tests: Preserve empty arguments in test command lines

This will now preserve empty values in the TEST_LAUNCHER and
CROSSCOMPILING_EMULATOR target properties for tests added by:

- The add_test() command.
- The ExternalData_Add_Test() command from the ExternalData module.
- The gtest_add_tests() or gtest_discover_tests() commands from the
  GoogleTest module.

For the gtest_add_tests() and gtest_discover_tests() commands,
empty elements in the values passed after the EXTRA_ARGS keyword
are also now preserved.

Policy CMP0178 is added to provide backward compatibility with the
old behavior where empty values were silently discarded from the
above cases.

Fixes: #26337

3 files changed, 57 insertions, 0 deletions

diff --git a/Help/manual/cmake-policies.7.rst b/Help/manual/cmake-policies.7.rst
index 3b97848..796ce8b 100644
--- a/Help/manual/cmake-policies.7.rst
+++ b/Help/manual/cmake-policies.7.rst
@@ -57,6 +57,7 @@ Policies Introduced by CMake 3.31
 .. toctree::
    :maxdepth: 1
 
+   CMP0178: Test command lines preserve empty arguments. </policy/CMP0178>
    CMP0177: install() DESTINATION paths are normalized. </policy/CMP0177>
    CMP0176: execute_process() ENCODING is UTF-8 by default. </policy/CMP0176>
    CMP0175: add_custom_command() rejects invalid arguments. </policy/CMP0175>
diff --git a/Help/policy/CMP0178.rst b/Help/policy/CMP0178.rst
new file mode 100644
index 0000000..f6152eb
--- /dev/null
+++ b/Help/policy/CMP0178.rst
@@ -0,0 +1,37 @@
+CMP0178
+-------
+
+.. versionadded:: 3.31
+
+Test command lines preserve empty arguments.
+
+Empty values in the :prop_tgt:`TEST_LAUNCHER` and
+:prop_tgt:`CROSSCOMPILING_EMULATOR` target properties are now preserved
+for tests added by the following:
+
+* The :command:`add_test` command.
+* The :command:`ExternalData_Add_Test` command from the :module:`ExternalData`
+  module.
+* The :command:`gtest_add_tests` or :command:`gtest_discover_tests` commands
+  from the :module:`GoogleTest` module.
+
+For the :command:`gtest_add_tests` and :command:`gtest_discover_tests`
+commands, empty elements in the values passed after the ``EXTRA_ARGS``
+keyword are also now preserved.
+
+The ``OLD`` behavior of this policy silently discards empty list items
+from the :prop_tgt:`TEST_LAUNCHER` and :prop_tgt:`CROSSCOMPILING_EMULATOR`
+target properties in the above-mentioned cases.  It also silently discards
+empty items from the values given after ``EXTRA_ARGS`` for the
+:command:`gtest_add_tests` and :command:`gtest_discover_tests` commands.
+
+The ``NEW`` behavior of this policy preserves empty list items in the
+:prop_tgt:`TEST_LAUNCHER` and :prop_tgt:`CROSSCOMPILING_EMULATOR` target
+properties, and in values given after ``EXTRA_ARGS`` for
+:command:`gtest_add_tests` and :command:`gtest_discover_tests`.
+
+.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 3.31
+.. |WARNS_OR_DOES_NOT_WARN| replace:: warns
+.. include:: STANDARD_ADVICE.txt
+
+.. include:: DEPRECATED.txt
diff --git a/Help/release/dev/preserve-empty-args-test-command-lines.rst b/Help/release/dev/preserve-empty-args-test-command-lines.rst
new file mode 100644
index 0000000..a533ac8
--- /dev/null
+++ b/Help/release/dev/preserve-empty-args-test-command-lines.rst
@@ -0,0 +1,19 @@
+preserve-empty-args-test-command-lines
+--------------------------------------
+
+* Empty list elements in the :prop_tgt:`TEST_LAUNCHER` and
+  :prop_tgt:`CROSSCOMPILING_EMULATOR` target properties are now preserved
+  when the executable for a command given to :command:`add_test` is a CMake
+  target. See policy :policy:`CMP0178`.
+
+* Empty list elements in the :prop_tgt:`TEST_LAUNCHER` and
+  :prop_tgt:`CROSSCOMPILING_EMULATOR` target properties are now preserved
+  for the test created by :command:`ExternalData_Add_Test` from the
+  :module:`ExternalData` module.  See policy :policy:`CMP0178`.
+
+* Empty list elements in the :prop_tgt:`TEST_LAUNCHER` and
+  :prop_tgt:`CROSSCOMPILING_EMULATOR` target properties are now preserved
+  for tests created by :command:`gtest_add_tests` and
+  :command:`gtest_discover_tests` from the :module:`GoogleTest` module.
+  Empty list elements after the ``EXTRA_ARGS`` keyword of these two commands
+  are also now preserved.  See policy :policy:`CMP0178`.