Optimize adding test commands in catch_discover_tests

The previous approach was for `add_command` to behave as append function
via concatenating the command string internally and then saving it into
`PARENT_SCOPE`. Because this in practice ended up meaning concatenating
a copy of the string inside the function and then overwriting the string
outside the function, the performance was lacking.

The new approach is for `prepare_command` to only escape & return the
command from single call, and the caller is responsible for concatenating
the result. Since the actual concatenation no longer crosses function
scope boundaries, the performance is much better, even though the scaling
is still quadratic.

The new approach only takes 1/4-1/5 of the time, saving ~1s at 1k tests,
4.5s at 2k tests and 19s at 4k tests.

1 files changed, 61 insertions, 0 deletions

diff --git a/tests/TestScripts/DiscoverTests/TestPrepareCommand.cmake b/tests/TestScripts/DiscoverTests/TestPrepareCommand.cmake
new file mode 100644
index 00000000..f02bb409
--- /dev/null
+++ b/tests/TestScripts/DiscoverTests/TestPrepareCommand.cmake
@@ -0,0 +1,61 @@
+# SPDX-License-Identifier: BSL-1.0
+
+# Unit tests for `prepare_command` helper in `extras/CatchAddTests.cmake`.
+#
+# Yes, we are at the stage where the script helpers need unit tests.
+#
+# Run as
+#     cmake -DCATCH_ADD_TESTS_SCRIPT=/path/to/extras/CatchAddTests.cmake \
+#           -P TestPrepareCommand.cmake
+
+
+cmake_minimum_required(VERSION 3.19)
+
+if(NOT DEFINED CATCH_ADD_TESTS_SCRIPT)
+  message(FATAL_ERROR "Missing argument `CATCH_ADD_TESTS_SCRIPT`")
+endif()
+
+if(NOT EXISTS "${CATCH_ADD_TESTS_SCRIPT}")
+  message(FATAL_ERROR "Cannot find CatchAddTests.cmake at '${CATCH_ADD_TESTS_SCRIPT}'")
+endif()
+
+# Pull in the helper functions. Without `TEST_EXECUTABLE` being defined,
+# `catch_discover_tests_impl` is not called.
+include("${CATCH_ADD_TESTS_SCRIPT}")
+
+set(_failures 0)
+
+function(expect_equal description actual expected)
+  if(actual STREQUAL expected)
+    message("  [PASS] ${description}")
+  else()
+    message("  [FAIL] ${description}")
+    message("         expected: [${expected}]")
+    message("         actual:   [${actual}]")
+    math(EXPR _n "${_failures} + 1")
+    set(_failures "${_n}" PARENT_SCOPE)
+  endif()
+endfunction()
+
+prepare_command(add_test SimpleName /path/to/tests)
+expect_equal("Simple arg, no quotes" "${_Command}" "add_test( SimpleName /path/to/tests)\n")
+
+prepare_command(add_test "Name with spaces")
+expect_equal("Spaces in arg, needs quotes" "${_Command}" "add_test( [==[Name with spaces]==])\n")
+
+prepare_command(set_tests_properties Foo PROPERTIES LABELS "tagA\;tagB\;tagC")
+expect_equal("semicolons in argument are kept and quoted"
+  "${_Command}" "set_tests_properties( Foo PROPERTIES LABELS [==[tagA\;tagB\;tagC]==])\n")
+
+set(_Command "PRE-EXISTING")
+prepare_command(set_tests_properties Foo PROPERTIES BAR baz)
+expect_equal("_Command var does no accumulate commands"
+  "${_Command}" "set_tests_properties( Foo PROPERTIES BAR baz)\n")
+
+
+
+if(_failures GREATER 0)
+  message(FATAL_ERROR "${_failures} prepare_command test(s) failed")
+else()
+  message(STATUS "All prepare_command tests passed")
+endif()