[PATCH v3 1/2] Allow git-apply to ignore the hunk headers (AKA recountdiff)

@@ -12,7 +12,7 @@ SYNOPSIS
 'git-apply' [--stat] [--numstat] [--summary] [--check] [--index]
 	  [--apply] [--no-add] [--build-fake-ancestor <file>] [-R | --reverse]
 	  [--allow-binary-replacement | --binary] [--reject] [-z]
-	  [-pNUM] [-CNUM] [--inaccurate-eof] [--cached]
+	  [-pNUM] [-CNUM] [--inaccurate-eof] [--recount] [--cached]
 	  [--whitespace=<nowarn|warn|fix|error|error-all>]
 	  [--exclude=PATH] [--verbose] [<patch>...]
 

@@ -169,6 +169,11 @@ behavior:
 	correctly. This option adds support for applying such patches by
 	working around this bug.
 
+--recount::
+	Do not trust the line counts in the hunk headers, but infer them
+	by inspecting the patch (e.g. after editing the patch without
+	adjusting the hunk headers appropriately).
+
 -v, --verbose::
 	Report progress to stderr. By default, only a message about the
 	current patch being applied will be printed. This option will cause

@@ -153,6 +153,7 @@ struct patch {
 	unsigned int is_binary:1;
 	unsigned int is_copy:1;
 	unsigned int is_rename:1;
+	unsigned int recount:1;
 	struct fragment *fragments;
 	char *result;
 	size_t resultsize;

@@ -882,6 +883,50 @@ static int parse_range(const char *line, int len, int offset, const char *expect
 	return offset + ex;
 }
 
+static int recount_diff(char *line, int size, struct fragment *fragment)
+{
+	int line_nr = 0;
+
+	if (size < 1)
+		return -1;
+
+	fragment->oldpos = 2;
+	fragment->oldlines = fragment->newlines = 0;
+
+	for (;;) {
+		int len = linelen(line, size);
+		size -= len;
+		line += len;
+
+		if (size < 1)
+			return 0;
+
+		switch (*line) {
+		case ' ': case '\n':
+			fragment->newlines++;
+			/* fall through */
+		case '-':
+			fragment->oldlines++;
+			break;
+		case '+':
+			fragment->newlines++;
+			if (line_nr == 0) {
+				fragment->leading = 1;
+				fragment->oldpos = 1;
+			}
+			fragment->trailing = 1;
+			break;
+		case '@':
+			return size < 3 || prefixcmp(line, "@@ ");
+		case 'd':
+			return size < 5 || prefixcmp(line, "diff ");
+		default:
+			return -1;
+		}
+		line_nr++;
+	}
+}
+
 /*
  * Parse a unified diff fragment header of the
  * form "@@ -a,b +c,d @@"

@@ -1013,6 +1058,9 @@ static int parse_fragment(char *line, unsigned long size,
 	offset = parse_fragment_header(line, len, fragment);
 	if (offset < 0)
 		return -1;
+	if (offset > 0 && patch->recount &&
+			recount_diff(line + offset, size - offset, fragment))
+		return -1;
 	oldlines = fragment->oldlines;
 	newlines = fragment->newlines;
 	leading = 0;

@@ -2912,7 +2960,8 @@ static void prefix_patches(struct patch *p)
 	}
 }
 
-static int apply_patch(int fd, const char *filename, int inaccurate_eof)
+static int apply_patch(int fd, const char *filename, int inaccurate_eof,
+		int recount)
 {
 	size_t offset;
 	struct strbuf buf;

@@ -2929,6 +2978,7 @@ static int apply_patch(int fd, const char *filename, int inaccurate_eof)
 
 		patch = xcalloc(1, sizeof(*patch));
 		patch->inaccurate_eof = inaccurate_eof;
+		patch->recount = recount;
 		nr = parse_chunk(buf.buf + offset, buf.len - offset, patch);
 		if (nr < 0)
 			break;

@@ -2998,6 +3048,7 @@ int cmd_apply(int argc, const char **argv, const char *unused_prefix)
 	int i;
 	int read_stdin = 1;
 	int inaccurate_eof = 0;
+	int recount = 0;
 	int errs = 0;
 	int is_not_gitdir;
 

@@ -3015,7 +3066,8 @@ int cmd_apply(int argc, const char **argv, const char *unused_prefix)
 		int fd;
 
 		if (!strcmp(arg, "-")) {
-			errs |= apply_patch(0, "<stdin>", inaccurate_eof);
+			errs |= apply_patch(0, "<stdin>", inaccurate_eof,
+					recount);
 			read_stdin = 0;
 			continue;
 		}

@@ -3118,6 +3170,10 @@ int cmd_apply(int argc, const char **argv, const char *unused_prefix)
 			inaccurate_eof = 1;
 			continue;
 		}
+		if (!strcmp(arg, "--recount")) {
+			recount = 1;
+			continue;
+		}
 		if (0 < prefix_length)
 			arg = prefix_filename(prefix, prefix_length, arg);
 

@@ -3126,12 +3182,12 @@ int cmd_apply(int argc, const char **argv, const char *unused_prefix)
 			die("can't open patch '%s': %s", arg, strerror(errno));
 		read_stdin = 0;
 		set_default_whitespace_mode(whitespace_option);
-		errs |= apply_patch(fd, arg, inaccurate_eof);
+		errs |= apply_patch(fd, arg, inaccurate_eof, recount);
 		close(fd);
 	}
 	set_default_whitespace_mode(whitespace_option);
 	if (read_stdin)
-		errs |= apply_patch(0, "<stdin>", inaccurate_eof);
+		errs |= apply_patch(0, "<stdin>", inaccurate_eof, recount);
 	if (whitespace_error) {
 		if (squelch_whitespace_errors &&
 		    squelch_whitespace_errors < whitespace_error) {