Escape the path separator when prepending to PYTHONPATH

[DLuminary]

PybindWrap.cmake and MatlabWrap.cmake build the environment for the wrapper generator as

"PYTHONPATH=${GTWRAP_PACKAGE_DIR}${GTWRAP_PATH_SEPARATOR}$ENV{PYTHONPATH}"

with GTWRAP_PATH_SEPARATOR set to ":" on UNIX and ";" elsewhere. The UNIX branch is fine. On the other branch an unescaped ";" is CMake's list separator, so the quoted argument is split rather than being passed through as a single PYTHONPATH assignment.

When PYTHONPATH is unset the string ends in a trailing ";", the empty second element is dropped, and the command still receives one valid assignment -- which is why this has not been noticed. When PYTHONPATH is set, the split lands in the middle of the command line and the build fails outright.

Reproduced with a minimal project using add_custom_command, forcing the non-UNIX branch:

unescaped ";", PYTHONPATH unset -> ran ok
unescaped ";", PYTHONPATH set   -> Error 127, build fails

escaped   "\;", PYTHONPATH set   -> ran ok, PYTHONPATH=/pkg/dir:/existing
escaped   "\;", PYTHONPATH unset -> ran ok
escaped   "\;", UNIX branch      -> ran ok  (unchanged)

So on Windows the wrapper currently builds only because PYTHONPATH is typically unset; a conda environment or any other setup that defines it would fail before the generator runs.

Note this is not tested on a real Windows host -- the non-UNIX branch was forced on Linux to exercise the same CMake parsing. The UNIX path is unaffected either way.

The same class of bug exists in gtsam's python/CMakeLists.txt, where the four PYTHONPATH-setting targets join with "/" instead of a path-list separator at all; that is fixed separately in borglab/gtsam#2739.

[ProfFan]

Did you test under Windows? I tested with current CMake on Windows and this does not reproduce.

[DLuminary]

You're right — I didn't, and my test was invalid. Sorry.

I forced the non-UNIX branch on Linux, which puts a ; into a Makefile recipe executed by /bin/sh. That's where the split happened, not in CMake. Reading the emitted recipe confirms it: CMake passes the whole string through as one argument, and the shell splits it at the ;.

On Windows the recipe runs under cmd.exe, where ; isn't a command separator — so the branch is safe exactly where it actually runs, which is why you couldn't reproduce it.

I also fixed it in borglab/gtsam#2739.

Closing.