GenEx $<PATH>: Add NATIVE_PATH sub-command.

Implements the generator expression $<PATH:MATIVE_PATH> which convert
path(s) into a native format with platform-specific slashes (``\`` on
Windows hosts and ``/`` elsewhere).

Fixes: #26515

Help/manual/cmake-generator-expressions.7.rst

@@ -795,6 +795,16 @@ in cmake-style format.
   When the ``NORMALIZE`` option is specified, the path is :ref:`normalized
   <Normalization>` after the conversion.
 
+.. genex:: $<PATH:NATIVE_PATH[,NORMALIZE],path...>
+
+  .. versionadded:: 3.32
+
+  Returns ``path`` converted into a native format with platform-specific
+  slashes (``\`` on Windows hosts and ``/`` elsewhere).
+
+  When the ``NORMALIZE`` option is specified, the path is :ref:`normalized
+  <Normalization>` before the conversion.
+
 .. genex:: $<PATH:APPEND,path...,input,...>
 
   .. versionadded:: 3.24

Help/release/dev/GenEx-PATH-NATIVE_PATH.rst

@@ -0,0 +1,5 @@
+GenEx-PATH-NATIVE_PATH
+----------------------
+
+* The :genex:`$<PATH>` generator expression gains the sub-command
+  ``NATIVE_PATH`` to convert a CMake path into a native one.

Source/cmGeneratorExpressionNode.cxx

@@ -982,6 +982,27 @@ static const struct PathNode : public cmGeneratorExpressionNode
             }
             return std::string{};
           } },
+        { "NATIVE_PATH"_s,
+          [](cmGeneratorExpressionContext* ctx,
+             const GeneratorExpressionContent* cnt,
+             Arguments& args) -> std::string {
+            bool normalize = args.front() == "NORMALIZE"_s;
+            if (normalize) {
+              args.advance(1);
+            }
+            if (CheckPathParametersEx(ctx, cnt,
+                                      normalize ? "NATIVE_PATH,NORMALIZE"_s
+                                                : "NATIVE_PATH"_s,
+                                      args.size(), 1)) {
+              return processList(
+                args.front(), [normalize](std::string& value) {
+                  auto path = cmCMakePath{ value };
+                  value = normalize ? path.Normal().NativeString()
+                                    : path.NativeString();
+                });
+            }
+            return std::string{};
+          } },
         { "APPEND"_s,
           [](cmGeneratorExpressionContext* ctx,
              const GeneratorExpressionContent* cnt,

Tests/RunCMake/GenEx-PATH/NATIVE_PATH.cmake.in

@@ -0,0 +1,48 @@
+
+include ("${RunCMake_SOURCE_DIR}/check_errors.cmake")
+unset (errors)
+
+cmake_path(SET test_path "/x/y/z/../../a/d")
+cmake_path(NATIVE_PATH test_path reference)
+set(output [=[$<PATH:NATIVE_PATH,/x/y/z/../../a/d>]=])
+if (NOT output STREQUAL reference)
+  list (APPEND errors "'${output}' instead of '${reference}'")
+endif()
+cmake_path(SET test_path "/x/y/z/../../a/d")
+cmake_path(NATIVE_PATH test_path NORMALIZE reference)
+set(output [=[$<PATH:NATIVE_PATH,NORMALIZE,/x/y/z/../../a/d>]=])
+if (NOT output STREQUAL reference)
+  list (APPEND errors "'${output}' instead of '${reference}'")
+endif()
+
+
+######################################
+## tests with list of paths
+######################################
+unset(reference)
+foreach(path IN ITEMS "/x/y/z/../../a/d" "/x/y/z/../../b/e")
+  cmake_path(SET test_path "${path}")
+  cmake_path(NATIVE_PATH test_path result)
+  list(APPEND reference "${result}")
+endforeach()
+
+set(output [=[$<PATH:NATIVE_PATH,/x/y/z/../../a/d;/x/y/z/../../b/e>]=])
+if (NOT output STREQUAL reference)
+  list (APPEND errors "'${output}' instead of '${reference}'")
+endif()
+
+unset(reference)
+foreach(path IN ITEMS "/x/y/z/../../a/d" "/x/y/z/../../b/e")
+  cmake_path(SET test_path "${path}")
+  cmake_path(NATIVE_PATH test_path NORMALIZE result)
+  list(APPEND reference "${result}")
+endforeach()
+set(output [=[$<PATH:NATIVE_PATH,NORMALIZE,/x/y/z/../../a/d;/x/y/z/../../b/e>]=])
+if (NOT output STREQUAL reference)
+  list (APPEND errors "'${output}' instead of '${reference}'")
+endif()
+
+
+
+
+check_errors("PATH:NATIVE_PATH" ${errors})

Tests/RunCMake/GenEx-PATH/RunCMakeTest.cmake

@@ -16,7 +16,7 @@ foreach (subcommand IN ITEMS GET_ROOT_NAME GET_ROOT_DIRECTORY GET_ROOT_PATH GET_
                              GET_EXTENSION GET_STEM GET_RELATIVE_PART GET_PARENT_PATH
                              HAS_ROOT_NAME HAS_ROOT_DIRECTORY HAS_ROOT_PATH HAS_FILENAME
                              HAS_EXTENSION HAS_STEM HAS_RELATIVE_PART HAS_PARENT_PATH
-                             IS_ABSOLUTE IS_RELATIVE CMAKE_PATH REMOVE_FILENAME REMOVE_EXTENSION
+                             IS_ABSOLUTE IS_RELATIVE CMAKE_PATH NATIVE_PATH REMOVE_FILENAME REMOVE_EXTENSION
                              NORMAL_PATH)
   check_path_syntax (${subcommand} unexpected-arg "-DPATH_ARGUMENTS=${subcommand},ARG1,ARG2")
 endforeach()
@@ -27,7 +27,7 @@ foreach (subcommand IN ITEMS GET_EXTENSION GET_STEM REMOVE_EXTENSION)
   check_path_syntax ("${subcommand}[LAST_ONLY]" unexpected-arg "-DPATH_ARGUMENTS=${subcommand},LAST_ONLY,ARG1,ARG2")
   unset(RunCMake-stderr-file)
 endforeach()
-foreach (subcommand IN ITEMS CMAKE_PATH)
+foreach (subcommand IN ITEMS CMAKE_PATH NATIVE_PATH)
   check_path_syntax ("${subcommand}[NORMALIZE]" unexpected-arg "-DPATH_ARGUMENTS=${subcommand},NORMALIZE,ARG1,ARG2")
 endforeach()
 
@@ -57,6 +57,7 @@ endfunction()
 check_path_execution (GET_ITEM)
 check_path_execution (HAS_ITEM)
 check_path_execution (CMAKE_PATH)
+check_path_execution (NATIVE_PATH)
 check_path_execution (APPEND)
 check_path_execution (REMOVE_ITEM)
 check_path_execution (REPLACE_ITEM)