Define LINK_DEPENDS target property (#11406)

Custom Makefile link rules may need to depend on linker scripts.  Define
this property to allow user-specified link-time dependencies.

Source/cmMakefileTargetGenerator.cxx

@@ -1534,6 +1534,13 @@ void cmMakefileTargetGenerator
     {
     depends.push_back(*obj);
     }
+
+  // Add user-specified dependencies.
+  if(const char* linkDepends =
+     this->Target->GetProperty("LINK_DEPENDS"))
+    {
+    cmSystemTools::ExpandListArgument(linkDepends, depends);
+    }
 }
 
 //----------------------------------------------------------------------------

Source/cmTarget.cxx

@@ -531,6 +531,18 @@ void cmTarget::DefineProperties(cmake *cm)
      "Use the MAP_IMPORTED_CONFIG_<CONFIG> property to map imported "
      "configurations explicitly.");
 
+  cm->DefineProperty
+    ("LINK_DEPENDS", cmProperty::TARGET,
+     "Additional files on which a target binary depends for linking.",
+     "Specifies a semicolon-separated list of full-paths to files on which "
+     "the link rule for this target depends.  "
+     "The target binary will be linked if any of the named files is newer "
+     "than it."
+     "\n"
+     "This property is ignored by non-Makefile generators.  "
+     "It is intended to specify dependencies on \"linker scripts\" for "
+     "custom Makefile link rules.");
+
   cm->DefineProperty
     ("LINK_INTERFACE_LIBRARIES", cmProperty::TARGET,
      "List public interface libraries for a shared library or executable.",

Tests/BuildDepends/CMakeLists.txt

@@ -34,6 +34,12 @@ if(WIN32 AND "${CMAKE_CXX_COMPILER_ID}" MATCHES "Intel")
   set(_cmake_options "-DCMAKE_EXE_LINKER_FLAGS=")
 endif()
 
+if("${CMAKE_GENERATOR}" MATCHES "Make")
+  set(TEST_LINK_DEPENDS ${BuildDepends_BINARY_DIR}/Project/linkdep.txt)
+  file(WRITE ${TEST_LINK_DEPENDS} "1")
+endif()
+list(APPEND _cmake_options "-DTEST_LINK_DEPENDS=${TEST_LINK_DEPENDS}")
+
 file(MAKE_DIRECTORY ${BuildDepends_BINARY_DIR}/Project)
 message("Creating Project/foo.cxx")
 write_file(${BuildDepends_BINARY_DIR}/Project/foo.cxx 
@@ -131,6 +137,10 @@ file(WRITE ${BuildDepends_BINARY_DIR}/Project/zot_macro_dir.hxx
 file(WRITE ${BuildDepends_BINARY_DIR}/Project/zot_macro_tgt.hxx
   "static const char* zot_macro_tgt = \"zot_macro_tgt changed\";\n")
 
+if(TEST_LINK_DEPENDS)
+  file(WRITE ${TEST_LINK_DEPENDS} "2")
+endif()
+
 help_xcode_depends()
 
 message("Building project second time")
@@ -194,3 +204,16 @@ if("${out}" STREQUAL "${VALUE_CHANGED}")
 else("${out}" STREQUAL "${VALUE_CHANGED}")
   message(SEND_ERROR "Project did not rebuild properly!")
 endif("${out}" STREQUAL "${VALUE_CHANGED}")
+
+if(TEST_LINK_DEPENDS)
+  set(linkdep ${BuildDepends_BINARY_DIR}/Project/linkdep${CMAKE_EXECUTABLE_SUFFIX})
+  if(${linkdep} IS_NEWER_THAN ${TEST_LINK_DEPENDS})
+    message("LINK_DEPENDS worked")
+  else()
+    message(SEND_ERROR "LINK_DEPENDS failed.  Executable
+  ${linkdep}
+is not newer than dependency
+  ${TEST_LINK_DEPENDS}
+")
+  endif()
+endif()

Tests/BuildDepends/Project/CMakeLists.txt

@@ -80,3 +80,8 @@ set_property(
   DIRECTORY
   PROPERTY IMPLICIT_DEPENDS_INCLUDE_TRANSFORM "ZOT_DIR(%)=<zot_%_dir.hxx>"
   )
+
+if(TEST_LINK_DEPENDS)
+  add_executable(linkdep linkdep.cxx)
+  set_property(TARGET linkdep PROPERTY LINK_DEPENDS ${TEST_LINK_DEPENDS})
+endif()

Tests/BuildDepends/Project/linkdep.cxx

@@ -0,0 +1,4 @@
+int main()
+{
+  return 0;
+}