prep_exclude: remove the artificial PATH_MAX limit

This fixes a segfault in git-status with long paths on Windows,
where PATH_MAX is only 260.

This also fixes the problem of silently ignoring .gitignore if the
full path exceeds PATH_MAX. Now add_excludes_from_file() will report
if it gets ENAMETOOLONG.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

dir.c

@@ -799,12 +799,12 @@ static void prep_exclude(struct dir_struct *dir, const char *base, int baselen)
 	 */
 	while ((stk = dir->exclude_stack) != NULL) {
 		if (stk->baselen <= baselen &&
-		    !strncmp(dir->basebuf, base, stk->baselen))
+		    !strncmp(dir->basebuf.buf, base, stk->baselen))
 			break;
 		el = &group->el[dir->exclude_stack->exclude_ix];
 		dir->exclude_stack = stk->prev;
 		dir->exclude = NULL;
-		free((char *)el->src); /* see strdup() below */
+		free((char *)el->src); /* see strbuf_detach() below */
 		clear_exclude_list(el);
 		free(stk);
 		group->nr--;
@@ -814,8 +814,17 @@ static void prep_exclude(struct dir_struct *dir, const char *base, int baselen)
 	if (dir->exclude)
 		return;
 
+	/*
+	 * Lazy initialization. All call sites currently just
+	 * memset(dir, 0, sizeof(*dir)) before use. Changing all of
+	 * them seems lots of work for little benefit.
+	 */
+	if (!dir->basebuf.buf)
+		strbuf_init(&dir->basebuf, PATH_MAX);
+
 	/* Read from the parent directories and push them down. */
 	current = stk ? stk->baselen : -1;
+	strbuf_setlen(&dir->basebuf, current < 0 ? 0 : current);
 	while (current < baselen) {
 		struct exclude_stack *stk = xcalloc(1, sizeof(*stk));
 		const char *cp;
@@ -833,48 +842,47 @@ static void prep_exclude(struct dir_struct *dir, const char *base, int baselen)
 		stk->baselen = cp - base;
 		stk->exclude_ix = group->nr;
 		el = add_exclude_list(dir, EXC_DIRS, NULL);
-		memcpy(dir->basebuf + current, base + current,
-		       stk->baselen - current);
+		strbuf_add(&dir->basebuf, base + current, stk->baselen - current);
+		assert(stk->baselen == dir->basebuf.len);
 
 		/* Abort if the directory is excluded */
 		if (stk->baselen) {
 			int dt = DT_DIR;
-			dir->basebuf[stk->baselen - 1] = 0;
+			dir->basebuf.buf[stk->baselen - 1] = 0;
 			dir->exclude = last_exclude_matching_from_lists(dir,
-				dir->basebuf, stk->baselen - 1,
-				dir->basebuf + current, &dt);
-			dir->basebuf[stk->baselen - 1] = '/';
+				dir->basebuf.buf, stk->baselen - 1,
+				dir->basebuf.buf + current, &dt);
+			dir->basebuf.buf[stk->baselen - 1] = '/';
 			if (dir->exclude &&
 			    dir->exclude->flags & EXC_FLAG_NEGATIVE)
 				dir->exclude = NULL;
 			if (dir->exclude) {
-				dir->basebuf[stk->baselen] = 0;
 				dir->exclude_stack = stk;
 				return;
 			}
 		}
 
-		/* Try to read per-directory file unless path is too long */
-		if (dir->exclude_per_dir &&
-		    stk->baselen + strlen(dir->exclude_per_dir) < PATH_MAX) {
-			strcpy(dir->basebuf + stk->baselen,
-					dir->exclude_per_dir);
+		/* Try to read per-directory file */
+		if (dir->exclude_per_dir) {
 			/*
 			 * dir->basebuf gets reused by the traversal, but we
 			 * need fname to remain unchanged to ensure the src
 			 * member of each struct exclude correctly
 			 * back-references its source file.  Other invocations
 			 * of add_exclude_list provide stable strings, so we
-			 * strdup() and free() here in the caller.
+			 * strbuf_detach() and free() here in the caller.
 			 */
-			el->src = strdup(dir->basebuf);
-			add_excludes_from_file_to_list(dir->basebuf,
-					dir->basebuf, stk->baselen, el, 1);
+			struct strbuf sb = STRBUF_INIT;
+			strbuf_addbuf(&sb, &dir->basebuf);
+			strbuf_addstr(&sb, dir->exclude_per_dir);
+			el->src = strbuf_detach(&sb, NULL);
+			add_excludes_from_file_to_list(el->src, el->src,
+						       stk->baselen, el, 1);
 		}
 		dir->exclude_stack = stk;
 		current = stk->baselen;
 	}
-	dir->basebuf[baselen] = '\0';
+	strbuf_setlen(&dir->basebuf, baselen);
 }
 
 /*
@@ -1671,4 +1679,5 @@ void clear_directory(struct dir_struct *dir)
 		free(stk);
 		stk = prev;
 	}
+	strbuf_release(&dir->basebuf);
 }

dir.h

@@ -119,7 +119,7 @@ struct dir_struct {
 	 */
 	struct exclude_stack *exclude_stack;
 	struct exclude *exclude;
-	char basebuf[PATH_MAX];
+	struct strbuf basebuf;
 };
 
 /*