Upgrade patch to detect hunks that start after a false start.

Imagine a hunk that starts with a blank line, but the site to patch starts
with two blank lines.  Before we'd read the first blank line, think it was the
start of the hunk and buffer it, read the second blank line, notice that it
didn't match the second line of the hunk, and discard _both_ buffered lines of
context (writing them to the output file) without checking that one of the
later context lines might have been the real start of the hunk.

Make it re-check the rest of the buffered context for matches each time it
discards a line of buffered context.

1 files changed, 51 insertions, 27 deletions

diff --git a/toys/patch.c b/toys/patch.c
index 10615e3e..41371a3e 100644
--- a/toys/patch.c
+++ b/toys/patch.c
@@ -52,7 +52,7 @@ DEFINE_GLOBALS(
 
 	struct double_list *plines, *flines;
 	long oldline, oldlen, newline, newlen, linenum;
-	int context, state, filein, fileout, filepatch;
+	int context, state, filein, fileout, filepatch, hunknum;
 	char *tempname, *oldname;
 )
 
@@ -66,9 +66,11 @@ static void do_line(void *data)
 	struct double_list *dlist = (struct double_list *)data;
 
 	if (TT.state && *dlist->data != TT.state)
-		fdprintf(TT.state == 2 ? 2: TT.fileout,
+		fdprintf(TT.state == 2 ? 2 : TT.fileout,
 			"%s\n", dlist->data+(TT.state>2 ? 1 : 0));
+
 	free(dlist->data);
+	free(data);
 }
 
 static void finish_oldfile(void)
@@ -81,7 +83,7 @@ static void fail_hunk(void)
 	if (!TT.plines) return;
 	TT.plines->prev->next = 0;
 
-	printf("Hunk FAILED.\n");
+	fdprintf(2, "Hunk %d FAILED.\n", TT.hunknum);
 	toys.exitval = 1;
 
 	// If we got to this point, we've seeked to the end.  Discard changes to
@@ -96,7 +98,7 @@ static void fail_hunk(void)
 
 static void apply_hunk(void)
 {
-	struct double_list *plist, *buf = NULL;
+	struct double_list *plist, *buf = NULL, *check;
 	int i = 0, backwards = 0, matcheof = 0,
 		reverse = toys.optflags & FLAG_REVERSE;
 
@@ -119,42 +121,62 @@ static void apply_hunk(void)
 	// Start of for loop
 	if (TT.context) for (;;) {
 		char *data = get_line(TT.filein);
+
 		TT.linenum++;
 
-		// Skip lines we'd add.
+		// Skip lines of the hunk we'd be adding.
 		while (plist && *plist->data == "+-"[reverse]) {
-			if (data && !backwards && !strcmp(data, plist->data+1)) {
-				backwards = 1;
-				fdprintf(2,"Possibly reversed hunk at %ld\n", TT.linenum);
-			}
+			if (data && !strcmp(data, plist->data+1)) {
+				if (++backwards == TT.context)
+					fdprintf(2,"Possibly reversed hunk %d at %ld\n",
+						TT.hunknum, TT.linenum);
+			} else backwards=0;
 			plist = plist->next;
 		}
 
+		// Is this EOF?
 		if (!data) {
-			// Matched EOF?
+			// Does this hunk need to match EOF?
 			if (!plist && matcheof) break;
-			// File ended before we found a home for this hunk?
+
+			// File ended before we found a place for this hunk.
 			fail_hunk();
 			goto done;
 		}
-		dlist_add(&buf, data);
-
-		if (!plist || strcmp(data, plist->data+1)) {     // Ignore whitespace?
-			// Match failed, hunk doesn't go here.  Flush accumulated buffer
-			// so far.
-
-			buf->prev->next = NULL;
-			TT.state = 1;
-			llist_free(buf, do_line);
-			buf = NULL;
-			plist = TT.plines;
-		} else {
-			// Match, advance plist.
-			plist = plist->next;
-			if (!plist && !matcheof) break;
+		check = dlist_add(&buf, data);
+
+		// todo: teach the strcmp() to ignore whitespace.
+
+		for (;;) {
+			// If we hit the end of a hunk that needed EOF and this isn't EOF,
+			// or next line doesn't match, flush first line of buffered data and
+			// recheck match until we find a new match or run out of buffer.
+	
+			if (!plist || strcmp(check->data, plist->data+1)) {
+				// First line isn't a match, write it out.
+				TT.state = 1;
+				check = llist_pop(&buf);
+				check->prev->next = buf;
+				buf->prev = check->prev;
+				do_line(check);
+				plist = TT.plines;
+
+				// Out of buffered lines?
+				if (check==buf) {
+					buf = 0;
+					break;
+				}
+				check = buf;
+			} else {
+				// This line matches.  Advance plist, detect successful match.
+				plist = plist->next;
+				if (!plist && !matcheof) goto out;
+				check = check->next;
+				if (check == buf) break;
+			}
 		}
 	}
-
+out:
 	// Got it.  Emit changed data.
 	TT.state = "-+"[reverse];
 	llist_free(TT.plines, do_line);
@@ -266,6 +288,7 @@ void patch_main(void)
 				TT.state = 1;
 				TT.context = 0;
 				TT.linenum = 0;
+				TT.hunknum = 0;
 			}
 
 		// Start a new hunk?
@@ -275,6 +298,7 @@ void patch_main(void)
 				&TT.oldlen, &TT.newline, &TT.newlen))
 		{
 			TT.context = 0;
+			TT.hunknum++;
 			TT.state = 2;
 			continue;
 		}