initialize sys.path in jython engine with script's parent directory

second part of the feature requested in #112

Author: Gubaer

src/main/java/org/openstreetmap/josm/plugins/scripting/ui/ScriptExecutor.java

@@ -103,8 +103,15 @@ public void runScriptWithPluggedEngine(
             final var bindings = engine.createBindings();
             // For a python script we initialize the bindings as follows:
             //    __file__ = <full path to script file>
+            //    add the script's parent directory to sys.path
             if (desc.isJython()) {
                 bindings.put("__file__", scriptFile.getPath());
+                final var sysPathStatement = format("import sys; sys.path.append(''{0}'')", scriptFile.getParent());
+                try {
+                    engine.eval(sysPathStatement);
+                } catch(ScriptException e) {
+                    logger.log(Level.WARNING, format("Failed to add ''{0}'' to sys.path", scriptFile.getParent()), e);
+                }
             }
             try {
                 if (engine instanceof Compilable) {

src/test/unit/groovy/org/openstreetmap/josm/plugins/scripting/jsr223/JythonBindingsTest.groovy

@@ -7,13 +7,16 @@ import org.openstreetmap.josm.plugins.scripting.model.ScriptEngineMetaDataProvid
 import org.openstreetmap.josm.plugins.scripting.ui.ScriptExecutor
 
 import static org.junit.Assert.assertEquals
+import static org.junit.Assert.assertTrue
 
 class JythonBindingsTest extends JOSMFixtureBasedTest {
 
     public static String __file__holder = null
+    public static boolean scriptPathInSysPath = false
+    public static int sum = 0
 
     @Test
-    void ensureDefaultBindingsAreSet() {
+    void ensure__file__IsSet() {
         final jythonDesc = ScriptEngineMetaDataProvider
             .getAvailablePluggedScriptEngines()
             .filter(desc -> desc.isJython())
@@ -32,4 +35,60 @@ JythonBindingsTest.__file__holder = __file__
         assertEquals(scriptFile.getPath(), __file__holder)
         scriptFile.delete()
     }
+
+    @Test
+    void ensureSysPathIsSet() {
+        final jythonDesc = ScriptEngineMetaDataProvider
+                .getAvailablePluggedScriptEngines()
+                .filter(desc -> desc.isJython())
+                .findAny()
+                .orElseThrow(() -> new IllegalStateException("No Jython scripting engine found"))
+
+        final executor = new ScriptExecutor(MainApplication.getMainFrame())
+
+        // generate temporary script file
+        final scriptFile = File.createTempFile("test-script", "")
+        scriptFile.write("""
+import sys
+from org.openstreetmap.josm.plugins.scripting.jsr223 import JythonBindingsTest 
+for path in sys.path:
+    if path == '${scriptFile.parent}':
+        JythonBindingsTest.scriptPathInSysPath = True 
+        """)
+        executor.runScriptWithPluggedEngine(jythonDesc, scriptFile)
+        assertTrue(scriptPathInSysPath)
+        scriptFile.delete()
+    }
+
+    @Test
+    void ensureImportFromSysPathWorks() {
+        final jythonDesc = ScriptEngineMetaDataProvider
+                .getAvailablePluggedScriptEngines()
+                .filter(desc -> desc.isJython())
+                .findAny()
+                .orElseThrow(() -> new IllegalStateException("No Jython scripting engine found"))
+
+        final executor = new ScriptExecutor(MainApplication.getMainFrame())
+
+        // generate temporary script file
+        final scriptDir = File.createTempDir()
+        final moduleFile = new File(scriptDir, "my_module.py")
+        final scriptFile = new File(scriptDir, "my_script.py")
+
+
+        moduleFile.write("""
+def add(a, b):
+    return a + b
+        """)
+        scriptFile.write("""
+from org.openstreetmap.josm.plugins.scripting.jsr223 import JythonBindingsTest 
+from my_module import add
+JythonBindingsTest.sum = add(5,3)
+""")
+        executor.runScriptWithPluggedEngine(jythonDesc, scriptFile)
+        assertEquals(8, sum)
+        scriptFile.delete()
+        moduleFile.delete()
+
+    }
 }