Epic bug: pyexpat fiddles incorrectly with the systrace function. This is a hack to make it behave correctly with coverage.py. Fixes bug #10.

3 files changed, 68 insertions, 1 deletions

diff --git a/CHANGES.txt b/CHANGES.txt
index 488ab3d..9f4ec39 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -12,6 +12,9 @@ Version 3.next
   mode just like Python does.  This lets it run Windows files on Mac, for

   example.

 

+- Fixed a bizarre problem involving pyexpat, whereby lines following XML parser

+  invocations could be overlooked.

+

 

 Version 3.0, 13 June 2009

 -------------------------

diff --git a/coverage/tracer.c b/coverage/tracer.c
index 50a25be..15a17b2 100644
--- a/coverage/tracer.c
+++ b/coverage/tracer.c
@@ -198,6 +198,25 @@ Tracer_trace(Tracer *self, PyFrameObject *frame, int what, PyObject *arg)
         break;

     }

 

+    /* UGLY HACK: for some reason, pyexpat invokes the systrace function directly.

+       It uses "pyexpat.c" as the filename, which is strange enough, but it calls

+       it incorrectly: when an exception passes through the C code, it calls trace

+       with an EXCEPTION, but never calls RETURN.  This throws off our bookkeeping.

+       To make things right, if this is an EXCEPTION from pyexpat.c, then inject

+       a RETURN event also.  If the bug in pyexpat.c gets fixed someday, we'll 

+       either have to put a version check here, or do something more sophisticated

+       to detect the EXCEPTION-without-RETURN case that has to be fixed up.

+    */

+    if (what == PyTrace_EXCEPTION) {

+        if (strstr(PyString_AS_STRING(frame->f_code->co_filename), "pyexpat.c")) {

+            /* Stupid pyexpat: pretend it gave us the RETURN it should have. */

+            SHOWLOG(self->depth, frame->f_lineno, frame->f_code->co_filename, "wrongexc");

+            if (Tracer_trace(self, frame, PyTrace_RETURN, arg) < 0) {

+                return -1;

+            }

+        }

+    }

+

     return 0;

 }

 

diff --git a/test/test_coverage.py b/test/test_coverage.py
index 30ac4b8..2d08281 100644
--- a/test/test_coverage.py
+++ b/test/test_coverage.py
@@ -1704,6 +1704,51 @@ class RecursionTest(CoverageTest):
             [1,2,3,5,7], "")
 
 
+class PyexpatTest(CoverageTest):
+    """Pyexpat screws up tracing. Make sure we've counter-defended properly."""
+    def testPyexpat(self):
+        # pyexpat calls the trace function explicitly (inexplicably), and does
+        # it wrong for exceptions.  Parsing a DOCTYPE for some reason throws
+        # an exception internally, and triggers its wrong behavior.  This test
+        # checks that our fake PyTrace_RETURN hack in tracer.c works.  It will
+        # also detect if the pyexpat bug is fixed unbeknownst to us, meaning
+        # we'd see two RETURNs where there should only be one.
+
+        self.makeFile("trydom.py", """\
+            import xml.dom.minidom
+
+            XML = '''\\
+            <!DOCTYPE fooey SYSTEM "http://www.example.com/example.dtd">
+            <root><child/><child/></root>
+            '''
+
+            def foo():
+                dom = xml.dom.minidom.parseString(XML)
+                assert len(dom.getElementsByTagName('child')) == 2
+                print "Parsed"
+
+            foo()
+            """)
+
+        self.makeFile("outer.py", "\n"*100 + "import trydom\nprint 'done'\n")
+
+        cov = coverage.coverage()
+        cov.erase()
+
+        # Import the python file, executing it.
+        cov.start()
+        self.importModule("outer")
+        cov.stop()
+
+        _, statements, missing, _ = cov.analysis("trydom.py")
+        self.assertEqual(statements, [1,3,8,9,10,11,13])
+        self.assertEqual(missing, [])
+    
+        _, statements, missing, _ = cov.analysis("outer.py")
+        self.assertEqual(statements, [101,102])
+        self.assertEqual(missing, [])
+
+
 if __name__ == '__main__':
     print "Testing under Python version: %s" % sys.version
     unittest.main()
@@ -1714,4 +1759,4 @@ if __name__ == '__main__':
 #         in an expression!)
 # TODO: Generator comprehensions? 
 # TODO: Constant if tests ("if 1:").  Py 2.4 doesn't execute them.
-# TODO: There are no tests for analysis2 directly.
\ No newline at end of file
+# TODO: There are no tests for analysis2 directly.