[GR-55528] Fix parsing pyvenv.cfg home property according to PEP 405

Author: timfel

CHANGELOG.md

@@ -12,6 +12,7 @@ language runtime. The main focus is on user-observable behavior of the engine.
 * `polyglot.eval` now raises more meaningful exceptions. Unavaliable languages raise `ValueError`. Exceptions from the polyglot language are raised directly as interop objects (typed as `polyglot.ForeignException`). The shortcut for executing python files without specifying language has been removed, use regular `eval` for executing Python code.
 * In Jython emulation mode we now magically fall back to calling Java getters or setters when using Python attribute access for non-visible properties. This can help migrating away from Jython if you relied on this behavior. 
 * The option `python.EmulateJython` to enable Jython emulation is now marked as stable, and can thus be relied upon in production.
+* Fixed parsing of pyvenv.cfg according to PEP 405, which is required to use [uv](https://github.com/astral-sh/uv?tab=readme-ov-file#uv) generated venvs with GraalPy.
 
 ## Version 24.0.0
 * We now provide a collection of recipes in the form of GitHub Actions to build popular native extensions on GraalPy. These provide a reproducible way for the community to build native extensions for GraalPy with the correct dependencies. See scripts/wheelbuilder/README.md for details.

graalpython/com.oracle.graal.python.shell/src/com/oracle/graal/python/shell/GraalPythonMain.java

@@ -907,7 +907,26 @@ private void findAndApplyVenvCfg(Builder contextBuilder, String executable) {
                 }
                 String name = parts[0].trim();
                 if (name.equals("home")) {
-                    contextBuilder.option("python.PythonHome", parts[1].trim());
+                    Path homeProperty = Paths.get(parts[1].trim());
+                    /*
+                     * (tfel): According to PEP 405, the home key is the directory of the Python
+                     * executable from which this virtual environment was created, that is, it
+                     * usually ends with "/bin" on a Unix system. On Windows, the base Python should
+                     * be in the top-level directory or under "\Scripts". To support running from
+                     * Maven artifacts where we don't have a working executable, we patched our
+                     * shipped venv module to set the home path without a "/bin" or "\\Scripts"
+                     * suffix, so we explicitly check for those two subfolder cases and otherwise
+                     * assume the home key is directly pointing to the Python home.
+                     */
+                    if (homeProperty.endsWith("bin") || homeProperty.endsWith("Scripts")) {
+                        homeProperty = homeProperty.getParent();
+                    }
+                    try {
+                        contextBuilder.option("python.PythonHome", homeProperty.toString());
+                    } catch (NullPointerException ex) {
+                        // NullPointerException covers the possible null result of getParent()
+                        warn("Could not set PYTHONHOME according to the pyvenv.cfg file.");
+                    }
                     String sysPrefix = null;
                     try {
                         sysPrefix = venvCfg.getParent().toAbsolutePath().toString();