ctest fails on Windows: CTestCustom.cmake has unescaped backslashes in CTEST_CUSTOM_PRE_TEST path

[djkees]

Summary

Running ctest in a pFUnit build directory on Windows fails immediately with a CMake parse error, before any tests run, because the generated CTestCustom.cmake embeds a native Windows path (with backslashes) inside a double-quoted CMake string without escaping the backslashes themselves.

Reproduction

• Windows 11, gfortran (conda-forge), CMake 4.4.2, Ninja
• Standard standalone build:

cmake -S . -B build -G Ninja
cmake --build build
cd build
ctest

Fails with:

CMake Error at C:/.../pFUnit/build/CTestCustom.cmake:1 (set):
  Syntax error in cmake code at

    C:/.../pFUnit/build/CTestCustom.cmake:1

  when parsing string

    C:\Users\<user>\...\cmake.exe --build . --config \"Release\" --target \"build-tests\"

  Invalid character escape '\U'.

Problem reading custom configuration: C:/.../pFUnit/build/CTestCustom.cmake

Root cause

Top-level CMakeLists.txt (around line 172-177) generates CTestCustom.cmake like this:

build_command(CTEST_CUSTOM_PRE_TEST TARGET build-tests)
string(CONFIGURE \"@CTEST_CUSTOM_PRE_TEST@\" CTEST_CUSTOM_PRE_TEST_QUOTED ESCAPE_QUOTES)
file(WRITE "${CMAKE_BINARY_DIR}/CTestCustom.cmake" "set(CTEST_CUSTOM_PRE_TEST ${CTEST_CUSTOM_PRE_TEST_QUOTED})" "\n")

build_command() returns the path to the CMake executable using native (backslash) path separators on Windows. string(CONFIGURE ... ESCAPE_QUOTES) only escapes embedded double quotes (" -> \"); it does not escape the backslashes in the path itself. The resulting CTestCustom.cmake therefore contains a raw Windows path with literal backslashes inside a double-quoted string.

When CTest later parses that file as CMake script, backslashes inside a quoted string are interpreted as escape sequences per CMake's own string-escaping rules. \U (from ...\Users\...) is treated as the start of a Unicode escape, which is invalid without following hex digits, so parsing fails and ctest aborts before running any tests - a full functional regression on Windows, not just a cosmetic warning.

Suggested fix

Escape backslashes (in addition to quotes) when embedding the native CTEST_CUSTOM_PRE_TEST command path into the generated CMake string, e.g. by replacing \ with \ before/via string(CONFIGURE ...), or by writing the path with forward slashes instead of relying on build_command()'s native-separator output.

Workaround

Skip CTestCustom.cmake and run the built test executables directly instead of via ctest, e.g. tests/funit-core/funit_tests.x.exe, new_tests.x.exe, filter_cmdline_tests.x.exe, and tests/fhamcrest/fhamcrest_tests.x.exe. All pass cleanly once the build itself succeeds.

Related

Found while verifying the fix in #566 / the accompanying PR.

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Drafted with Claude's assistance.

• Root cause traced by reading the generated build/CTestCustom.cmake output and the file(WRITE ...) call in the top-level CMakeLists.txt that produces it.
• Reproduced consistently on a clean build directory; confirmed the workaround (running the test executables directly) succeeds with all tests passing.

🤖 Generated with Claude Code