GenEx: Add support for custom transitive link properties

Teach the `$<TARGET_PROPERTY:...>` generator expression to check for a
new `TRANSITIVE_LINK_PROPERTIES` property in the target's link
closure to enable transitive evaluation of named properties through
the link closure, including entries guarded by `$<LINK_ONLY:...>`.

Fixes: #20416

3 files changed, 29 insertions, 3 deletions

diff --git a/Help/manual/cmake-buildsystem.7.rst b/Help/manual/cmake-buildsystem.7.rst
index 4dc2306..eb25a4a 100644
--- a/Help/manual/cmake-buildsystem.7.rst
+++ b/Help/manual/cmake-buildsystem.7.rst
@@ -614,7 +614,8 @@ The :genex:`TARGET_PROPERTY` generator expression evaluates the above
 `usage requirement <Target Usage Requirements_>`_ properties
 as builtin transitive properties.  It also supports custom transitive
 properties defined by the :prop_tgt:`TRANSITIVE_COMPILE_PROPERTIES`
-property on the target and its link dependencies.
+and :prop_tgt:`TRANSITIVE_LINK_PROPERTIES` properties on the target
+and its link dependencies.
 
 For example:
 
@@ -623,21 +624,26 @@ For example:
   add_library(example INTERFACE)
   set_target_properties(example PROPERTIES
     TRANSITIVE_COMPILE_PROPERTIES "CUSTOM_C"
+    TRANSITIVE_LINK_PROPERTIES    "CUSTOM_L"
 
     INTERFACE_CUSTOM_C "EXAMPLE_CUSTOM_C"
+    INTERFACE_CUSTOM_L "EXAMPLE_CUSTOM_L"
     )
 
   add_library(mylib STATIC mylib.c)
   target_link_libraries(mylib PRIVATE example)
   set_target_properties(mylib PROPERTIES
     CUSTOM_C           "MYLIB_PRIVATE_CUSTOM_C"
+    CUSTOM_L           "MYLIB_PRIVATE_CUSTOM_L"
     INTERFACE_CUSTOM_C "MYLIB_IFACE_CUSTOM_C"
+    INTERFACE_CUSTOM_L "MYLIB_IFACE_CUSTOM_L"
     )
 
   add_executable(myexe myexe.c)
   target_link_libraries(myexe PRIVATE mylib)
   set_target_properties(myexe PROPERTIES
     CUSTOM_C "MYEXE_CUSTOM_C"
+    CUSTOM_L "MYEXE_CUSTOM_L"
     )
 
   add_custom_target(print ALL VERBATIM
@@ -645,8 +651,14 @@ For example:
       # Prints "MYLIB_PRIVATE_CUSTOM_C;EXAMPLE_CUSTOM_C"
       "$<TARGET_PROPERTY:mylib,CUSTOM_C>"
 
+      # Prints "MYLIB_PRIVATE_CUSTOM_L;EXAMPLE_CUSTOM_L"
+      "$<TARGET_PROPERTY:mylib,CUSTOM_L>"
+
       # Prints "MYEXE_CUSTOM_C"
       "$<TARGET_PROPERTY:myexe,CUSTOM_C>"
+
+      # Prints "MYEXE_CUSTOM_L;MYLIB_IFACE_CUSTOM_L;EXAMPLE_CUSTOM_L"
+      "$<TARGET_PROPERTY:myexe,CUSTOM_L>"
     )
 
 .. _`Compatible Interface Properties`:
diff --git a/Help/manual/cmake-generator-expressions.7.rst b/Help/manual/cmake-generator-expressions.7.rst
index d0d751b..bc32452 100644
--- a/Help/manual/cmake-generator-expressions.7.rst
+++ b/Help/manual/cmake-generator-expressions.7.rst
@@ -1818,7 +1818,7 @@ The expressions have special evaluation rules for some properties:
   * Evaluation of :genex:`$<TARGET_PROPERTY:tgt,PROP>` for some property
     ``PROP``, named without an ``INTERFACE_`` prefix,
     checks the :prop_tgt:`TRANSITIVE_COMPILE_PROPERTIES`
-    property on target ``tgt``,
+    and :prop_tgt:`TRANSITIVE_LINK_PROPERTIES` properties on target ``tgt``,
     on targets named by its :prop_tgt:`LINK_LIBRARIES`, and on the
     transitive closure of targets named by the linked targets'
     :prop_tgt:`INTERFACE_LINK_LIBRARIES`.
@@ -1834,10 +1834,15 @@ The expressions have special evaluation rules for some properties:
       the closure of the linked targets' :prop_tgt:`INTERFACE_LINK_LIBRARIES`,
       excluding entries guarded by the :genex:`LINK_ONLY` generator expression.
 
+    * If ``PROP`` is named by :prop_tgt:`TRANSITIVE_LINK_PROPERTIES`,
+      evaluation of the corresponding ``INTERFACE_PROP`` is transitive over
+      the closure of the linked targets' :prop_tgt:`INTERFACE_LINK_LIBRARIES`,
+      including entries guarded by the :genex:`LINK_ONLY` generator expression.
+
   * Evaluation of :genex:`$<TARGET_PROPERTY:tgt,INTERFACE_PROP>` for some
     property ``INTERFACE_PROP``, named with an ``INTERFACE_`` prefix,
     checks the :prop_tgt:`TRANSITIVE_COMPILE_PROPERTIES`
-    property on target ``tgt``,
+    and :prop_tgt:`TRANSITIVE_LINK_PROPERTIES` properties on target ``tgt``,
     and on the transitive closure of targets named by its
     :prop_tgt:`INTERFACE_LINK_LIBRARIES`.
 
@@ -1853,6 +1858,14 @@ The expressions have special evaluation rules for some properties:
       the closure of the target's :prop_tgt:`INTERFACE_LINK_LIBRARIES`,
       excluding entries guarded by the :genex:`LINK_ONLY` generator expression.
 
+    * If ``PROP`` is named by :prop_tgt:`TRANSITIVE_LINK_PROPERTIES`,
+      evaluation of the corresponding ``INTERFACE_PROP`` is transitive over
+      the closure of the target's :prop_tgt:`INTERFACE_LINK_LIBRARIES`,
+      including entries guarded by the :genex:`LINK_ONLY` generator expression.
+
+  If a ``PROP`` is named by both :prop_tgt:`TRANSITIVE_COMPILE_PROPERTIES`
+  and :prop_tgt:`TRANSITIVE_LINK_PROPERTIES`, the latter takes precedence.
+
 :ref:`Compatible Interface Properties`
   These evaluate as a single value combined from the target itself,
   from targets named by the target's :prop_tgt:`LINK_LIBRARIES`, and
diff --git a/Help/manual/cmake-properties.7.rst b/Help/manual/cmake-properties.7.rst
index 48e1d54..549ec53 100644
--- a/Help/manual/cmake-properties.7.rst
+++ b/Help/manual/cmake-properties.7.rst
@@ -402,6 +402,7 @@ Properties on Targets
    /prop_tgt/SYSTEM
    /prop_tgt/TEST_LAUNCHER
    /prop_tgt/TRANSITIVE_COMPILE_PROPERTIES
+   /prop_tgt/TRANSITIVE_LINK_PROPERTIES
    /prop_tgt/TYPE
    /prop_tgt/UNITY_BUILD
    /prop_tgt/UNITY_BUILD_BATCH_SIZE