changeset 20155:21dafd8546d1

parsers: fail fast if Python has wrong minor version (issue4110) This change causes an informative ImportError to be raised when importing the extension module parsers if the minor version of the currently-running Python interpreter doesn't match that of the Python that was used when compiling the extension module. Here is an example of what the new error looks like: Traceback (most recent call last): File "test.py", line 1, in <module> import mercurial.parsers ImportError: Python minor version mismatch: The Mercurial extension modules were compiled with Python 2.7.6, but Mercurial is currently using Python with sys.hexversion=33883888: Python 2.5.6 (r256:88840, Nov 18 2012, 05:37:10) [GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))] at: /opt/local/Library/Frameworks/Python.framework/Versions/2.5/Resources/ Python.app/Contents/MacOS/Python The reason for raising an error in this scenario is that Python's C API is known not to be compatible from minor version to minor version, even if sys.api_version is the same. See for example this Python bug report about incompatibilities between 2.5 and 2.6+: http://bugs.python.org/issue8118 These incompatibilities can cause Mercurial to break in mysterious, unforeseen ways. For example, when Mercurial compiled with Python 2.7 was run with 2.5, the following crash occurred when running "hg status": http://bz.selenic.com/show_bug.cgi?id=4110 After this crash was fixed, running with Python 2.5 no longer crashes, but the following puzzling behavior still occurs: $ hg status ... File ".../mercurial/changelog.py", line 123, in __init__ revlog.revlog.__init__(self, opener, "00changelog.i") File ".../mercurial/revlog.py", line 251, in __init__ d = self._io.parseindex(i, self._inline) File ".../mercurial/revlog.py", line 158, in parseindex index, cache = parsers.parse_index2(data, inline) TypeError: data is not a string which can be reproduced more simply with: import mercurial.parsers as parsers parsers.parse_index2("", True) Both the crash and the TypeError occurred because the Python C API's PyString_Check returns the wrong value when the C header files from Python 2.7 are run with Python 2.5. This is an example of an incompatibility of the sort mentioned in the Python bug report above. Failing fast with an informative error message will result in a better user experience in cases like the above. The information in the ImportError will also simplify troubleshooting for those on Mercurial mailing lists, the bug tracker, etc. This patch only adds the version check to parsers.c, which is sufficient to affect command-line commands like "hg status" and "hg summary". An idea for a future improvement is to move the version-checking C code to a more central location, and have it run when importing all Mercurial extension modules and not just parsers.c.
author Chris Jerdonek <chris.jerdonek@gmail.com>
date Fri, 29 Nov 2013 12:36:28 -0800
parents db0f8738d3d4
children 28fe5abc906f
files mercurial/parsers.c tests/test-parseindex2.py
diffstat 2 files changed, 80 insertions(+), 0 deletions(-) [+]
line wrap: on
line diff
--- a/mercurial/parsers.c	Wed Nov 27 16:43:02 2013 -0500
+++ b/mercurial/parsers.c	Fri Nov 29 12:36:28 2013 -0800
@@ -1941,6 +1941,25 @@
 	dirstate_unset = Py_BuildValue("ciii", 'n', 0, -1, -1);
 }
 
+static int check_python_version()
+{
+	PyObject *sys = PyImport_ImportModule("sys");
+	PyObject *hexversion = PyObject_GetAttrString(sys, "hexversion");
+	long version = PyInt_AsLong(hexversion);
+	/* sys.hexversion is a 32-bit number by default, so the -1 case
+	 * should only occur in unusual circumstances (e.g. if sys.hexversion
+	 * is manually set to an invalid value). */
+	if ((version == -1) || (version >> 16 != PY_VERSION_HEX >> 16)) {
+		PyErr_Format(PyExc_ImportError, "Python minor version mismatch: "
+			"The Mercurial extension modules were compiled with Python "
+			PY_VERSION ", but Mercurial is currently using Python with "
+			"sys.hexversion=%ld: Python %s\n at: %s", version,
+			Py_GetVersion(), Py_GetProgramFullPath());
+		return -1;
+	}
+	return 0;
+}
+
 #ifdef IS_PY3K
 static struct PyModuleDef parsers_module = {
 	PyModuleDef_HEAD_INIT,
@@ -1952,6 +1971,8 @@
 
 PyMODINIT_FUNC PyInit_parsers(void)
 {
+	if (check_python_version() == -1)
+		return;
 	PyObject *mod = PyModule_Create(&parsers_module);
 	module_init(mod);
 	return mod;
@@ -1959,6 +1980,8 @@
 #else
 PyMODINIT_FUNC initparsers(void)
 {
+	if (check_python_version() == -1)
+		return;
 	PyObject *mod = Py_InitModule3("parsers", methods, parsers_doc);
 	module_init(mod);
 }
--- a/tests/test-parseindex2.py	Wed Nov 27 16:43:02 2013 -0500
+++ b/tests/test-parseindex2.py	Fri Nov 29 12:36:28 2013 -0800
@@ -1,6 +1,8 @@
 from mercurial import parsers
 from mercurial.node import nullid, nullrev
 import struct
+import subprocess
+import sys
 
 # This unit test compares the return value of the original Python
 # implementation of parseindex and the new C implementation for
@@ -97,7 +99,62 @@
     index, chunkcache = parsers.parse_index2(data, inline)
     return list(index), chunkcache
 
+def importparsers(hexversion):
+    """Import mercurial.parsers with the given sys.hexversion."""
+    # The file parsers.c inspects sys.hexversion to determine the version
+    # of the currently-running Python interpreter, so we monkey-patch
+    # sys.hexversion to simulate using different versions.
+    code = ("import sys; sys.hexversion=%s; "
+            "import mercurial.parsers" % hexversion)
+    cmd = "python -c \"%s\"" % code
+    # We need to do these tests inside a subprocess because parser.c's
+    # version-checking code happens inside the module init function, and
+    # when using reload() to reimport an extension module, "The init function
+    # of extension modules is not called a second time"
+    # (from http://docs.python.org/2/library/functions.html?#reload).
+    p = subprocess.Popen(cmd, shell=True,
+                         stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+    return p.communicate()  # returns stdout, stderr
+
+def printhexfail(testnumber, hexversion, msg):
+    try:
+        hexstring = hex(hexversion)
+    except TypeError:
+        hexstring = None
+    print ("%s) using Python %s and patched sys.hexversion %r (%r): %s" %
+           (testnumber, sys.version_info, hexversion, hexstring, msg))
+
+def testversionokay(testnumber, hexversion):
+    stdout, stderr = importparsers(hexversion)
+    if stdout:
+        printhexfail(testnumber, hexversion,
+                     "Expected no stdout but got: %r" % stdout)
+
+def testversionfail(testnumber, hexversion):
+    stdout, stderr = importparsers(hexversion)
+    if not "ImportError: Python minor version mismatch" in stdout:
+        printhexfail(testnumber, hexversion,
+                     "Expected stdout to contain %r but got: %r" %
+                     (errstring, stdout))
+
+def makehex(major, minor, micro):
+    return int("%x%02x%02x00" % (major, minor, micro), 16)
+
+def runversiontests():
+    """Test importing parsers using different Python versions."""
+    info = sys.version_info
+    major, minor, micro = info[0], info[1], info[2]
+    # Test same major-minor versions.
+    testversionokay(1, makehex(major, minor, micro))
+    testversionokay(2, makehex(major, minor, micro + 1))
+    # Test different major-minor versions.
+    testversionfail(3, makehex(major + 1, minor, micro))
+    testversionfail(4, makehex(major, minor + 1, micro))
+    testversionfail(5, "'foo'")
+
 def runtest() :
+    runversiontests()
+
     # Check that parse_index2() raises TypeError on bad arguments.
     try:
         parse_index2(0, True)