecker.SetTransitivePropertiesOnly();
+          break;
+      }
+    }
     cmGeneratorExpression ge(entry.Backtrace);
     std::unique_ptr<cmCompiledGeneratorExpression> const cge =
       ge.Parse(entry.Value);