Handle patches with misformatted empty lines

Insert a space on empty lines which are missing a control character.

Signed-off-by: Hollis Blanchard <[e-mail]>
---
I frequently receive emailed patches with empty lines represented as "\n\n",
where Mercurial expects them to be "\n \n". patch(1) applies these patches
without complaint, but qpush fails all hunks.

mercurial/diffhelpers.c

@@ -1,150 +1,156 b''
 /*
  * diffhelpers.c - helper routines for mpatch
  *
  * Copyright 2007 Chris Mason <[e-mail]>
  *
  * This software may be used and distributed according to the terms
  * of the GNU General Public License v2, incorporated herein by reference.
  */
 
 #include <Python.h>
 #include <stdlib.h>
 #include <string.h>
 
 static char diffhelpers_doc[] = "Efficient diff parsing";
 static PyObject *diffhelpers_Error;
 
 
 /* fixup the last lines of a and b when the patch has no newline at eof */
 static void _fix_newline(PyObject *hunk, PyObject *a, PyObject *b)
 {
 	int hunksz = PyList_Size(hunk);
 	PyObject *s = PyList_GET_ITEM(hunk, hunksz-1);
 	char *l = PyString_AS_STRING(s);
 	int sz = PyString_GET_SIZE(s);
 	int alen = PyList_Size(a);
 	int blen = PyList_Size(b);
 	char c = l[0];
 
 	PyObject *hline = PyString_FromStringAndSize(l, sz-1);
 	if (c == ' ' || c == '+') {
 		PyObject *rline = PyString_FromStringAndSize(l+1, sz-2);
 		PyList_SetItem(b, blen-1, rline);
 	}
 	if (c == ' ' || c == '-') {
 		Py_INCREF(hline);
 		PyList_SetItem(a, alen-1, hline);
 	}
 	PyList_SetItem(hunk, hunksz-1, hline);
 }
 
 /* python callable form of _fix_newline */
 static PyObject *
 fix_newline(PyObject *self, PyObject *args)
 {
 	PyObject *hunk, *a, *b;
 	if (!PyArg_ParseTuple(args, "OOO", &hunk, &a, &b))
 		return NULL;
 	_fix_newline(hunk, a, b);
 	return Py_BuildValue("l", 0);
 }
 
 /*
  * read lines from fp into the hunk.  The hunk is parsed into two arrays
  * a and b.  a gets the old state of the text, b gets the new state
  * The control char from the hunk is saved when inserting into a, but not b
  * (for performance while deleting files)
  */
 static PyObject *
 addlines(PyObject *self, PyObject *args)
 {
 
 	PyObject *fp, *hunk, *a, *b, *x;
 	int i;
 	int lena, lenb;
 	int num;
 	int todoa, todob;
 	char *s, c;
 	PyObject *l;
 	if (!PyArg_ParseTuple(args, "OOiiOO", &fp, &hunk, &lena, &lenb, &a, &b))
 		return NULL;
 
 	while(1) {
 		todoa = lena - PyList_Size(a);
 		todob = lenb - PyList_Size(b);
 		num = todoa > todob ? todoa : todob;
 		if (num == 0)
 		    break;
 		for (i = 0 ; i < num ; i++) {
 			x = PyFile_GetLine(fp, 0);
 			s = PyString_AS_STRING(x);
 			c = *s;
 			if (strcmp(s, "\\ No newline at end of file\n") == 0) {
 				_fix_newline(hunk, a, b);
 				continue;
 			}
+			if (c == '\n') {
+				/* Some patches may be missing the control char
+				 * on empty lines. Supply a leading space. */
+				Py_DECREF(x);
+				x = PyString_FromString(" \n");
+			}
 			PyList_Append(hunk, x);
 			if (c == '+') {
 				l = PyString_FromString(s + 1);
 				PyList_Append(b, l);
 				Py_DECREF(l);
 			} else if (c == '-') {
 				PyList_Append(a, x);
 			} else {
 				l = PyString_FromString(s + 1);
 				PyList_Append(b, l);
 				Py_DECREF(l);
 				PyList_Append(a, x);
 			}
 			Py_DECREF(x);
 		}
 	}
 	return Py_BuildValue("l", 0);
 }
 
 /*
  * compare the lines in a with the lines in b.  a is assumed to have
  * a control char at the start of each line, this char is ignored in the
  * compare
  */
 static PyObject *
 testhunk(PyObject *self, PyObject *args)
 {
 
 	PyObject *a, *b;
 	long bstart;
 	int alen, blen;
 	int i;
 	char *sa, *sb;
 
 	if (!PyArg_ParseTuple(args, "OOl", &a, &b, &bstart))
 		return NULL;
 	alen = PyList_Size(a);
 	blen = PyList_Size(b);
 	if (alen > blen - bstart) {
 		return Py_BuildValue("l", -1);
 	}
 	for (i = 0 ; i < alen ; i++) {
 		sa = PyString_AS_STRING(PyList_GET_ITEM(a, i));
 		sb = PyString_AS_STRING(PyList_GET_ITEM(b, i + bstart));
 		if (strcmp(sa+1, sb) != 0)
 			return Py_BuildValue("l", -1);
 	}
 	return Py_BuildValue("l", 0);
 }
 
 static PyMethodDef methods[] = {
 	{"addlines", addlines, METH_VARARGS, "add lines to a hunk\n"},
 	{"fix_newline", fix_newline, METH_VARARGS, "fixup newline counters\n"},
 	{"testhunk", testhunk, METH_VARARGS, "test lines in a hunk\n"},
 	{NULL, NULL}
 };
 
 PyMODINIT_FUNC
 initdiffhelpers(void)
 {
 	Py_InitModule3("diffhelpers", methods, diffhelpers_doc);
 	diffhelpers_Error = PyErr_NewException("diffhelpers.diffhelpersError",
 	                                        NULL, NULL);
 }