lazymanifest: avoid reading uninitialized memory

I got errors running tests with clang UBSAN [1] enabled. One of them is:

```
--- test-dirstate.t
+++ test-dirstate.t.err
@@ -85,9 +85,115 @@
   $ echo "[extensions]" >> .hg/hgrc
   $ echo "dirstateex=../dirstateexception.py" >> .hg/hgrc
   $ hg up 0
-  abort: simulated error while recording dirstateupdates
-  [255]
+  mercurial/cext/manifest.c:781:13: runtime error: load of value 190, which is not a valid value for type 'bool'
+       #0 0x7f668a8cf748 in lazymanifest_diff mercurial/cext/manifest.c:781
+       #1 0x7f6692fc1dc4 in call_function Python-2.7.11/Python/ceval.c:4350
+      .......
+  SUMMARY: UndefinedBehaviorSanitizer: invalid-bool-load mercurial/cext/manifest.c:781:13 in
+  [1]
   $ hg log -r . -T '{rev}\n'
   1
   $ hg status
-  ? a
```

While the code is not technically wrong, but switching the condition would
make clang UBSAN happy. So let's do it.

The uninitialized memory could come from, for example, `lazymanifest_copy`
allocates `self->maxlines` items but only writes the first `self->lines`
items.

[1]: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html

Test Plan:
Run `test-dirstate.t` with UBSAN and it no longer reports the issue.

Differential Revision: https://phab.mercurial-scm.org/D1948

mercurial/cext/manifest.c

@@ -1,941 +1,941
 /*
  * manifest.c - manifest type that does on-demand parsing.
  *
  * Copyright 2015, Google Inc.
  *
  * This software may be used and distributed according to the terms of
  * the GNU General Public License, incorporated herein by reference.
  */
 #include <Python.h>
 
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include "charencode.h"
 #include "util.h"
 
 #define DEFAULT_LINES 100000
 
 typedef struct {
 	char *start;
 	Py_ssize_t len; /* length of line including terminal newline */
 	char hash_suffix;
 	bool from_malloc;
 	bool deleted;
 } line;
 
 typedef struct {
 	PyObject_HEAD
 	PyObject *pydata;
 	line *lines;
 	int numlines; /* number of line entries */
 	int livelines; /* number of non-deleted lines */
 	int maxlines; /* allocated number of lines */
 	bool dirty;
 } lazymanifest;
 
 #define MANIFEST_OOM -1
 #define MANIFEST_NOT_SORTED -2
 #define MANIFEST_MALFORMED -3
 
 /* get the length of the path for a line */
 static size_t pathlen(line *l)
 {
 	return strlen(l->start);
 }
 
 /* get the node value of a single line */
 static PyObject *nodeof(line *l)
 {
 	char *s = l->start;
 	ssize_t llen = pathlen(l);
 	PyObject *hash = unhexlify(s + llen + 1, 40);
 	if (!hash) {
 		return NULL;
 	}
 	if (l->hash_suffix != '\0') {
 		char newhash[21];
 		memcpy(newhash, PyBytes_AsString(hash), 20);
 		Py_DECREF(hash);
 		newhash[20] = l->hash_suffix;
 		hash = PyBytes_FromStringAndSize(newhash, 21);
 	}
 	return hash;
 }
 
 /* get the node hash and flags of a line as a tuple */
 static PyObject *hashflags(line *l)
 {
 	char *s = l->start;
 	size_t plen = pathlen(l);
 	PyObject *hash = nodeof(l);
 
 	/* 40 for hash, 1 for null byte, 1 for newline */
 	size_t hplen = plen + 42;
 	Py_ssize_t flen = l->len - hplen;
 	PyObject *flags;
 	PyObject *tup;
 
 	if (!hash)
 		return NULL;
 	flags = PyBytes_FromStringAndSize(s + hplen - 1, flen);
 	if (!flags) {
 		Py_DECREF(hash);
 		return NULL;
 	}
 	tup = PyTuple_Pack(2, hash, flags);
 	Py_DECREF(flags);
 	Py_DECREF(hash);
 	return tup;
 }
 
 /* if we're about to run out of space in the line index, add more */
 static bool realloc_if_full(lazymanifest *self)
 {
 	if (self->numlines == self->maxlines) {
 		self->maxlines *= 2;
 		self->lines = realloc(self->lines, self->maxlines * sizeof(line));
 	}
 	return !!self->lines;
 }
 
 /*
  * Find the line boundaries in the manifest that 'data' points to and store
  * information about each line in 'self'.
  */
 static int find_lines(lazymanifest *self, char *data, Py_ssize_t len)
 {
 	char *prev = NULL;
 	while (len > 0) {
 		line *l;
 		char *next = memchr(data, '\n', len);
 		if (!next) {
 			return MANIFEST_MALFORMED;
 		}
 		next++; /* advance past newline */
 		if (!realloc_if_full(self)) {
 			return MANIFEST_OOM; /* no memory */
 		}
 		if (prev && strcmp(prev, data) > -1) {
 			/* This data isn't sorted, so we have to abort. */
 			return MANIFEST_NOT_SORTED;
 		}
 		l = self->lines + ((self->numlines)++);
 		l->start = data;
 		l->len = next - data;
 		l->hash_suffix = '\0';
 		l->from_malloc = false;
 		l->deleted = false;
 		len = len - l->len;
 		prev = data;
 		data = next;
 	}
 	self->livelines = self->numlines;
 	return 0;
 }
 
 static int lazymanifest_init(lazymanifest *self, PyObject *args)
 {
 	char *data;
 	Py_ssize_t len;
 	int err, ret;
 	PyObject *pydata;
 	if (!PyArg_ParseTuple(args, "S", &pydata)) {
 		return -1;
 	}
 	err = PyBytes_AsStringAndSize(pydata, &data, &len);
 
 	self->dirty = false;
 	if (err == -1)
 		return -1;
 	self->pydata = pydata;
 	Py_INCREF(self->pydata);
 	Py_BEGIN_ALLOW_THREADS
 	self->lines = malloc(DEFAULT_LINES * sizeof(line));
 	self->maxlines = DEFAULT_LINES;
 	self->numlines = 0;
 	if (!self->lines)
 		ret = MANIFEST_OOM;
 	else
 		ret = find_lines(self, data, len);
 	Py_END_ALLOW_THREADS
 	switch (ret) {
 	case 0:
 		break;
 	case MANIFEST_OOM:
 		PyErr_NoMemory();
 		break;
 	case MANIFEST_NOT_SORTED:
 		PyErr_Format(PyExc_ValueError,
 			     "Manifest lines not in sorted order.");
 		break;
 	case MANIFEST_MALFORMED:
 		PyErr_Format(PyExc_ValueError,
 			     "Manifest did not end in a newline.");
 		break;
 	default:
 		PyErr_Format(PyExc_ValueError,
 			     "Unknown problem parsing manifest.");
 	}
 	return ret == 0 ? 0 : -1;
 }
 
 static void lazymanifest_dealloc(lazymanifest *self)
 {
 	/* free any extra lines we had to allocate */
 	int i;
 	for (i = 0; i < self->numlines; i++) {
 		if (self->lines[i].from_malloc) {
 			free(self->lines[i].start);
 		}
 	}
 	if (self->lines) {
 		free(self->lines);
 		self->lines = NULL;
 	}
 	if (self->pydata) {
 		Py_DECREF(self->pydata);
 		self->pydata = NULL;
 	}
 	PyObject_Del(self);
 }
 
 /* iteration support */
 
 typedef struct {
 	PyObject_HEAD lazymanifest *m;
 	Py_ssize_t pos;
 } lmIter;
 
 static void lmiter_dealloc(PyObject *o)
 {
 	lmIter *self = (lmIter *)o;
 	Py_DECREF(self->m);
 	PyObject_Del(self);
 }
 
 static line *lmiter_nextline(lmIter *self)
 {
 	do {
 		self->pos++;
 		if (self->pos >= self->m->numlines) {
 			return NULL;
 		}
 		/* skip over deleted manifest entries */
 	} while (self->m->lines[self->pos].deleted);
 	return self->m->lines + self->pos;
 }
 
 static PyObject *lmiter_iterentriesnext(PyObject *o)
 {
 	size_t pl;
 	line *l;
 	Py_ssize_t consumed;
 	PyObject *ret = NULL, *path = NULL, *hash = NULL, *flags = NULL;
 	l = lmiter_nextline((lmIter *)o);
 	if (!l) {
 		goto done;
 	}
 	pl = pathlen(l);
 	path = PyBytes_FromStringAndSize(l->start, pl);
 	hash = nodeof(l);
 	consumed = pl + 41;
 	flags = PyBytes_FromStringAndSize(l->start + consumed,
 					   l->len - consumed - 1);
 	if (!path || !hash || !flags) {
 		goto done;
 	}
 	ret = PyTuple_Pack(3, path, hash, flags);
 done:
 	Py_XDECREF(path);
 	Py_XDECREF(hash);
 	Py_XDECREF(flags);
 	return ret;
 }
 
 #ifdef IS_PY3K
 #define LAZYMANIFESTENTRIESITERATOR_TPFLAGS Py_TPFLAGS_DEFAULT
 #else
 #define LAZYMANIFESTENTRIESITERATOR_TPFLAGS Py_TPFLAGS_DEFAULT \
 	| Py_TPFLAGS_HAVE_ITER
 #endif
 
 static PyTypeObject lazymanifestEntriesIterator = {
 	PyVarObject_HEAD_INIT(NULL, 0) /* header */
 	"parsers.lazymanifest.entriesiterator", /*tp_name */
 	sizeof(lmIter),                  /*tp_basicsize */
 	0,                               /*tp_itemsize */
 	lmiter_dealloc,                  /*tp_dealloc */
 	0,                               /*tp_print */
 	0,                               /*tp_getattr */
 	0,                               /*tp_setattr */
 	0,                               /*tp_compare */
 	0,                               /*tp_repr */
 	0,                               /*tp_as_number */
 	0,                               /*tp_as_sequence */
 	0,                               /*tp_as_mapping */
 	0,                               /*tp_hash */
 	0,                               /*tp_call */
 	0,                               /*tp_str */
 	0,                               /*tp_getattro */
 	0,                               /*tp_setattro */
 	0,                               /*tp_as_buffer */
 	LAZYMANIFESTENTRIESITERATOR_TPFLAGS, /* tp_flags */
 	"Iterator for 3-tuples in a lazymanifest.",  /* tp_doc */
 	0,                               /* tp_traverse */
 	0,                               /* tp_clear */
 	0,                               /* tp_richcompare */
 	0,                               /* tp_weaklistoffset */
 	PyObject_SelfIter,               /* tp_iter: __iter__() method */
 	lmiter_iterentriesnext,          /* tp_iternext: next() method */
 };
 
 static PyObject *lmiter_iterkeysnext(PyObject *o)
 {
 	size_t pl;
 	line *l = lmiter_nextline((lmIter *)o);
 	if (!l) {
 		return NULL;
 	}
 	pl = pathlen(l);
 	return PyBytes_FromStringAndSize(l->start, pl);
 }
 
 #ifdef IS_PY3K
 #define LAZYMANIFESTKEYSITERATOR_TPFLAGS Py_TPFLAGS_DEFAULT
 #else
 #define LAZYMANIFESTKEYSITERATOR_TPFLAGS Py_TPFLAGS_DEFAULT \
 	| Py_TPFLAGS_HAVE_ITER
 #endif
 
 static PyTypeObject lazymanifestKeysIterator = {
 	PyVarObject_HEAD_INIT(NULL, 0) /* header */
 	"parsers.lazymanifest.keysiterator", /*tp_name */
 	sizeof(lmIter),                  /*tp_basicsize */
 	0,                               /*tp_itemsize */
 	lmiter_dealloc,                  /*tp_dealloc */
 	0,                               /*tp_print */
 	0,                               /*tp_getattr */
 	0,                               /*tp_setattr */
 	0,                               /*tp_compare */
 	0,                               /*tp_repr */
 	0,                               /*tp_as_number */
 	0,                               /*tp_as_sequence */
 	0,                               /*tp_as_mapping */
 	0,                               /*tp_hash */
 	0,                               /*tp_call */
 	0,                               /*tp_str */
 	0,                               /*tp_getattro */
 	0,                               /*tp_setattro */
 	0,                               /*tp_as_buffer */
 	LAZYMANIFESTKEYSITERATOR_TPFLAGS, /* tp_flags */
 	"Keys iterator for a lazymanifest.",  /* tp_doc */
 	0,                               /* tp_traverse */
 	0,                               /* tp_clear */
 	0,                               /* tp_richcompare */
 	0,                               /* tp_weaklistoffset */
 	PyObject_SelfIter,               /* tp_iter: __iter__() method */
 	lmiter_iterkeysnext,             /* tp_iternext: next() method */
 };
 
 static lazymanifest *lazymanifest_copy(lazymanifest *self);
 
 static PyObject *lazymanifest_getentriesiter(lazymanifest *self)
 {
 	lmIter *i = NULL;
 	lazymanifest *t = lazymanifest_copy(self);
 	if (!t) {
 		PyErr_NoMemory();
 		return NULL;
 	}
 	i = PyObject_New(lmIter, &lazymanifestEntriesIterator);
 	if (i) {
 		i->m = t;
 		i->pos = -1;
 	} else {
 		Py_DECREF(t);
 		PyErr_NoMemory();
 	}
 	return (PyObject *)i;
 }
 
 static PyObject *lazymanifest_getkeysiter(lazymanifest *self)
 {
 	lmIter *i = NULL;
 	lazymanifest *t = lazymanifest_copy(self);
 	if (!t) {
 		PyErr_NoMemory();
 		return NULL;
 	}
 	i = PyObject_New(lmIter, &lazymanifestKeysIterator);
 	if (i) {
 		i->m = t;
 		i->pos = -1;
 	} else {
 		Py_DECREF(t);
 		PyErr_NoMemory();
 	}
 	return (PyObject *)i;
 }
 
 /* __getitem__ and __setitem__ support */
 
 static Py_ssize_t lazymanifest_size(lazymanifest *self)
 {
 	return self->livelines;
 }
 
 static int linecmp(const void *left, const void *right)
 {
 	return strcmp(((const line *)left)->start,
 		      ((const line *)right)->start);
 }
 
 static PyObject *lazymanifest_getitem(lazymanifest *self, PyObject *key)
 {
 	line needle;
 	line *hit;
 	if (!PyBytes_Check(key)) {
 		PyErr_Format(PyExc_TypeError,
 			     "getitem: manifest keys must be a string.");
 		return NULL;
 	}
 	needle.start = PyBytes_AsString(key);
 	hit = bsearch(&needle, self->lines, self->numlines, sizeof(line),
 		      &linecmp);
 	if (!hit || hit->deleted) {
 		PyErr_Format(PyExc_KeyError, "No such manifest entry.");
 		return NULL;
 	}
 	return hashflags(hit);
 }
 
 static int lazymanifest_delitem(lazymanifest *self, PyObject *key)
 {
 	line needle;
 	line *hit;
 	if (!PyBytes_Check(key)) {
 		PyErr_Format(PyExc_TypeError,
 			     "delitem: manifest keys must be a string.");
 		return -1;
 	}
 	needle.start = PyBytes_AsString(key);
 	hit = bsearch(&needle, self->lines, self->numlines, sizeof(line),
 		      &linecmp);
 	if (!hit || hit->deleted) {
 		PyErr_Format(PyExc_KeyError,
 			     "Tried to delete nonexistent manifest entry.");
 		return -1;
 	}
 	self->dirty = true;
 	hit->deleted = true;
 	self->livelines--;
 	return 0;
 }
 
 /* Do a binary search for the insertion point for new, creating the
  * new entry if needed. */
 static int internalsetitem(lazymanifest *self, line *new)
 {
 	int start = 0, end = self->numlines;
 	while (start < end) {
 		int pos = start + (end - start) / 2;
 		int c = linecmp(new, self->lines + pos);
 		if (c < 0)
 			end = pos;
 		else if (c > 0)
 			start = pos + 1;
 		else {
 			if (self->lines[pos].deleted)
 				self->livelines++;
 			if (self->lines[pos].from_malloc)
 				free(self->lines[pos].start);
 			start = pos;
 			goto finish;
 		}
 	}
 	/* being here means we need to do an insert */
 	if (!realloc_if_full(self)) {
 		PyErr_NoMemory();
 		return -1;
 	}
 	memmove(self->lines + start + 1, self->lines + start,
 		(self->numlines - start) * sizeof(line));
 	self->numlines++;
 	self->livelines++;
 finish:
 	self->lines[start] = *new;
 	self->dirty = true;
 	return 0;
 }
 
 static int lazymanifest_setitem(
 	lazymanifest *self, PyObject *key, PyObject *value)
 {
 	char *path;
 	Py_ssize_t plen;
 	PyObject *pyhash;
 	Py_ssize_t hlen;
 	char *hash;
 	PyObject *pyflags;
 	char *flags;
 	Py_ssize_t flen;
 	size_t dlen;
 	char *dest;
 	int i;
 	line new;
 	if (!PyBytes_Check(key)) {
 		PyErr_Format(PyExc_TypeError,
 			     "setitem: manifest keys must be a string.");
 		return -1;
 	}
 	if (!value) {
 		return lazymanifest_delitem(self, key);
 	}
 	if (!PyTuple_Check(value) || PyTuple_Size(value) != 2) {
 		PyErr_Format(PyExc_TypeError,
 			     "Manifest values must be a tuple of (node, flags).");
 		return -1;
 	}
 	if (PyBytes_AsStringAndSize(key, &path, &plen) == -1) {
 		return -1;
 	}
 
 	pyhash = PyTuple_GetItem(value, 0);
 	if (!PyBytes_Check(pyhash)) {
 		PyErr_Format(PyExc_TypeError,
 			     "node must be a 20-byte string");
 		return -1;
 	}
 	hlen = PyBytes_Size(pyhash);
 	/* Some parts of the codebase try and set 21 or 22
 	 * byte "hash" values in order to perturb things for
 	 * status. We have to preserve at least the 21st
 	 * byte. Sigh. If there's a 22nd byte, we drop it on
 	 * the floor, which works fine.
 	 */
 	if (hlen != 20 && hlen != 21 && hlen != 22) {
 		PyErr_Format(PyExc_TypeError,
 			     "node must be a 20-byte string");
 		return -1;
 	}
 	hash = PyBytes_AsString(pyhash);
 
 	pyflags = PyTuple_GetItem(value, 1);
 	if (!PyBytes_Check(pyflags) || PyBytes_Size(pyflags) > 1) {
 		PyErr_Format(PyExc_TypeError,
 			     "flags must a 0 or 1 byte string");
 		return -1;
 	}
 	if (PyBytes_AsStringAndSize(pyflags, &flags, &flen) == -1) {
 		return -1;
 	}
 	/* one null byte and one newline */
 	dlen = plen + 41 + flen + 1;
 	dest = malloc(dlen);
 	if (!dest) {
 		PyErr_NoMemory();
 		return -1;
 	}
 	memcpy(dest, path, plen + 1);
 	for (i = 0; i < 20; i++) {
 		/* Cast to unsigned, so it will not get sign-extended when promoted
 		 * to int (as is done when passing to a variadic function)
 		 */
 		sprintf(dest + plen + 1 + (i * 2), "%02x", (unsigned char)hash[i]);
 	}
 	memcpy(dest + plen + 41, flags, flen);
 	dest[plen + 41 + flen] = '\n';
 	new.start = dest;
 	new.len = dlen;
 	new.hash_suffix = '\0';
 	if (hlen > 20) {
 		new.hash_suffix = hash[20];
 	}
 	new.from_malloc = true;     /* is `start` a pointer we allocated? */
 	new.deleted = false;        /* is this entry deleted? */
 	if (internalsetitem(self, &new)) {
 		return -1;
 	}
 	return 0;
 }
 
 static PyMappingMethods lazymanifest_mapping_methods = {
 	(lenfunc)lazymanifest_size,             /* mp_length */
 	(binaryfunc)lazymanifest_getitem,       /* mp_subscript */
 	(objobjargproc)lazymanifest_setitem,    /* mp_ass_subscript */
 };
 
 /* sequence methods (important or __contains__ builds an iterator) */
 
 static int lazymanifest_contains(lazymanifest *self, PyObject *key)
 {
 	line needle;
 	line *hit;
 	if (!PyBytes_Check(key)) {
 		/* Our keys are always strings, so if the contains
 		 * check is for a non-string, just return false. */
 		return 0;
 	}
 	needle.start = PyBytes_AsString(key);
 	hit = bsearch(&needle, self->lines, self->numlines, sizeof(line),
 		      &linecmp);
 	if (!hit || hit->deleted) {
 		return 0;
 	}
 	return 1;
 }
 
 static PySequenceMethods lazymanifest_seq_meths = {
 	(lenfunc)lazymanifest_size, /* sq_length */
 	0, /* sq_concat */
 	0, /* sq_repeat */
 	0, /* sq_item */
 	0, /* sq_slice */
 	0, /* sq_ass_item */
 	0, /* sq_ass_slice */
 	(objobjproc)lazymanifest_contains, /* sq_contains */
 	0, /* sq_inplace_concat */
 	0, /* sq_inplace_repeat */
 };
 
 
 /* Other methods (copy, diff, etc) */
 static PyTypeObject lazymanifestType;
 
 /* If the manifest has changes, build the new manifest text and reindex it. */
 static int compact(lazymanifest *self)
 {
 	int i;
 	ssize_t need = 0;
 	char *data;
 	line *src, *dst;
 	PyObject *pydata;
 	if (!self->dirty)
 		return 0;
 	for (i = 0; i < self->numlines; i++) {
 		if (!self->lines[i].deleted) {
 			need += self->lines[i].len;
 		}
 	}
 	pydata = PyBytes_FromStringAndSize(NULL, need);
 	if (!pydata)
 		return -1;
 	data = PyBytes_AsString(pydata);
 	if (!data) {
 		return -1;
 	}
 	src = self->lines;
 	dst = self->lines;
 	for (i = 0; i < self->numlines; i++, src++) {
 		char *tofree = NULL;
 		if (src->from_malloc) {
 			tofree = src->start;
 		}
 		if (!src->deleted) {
 			memcpy(data, src->start, src->len);
 			*dst = *src;
 			dst->start = data;
 			dst->from_malloc = false;
 			data += dst->len;
 			dst++;
 		}
 		free(tofree);
 	}
 	Py_DECREF(self->pydata);
 	self->pydata = pydata;
 	self->numlines = self->livelines;
 	self->dirty = false;
 	return 0;
 }
 
 static PyObject *lazymanifest_text(lazymanifest *self)
 {
 	if (compact(self) != 0) {
 		PyErr_NoMemory();
 		return NULL;
 	}
 	Py_INCREF(self->pydata);
 	return self->pydata;
 }
 
 static lazymanifest *lazymanifest_copy(lazymanifest *self)
 {
 	lazymanifest *copy = NULL;
 	if (compact(self) != 0) {
 		goto nomem;
 	}
 	copy = PyObject_New(lazymanifest, &lazymanifestType);
 	if (!copy) {
 		goto nomem;
 	}
 	copy->numlines = self->numlines;
 	copy->livelines = self->livelines;
 	copy->dirty = false;
 	copy->lines = malloc(self->maxlines *sizeof(line));
 	if (!copy->lines) {
 		goto nomem;
 	}
 	memcpy(copy->lines, self->lines, self->numlines * sizeof(line));
 	copy->maxlines = self->maxlines;
 	copy->pydata = self->pydata;
 	Py_INCREF(copy->pydata);
 	return copy;
 nomem:
 	PyErr_NoMemory();
 	Py_XDECREF(copy);
 	return NULL;
 }
 
 static lazymanifest *lazymanifest_filtercopy(
 	lazymanifest *self, PyObject *matchfn)
 {
 	lazymanifest *copy = NULL;
 	int i;
 	if (!PyCallable_Check(matchfn)) {
 		PyErr_SetString(PyExc_TypeError, "matchfn must be callable");
 		return NULL;
 	}
 	/* compact ourselves first to avoid double-frees later when we
 	 * compact tmp so that it doesn't have random pointers to our
 	 * underlying from_malloc-data (self->pydata is safe) */
 	if (compact(self) != 0) {
 		goto nomem;
 	}
 	copy = PyObject_New(lazymanifest, &lazymanifestType);
 	if (!copy) {
 		goto nomem;
 	}
 	copy->dirty = true;
 	copy->lines = malloc(self->maxlines * sizeof(line));
 	if (!copy->lines) {
 		goto nomem;
 	}
 	copy->maxlines = self->maxlines;
 	copy->numlines = 0;
 	copy->pydata = self->pydata;
 	Py_INCREF(self->pydata);
 	for (i = 0; i < self->numlines; i++) {
 		PyObject *arglist = NULL, *result = NULL;
 		arglist = Py_BuildValue("(s)", self->lines[i].start);
 		if (!arglist) {
 			return NULL;
 		}
 		result = PyObject_CallObject(matchfn, arglist);
 		Py_DECREF(arglist);
 		/* if the callback raised an exception, just let it
 		 * through and give up */
 		if (!result) {
 			free(copy->lines);
 			Py_DECREF(self->pydata);
 			return NULL;
 		}
 		if (PyObject_IsTrue(result)) {
 			assert(!(self->lines[i].from_malloc));
 			copy->lines[copy->numlines++] = self->lines[i];
 		}
 		Py_DECREF(result);
 	}
 	copy->livelines = copy->numlines;
 	return copy;
 nomem:
 	PyErr_NoMemory();
 	Py_XDECREF(copy);
 	return NULL;
 }
 
 static PyObject *lazymanifest_diff(lazymanifest *self, PyObject *args)
 {
 	lazymanifest *other;
 	PyObject *pyclean = NULL;
 	bool listclean;
 	PyObject *emptyTup = NULL, *ret = NULL;
 	PyObject *es;
 	int sneedle = 0, oneedle = 0;
 	if (!PyArg_ParseTuple(args, "O!|O", &lazymanifestType, &other, &pyclean)) {
 		return NULL;
 	}
 	listclean = (!pyclean) ? false : PyObject_IsTrue(pyclean);
 	es = PyBytes_FromString("");
 	if (!es) {
 		goto nomem;
 	}
 	emptyTup = PyTuple_Pack(2, Py_None, es);
 	Py_DECREF(es);
 	if (!emptyTup) {
 		goto nomem;
 	}
 	ret = PyDict_New();
 	if (!ret) {
 		goto nomem;
 	}
 	while (sneedle != self->numlines || oneedle != other->numlines) {
 		line *left = self->lines + sneedle;
 		line *right = other->lines + oneedle;
 		int result;
 		PyObject *key;
 		PyObject *outer;
 		/* If we're looking at a deleted entry and it's not
 		 * the end of the manifest, just skip it. */
-		if (left->deleted && sneedle < self->numlines) {
+		if (sneedle < self->numlines && left->deleted) {
 			sneedle++;
 			continue;
 		}
-		if (right->deleted && oneedle < other->numlines) {
+		if (oneedle < other->numlines && right->deleted) {
 			oneedle++;
 			continue;
 		}
 		/* if we're at the end of either manifest, then we
 		 * know the remaining items are adds so we can skip
 		 * the strcmp. */
 		if (sneedle == self->numlines) {
 			result = 1;
 		} else if (oneedle == other->numlines) {
 			result = -1;
 		} else {
 			result = linecmp(left, right);
 		}
 		key = result <= 0 ?
 			PyBytes_FromString(left->start) :
 			PyBytes_FromString(right->start);
 		if (!key)
 			goto nomem;
 		if (result < 0) {
 			PyObject *l = hashflags(left);
 			if (!l) {
 				goto nomem;
 			}
 			outer = PyTuple_Pack(2, l, emptyTup);
 			Py_DECREF(l);
 			if (!outer) {
 				goto nomem;
 			}
 			PyDict_SetItem(ret, key, outer);
 			Py_DECREF(outer);
 			sneedle++;
 		} else if (result > 0) {
 			PyObject *r = hashflags(right);
 			if (!r) {
 				goto nomem;
 			}
 			outer = PyTuple_Pack(2, emptyTup, r);
 			Py_DECREF(r);
 			if (!outer) {
 				goto nomem;
 			}
 			PyDict_SetItem(ret, key, outer);
 			Py_DECREF(outer);
 			oneedle++;
 		} else {
 			/* file exists in both manifests */
 			if (left->len != right->len
 			    || memcmp(left->start, right->start, left->len)
 			    || left->hash_suffix != right->hash_suffix) {
 				PyObject *l = hashflags(left);
 				PyObject *r;
 				if (!l) {
 					goto nomem;
 				}
 				r = hashflags(right);
 				if (!r) {
 					Py_DECREF(l);
 					goto nomem;
 				}
 				outer = PyTuple_Pack(2, l, r);
 				Py_DECREF(l);
 				Py_DECREF(r);
 				if (!outer) {
 					goto nomem;
 				}
 				PyDict_SetItem(ret, key, outer);
 				Py_DECREF(outer);
 			} else if (listclean) {
 				PyDict_SetItem(ret, key, Py_None);
 			}
 			sneedle++;
 			oneedle++;
 		}
 		Py_DECREF(key);
 	}
 	Py_DECREF(emptyTup);
 	return ret;
 nomem:
 	PyErr_NoMemory();
 	Py_XDECREF(ret);
 	Py_XDECREF(emptyTup);
 	return NULL;
 }
 
 static PyMethodDef lazymanifest_methods[] = {
 	{"iterkeys", (PyCFunction)lazymanifest_getkeysiter, METH_NOARGS,
 	 "Iterate over file names in this lazymanifest."},
 	{"iterentries", (PyCFunction)lazymanifest_getentriesiter, METH_NOARGS,
 	 "Iterate over (path, nodeid, flags) tuples in this lazymanifest."},
 	{"copy", (PyCFunction)lazymanifest_copy, METH_NOARGS,
 	 "Make a copy of this lazymanifest."},
 	{"filtercopy", (PyCFunction)lazymanifest_filtercopy, METH_O,
 	 "Make a copy of this manifest filtered by matchfn."},
 	{"diff", (PyCFunction)lazymanifest_diff, METH_VARARGS,
 	 "Compare this lazymanifest to another one."},
 	{"text", (PyCFunction)lazymanifest_text, METH_NOARGS,
 	 "Encode this manifest to text."},
 	{NULL},
 };
 
 #ifdef IS_PY3K
 #define LAZYMANIFEST_TPFLAGS Py_TPFLAGS_DEFAULT
 #else
 #define LAZYMANIFEST_TPFLAGS Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_SEQUENCE_IN
 #endif
 
 static PyTypeObject lazymanifestType = {
 	PyVarObject_HEAD_INIT(NULL, 0) /* header */
 	"parsers.lazymanifest",                           /* tp_name */
 	sizeof(lazymanifest),                             /* tp_basicsize */
 	0,                                                /* tp_itemsize */
 	(destructor)lazymanifest_dealloc,                 /* tp_dealloc */
 	0,                                                /* tp_print */
 	0,                                                /* tp_getattr */
 	0,                                                /* tp_setattr */
 	0,                                                /* tp_compare */
 	0,                                                /* tp_repr */
 	0,                                                /* tp_as_number */
 	&lazymanifest_seq_meths,                          /* tp_as_sequence */
 	&lazymanifest_mapping_methods,                    /* tp_as_mapping */
 	0,                                                /* tp_hash */
 	0,                                                /* tp_call */
 	0,                                                /* tp_str */
 	0,                                                /* tp_getattro */
 	0,                                                /* tp_setattro */
 	0,                                                /* tp_as_buffer */
 	LAZYMANIFEST_TPFLAGS,                             /* tp_flags */
 	"TODO(augie)",                                    /* tp_doc */
 	0,                                                /* tp_traverse */
 	0,                                                /* tp_clear */
 	0,                                                /* tp_richcompare */
 	0,                                             /* tp_weaklistoffset */
 	(getiterfunc)lazymanifest_getkeysiter,                /* tp_iter */
 	0,                                                /* tp_iternext */
 	lazymanifest_methods,                             /* tp_methods */
 	0,                                                /* tp_members */
 	0,                                                /* tp_getset */
 	0,                                                /* tp_base */
 	0,                                                /* tp_dict */
 	0,                                                /* tp_descr_get */
 	0,                                                /* tp_descr_set */
 	0,                                                /* tp_dictoffset */
 	(initproc)lazymanifest_init,                      /* tp_init */
 	0,                                                /* tp_alloc */
 };
 
 void manifest_module_init(PyObject * mod)
 {
 	lazymanifestType.tp_new = PyType_GenericNew;
 	if (PyType_Ready(&lazymanifestType) < 0)
 		return;
 	Py_INCREF(&lazymanifestType);
 
 	PyModule_AddObject(mod, "lazymanifest",
 			   (PyObject *)&lazymanifestType);
 }