Implement writing the __cause__ attribute on exceptions. (pythonnet#287)

filmor · denfromufa · commit 071f25dc9ec4 · 2016-11-21T11:45:46.000-06:00
diff --git a/src/runtime/clrobject.cs b/src/runtime/clrobject.cs
@@ -31,8 +31,9 @@ internal CLRObject(Object ob, IntPtr tp) : base()
             this.gcHandle = gc;
             inst = ob;
 
-            // Fix the BaseException args slot if wrapping a CLR exception
-            Exceptions.SetArgs(py);
+            // Fix the BaseException args (and __cause__ in case of Python 3)
+            // slot if wrapping a CLR exception
+            Exceptions.SetArgsAndCause(py);
         }
 
 
@@ -70,4 +71,4 @@ internal static IntPtr GetInstHandle(Object ob)
             return co.pyHandle;
         }
     }
-}
+}
diff --git a/src/runtime/exceptions.cs b/src/runtime/exceptions.cs
@@ -144,7 +144,7 @@ internal static void Shutdown()
         /// </summary>
         /// <param name="e">A CLR exception</param>
         /// <param name="ob">The python object wrapping </param>
-        internal static void SetArgs(IntPtr ob)
+        internal static void SetArgsAndCause(IntPtr ob)
         {
             var e = ExceptionClassObject.ToException(ob);
             if (e == null)
@@ -163,6 +163,14 @@ internal static void SetArgs(IntPtr ob)
             }
 
             Marshal.WriteIntPtr(ob, ExceptionOffset.args, args);
+
+#if !(PYTHON25 || PYTHON26 || PYTHON27)
+            if (e.InnerException != null)
+            {
+                IntPtr cause = CLRObject.GetInstHandle(e.InnerException);
+                Marshal.WriteIntPtr(ob, ExceptionOffset.cause, cause);
+            }
+#endif
         }
 
         /// <summary>
@@ -434,4 +442,4 @@ puplic static variables on the Exceptions class filled in from
         //PyAPI_DATA(PyObject *) PyExc_BytesWarning;
 #endif
     }
-}
+}
diff --git a/src/testing/exceptiontest.cs b/src/testing/exceptiontest.cs
@@ -1,6 +1,5 @@
 using System;
 
-
 namespace Python.Test
 {
     //========================================================================
@@ -55,6 +54,25 @@ public static bool ThrowException()
         {
             throw new OverflowException("error");
         }
+
+        public static void ThrowChainedExceptions()
+        {
+            try
+            {
+                try
+                {
+                    throw new Exception("Innermost exception");
+                }
+                catch (Exception exc)
+                {
+                    throw new Exception("Inner exception", exc);
+                }
+            }
+            catch (Exception exc2)
+            {
+                throw new Exception("Outer exception", exc2);
+            }
+        }
     }
 
 
diff --git a/src/tests/test_exceptions.py b/src/tests/test_exceptions.py
@@ -345,6 +345,27 @@ def testPicklingExceptions(self):
 
         self.assertEqual(exc.args, loaded.args)
 
+    def testChainedExceptions(self):
+        if six.PY3:
+            from Python.Test import ExceptionTest
+
+            try:
+                ExceptionTest.ThrowChainedExceptions()
+            except Exception as exc:
+                msgs = [
+                    "Outer exception",
+                    "Inner exception",
+                    "Innermost exception"
+                ]
+
+                for msg in msgs:
+                    self.assertEqual(exc.Message, msg)
+                    self.assertEqual(exc.__cause__, exc.InnerException)
+                    exc = exc.__cause__
+
+            else:
+                self.fail("Test should raise an exception")
+
 
 def test_suite():
     return unittest.makeSuite(ExceptionTests)

Original file line number	Diff line number	Diff line change
`@@ -31,8 +31,9 @@ internal CLRObject(Object ob, IntPtr tp) : base()`
`31`	`31`	`this.gcHandle = gc;`
`32`	`32`	`inst = ob;`
`33`	`33`
`34`		`- // Fix the BaseException args slot if wrapping a CLR exception`
`35`		`- Exceptions.SetArgs(py);`
	`34`	`+ // Fix the BaseException args (and __cause__ in case of Python 3)`
	`35`	`+ // slot if wrapping a CLR exception`
	`36`	`+ Exceptions.SetArgsAndCause(py);`
`36`	`37`	`}`
`37`	`38`
`38`	`39`
`@@ -70,4 +71,4 @@ internal static IntPtr GetInstHandle(Object ob)`
`70`	`71`	`return co.pyHandle;`
`71`	`72`	`}`
`72`	`73`	`}`
`73`		`-}`
	`74`	`+}`