X workaround lack of exception chaining on Python2 with xdefer

wcfs/wcfs_test.py

@@ -33,7 +33,7 @@ from persistent import Persistent
 from persistent.timestamp import TimeStamp
 from ZODB.utils import z64
 
-import os, os.path, subprocess, threading
+import sys, os, os.path, subprocess, threading, inspect, traceback
 from errno import EINVAL
 from golang import chan, func, defer, select
 from golang import context, sync, time
@@ -76,6 +76,36 @@ def teardown_function(f):
         os.rmdir(testmntpt)
 
 
+# xdefer is like defer, but makes sure exception raised before deferred
+# function is called is not lost.
+#
+# if deferred function raises exception itself - it prints previous exception to stderr.
+#
+# XXX xdefer is workaround for Python2 not having exception chanining (PEP 3134)
+# without which, if e.g. tDB.close() raises exception, it prevents to see
+# whether and which an assert in the test failed.
+#
+# XXX merge into defer?
+def xdefer(f):
+    # hack - imitate as if defer called from under xdefer was called directly by caller func
+    fgo = inspect.currentframe().f_back.f_back
+    __goframe__ = fgo.f_locals['__goframe__']
+    _xdefer(f)
+
+def _xdefer(f):
+    def _():
+        # call f, but print previous exception if f raises
+        exc_type, exc_value, exc_traceback = sys.exc_info()
+        try:
+            f()
+        except:
+            traceback.print_exception(exc_type, exc_value, exc_traceback)
+            raise
+    defer(_)
+
+
+
+
 # ---- test join/autostart ----
 
 # test that zurl does not change from one open to another storage open.
@@ -94,14 +124,14 @@ def test_join():
         wcfs.join(zurl, autostart=False)
 
     wc = wcfs._start(zurl)
-    defer(wc.close)
+    xdefer(wc.close)
     assert wc.mountpoint == testmntpt
     assert readfile(wc.mountpoint + "/.wcfs/zurl") == zurl
     assert os.path.isdir(wc.mountpoint + "/head")
     assert os.path.isdir(wc.mountpoint + "/head/bigfile")
 
     wc2 = wcfs.join(zurl, autostart=False)
-    defer(wc2.close)
+    xdefer(wc2.close)
     assert wc2.mountpoint == wc.mountpoint
 
 # test that join(autostart=y) works.
@@ -112,7 +142,7 @@ def test_join_autostart():
         wcfs.join(zurl, autostart=False)
 
     wc = wcfs.join(zurl, autostart=True)
-    defer(wc.close)
+    xdefer(wc.close)
     assert wc.mountpoint == testmntpt
     assert readfile(wc.mountpoint + "/.wcfs/zurl") == zurl
     assert os.path.isdir(wc.mountpoint + "/head")
@@ -764,12 +794,11 @@ def _expectPin(w, ctx, zf, expect):
     return reqv
 
 
-
 # test_wcfs exercises wcfs functionality.
 @func
 def test_wcfs():
     t = tDB()
-    defer(t.close)
+    xdefer(t.close)
 
     t.root['!file'] = nonfile = Persistent()
     t.root['zfile'] = zf = ZBigFile(blksize)
@@ -850,11 +879,7 @@ def test_wcfs():
     # XXX -> separate test?
     w = t.openwatch()
     print('\n\nzzzzzzz\n\n')
-    try:
     assert w.sendReq(context.background(), b'bla bla') == ""
-    except:
-        #import traceback; traceback.print_exc()
-        raise
 
     # assert w closed
     print('\n\n0000000\n\n')
@@ -919,21 +944,17 @@ def test_wcfs():
 @func
 def test_wcfs_invproto():
     # XXX temp debug
+    import sys, traceback
 
-    """
     def _():
         print('BBB')
         1/0
-    defer(_)
-    """
+    xdefer(_)
 
     #raise RuntimeError('zzz')
 
-    try:
     print('\nAAA')
     assert 1 == 2
-    finally:
-        2/0
 
 
 # ---- misc ---
@@ -957,7 +978,7 @@ def tidtime(tid):
 @func
 def test_tidtime_notrough():
     t = tDB()
-    defer(t.close)
+    xdefer(t.close)
 
     atprev = t.commit()
     for i in range(10):