From 218e72763b04cc8976b1e2669e86e2200bc0d74a Mon Sep 17 00:00:00 2001
From: DLuminary <86183013+DLuminary@users.noreply.github.com>
Date: Mon, 24 Aug 2026 13:34:42 +0300
Subject: [PATCH] Escape the path separator when prepending to PYTHONPATH

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.
---
 cmake/MatlabWrap.cmake | 4 +++-
 cmake/PybindWrap.cmake | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/cmake/MatlabWrap.cmake b/cmake/MatlabWrap.cmake
index 55b7cdb..f565e8e 100644
--- a/cmake/MatlabWrap.cmake
+++ b/cmake/MatlabWrap.cmake
@@ -229,7 +229,9 @@ function(wrap_library_internal interfaceHeader moduleName linkLibraries extraInc
   if(UNIX)
     set(GTWRAP_PATH_SEPARATOR ":")
   else()
-    set(GTWRAP_PATH_SEPARATOR ";")
+    # Escaped: an unescaped ";" is CMake's list separator, so it would split
+    # the quoted PYTHONPATH argument below instead of joining two path entries.
+    set(GTWRAP_PATH_SEPARATOR "\\;")
   endif()
 
   # Set boost serialization flag for the python script call below.
diff --git a/cmake/PybindWrap.cmake b/cmake/PybindWrap.cmake
index 2c98b69..9721c8d 100644
--- a/cmake/PybindWrap.cmake
+++ b/cmake/PybindWrap.cmake
@@ -60,7 +60,9 @@ function(
   if(UNIX)
     set(GTWRAP_PATH_SEPARATOR ":")
   else()
-    set(GTWRAP_PATH_SEPARATOR ";")
+    # Escaped: an unescaped ";" is CMake's list separator, so it would split
+    # the quoted PYTHONPATH argument below instead of joining two path entries.
+    set(GTWRAP_PATH_SEPARATOR "\\;")
   endif()
 
   # Create a copy of interface_headers so we can freely manipulate it