ls-files: prevent prune_cache from overeagerly pruning submodules

Since (ae8d08242 pathspec: pass directory indicator to
match_pathspec_item()) the path matching logic has been able to cope
with submodules without needing to strip off a trailing slash if a path
refers to a submodule.

ls-files is the only caller of 'parse_pathspec()' which relies on the
behavior of the PATHSPEC_STRIP_SUBMODULE_SLASH_CHEAP flag because it
uses the result to construct a common prefix of all provided pathspecs
which is then used to prune the index of all entries which don't have
that prefix.  Since submodules entries in the index don't have a
trailing slash 'prune_cache()' will be overeager and prune a submodule
'sub' if the common prefix is 'sub/'.  To correct this behavior, only
prune entries which don't match up to, but not including, a trailing
slash of the common prefix.

This is in preparation to remove the
PATHSPEC_STRIP_SUBMODULE_SLASH_CHEAP flag in a later patch.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/ls-files.c

@@ -97,7 +97,7 @@ static void show_dir_entry(const char *tag, struct dir_entry *ent)
 {
 	int len = max_prefix_len;
 
-	if (len >= ent->len)
+	if (len > ent->len)
 		die("git ls-files: internal error - directory entry not superset of prefix");
 
 	if (!dir_path_match(ent, &pathspec, len, ps_matched))
@@ -238,7 +238,7 @@ static void show_ce_entry(const char *tag, const struct cache_entry *ce)
 		strbuf_addstr(&name, super_prefix);
 	strbuf_addstr(&name, ce->name);
 
-	if (len >= ce_namelen(ce))
+	if (len > ce_namelen(ce))
 		die("git ls-files: internal error - cache entry not superset of prefix");
 
 	if (recurse_submodules && S_ISGITLINK(ce->ce_mode) &&
@@ -403,6 +403,25 @@ static void prune_cache(const char *prefix, size_t prefixlen)
 	active_nr = last - pos;
 }
 
+static int get_common_prefix_len(const char *common_prefix)
+{
+	int common_prefix_len;
+
+	if (!common_prefix)
+		return 0;
+
+	common_prefix_len = strlen(common_prefix);
+
+	/*
+	 * If the prefix has a trailing slash, strip it so that submodules wont
+	 * be pruned from the index.
+	 */
+	if (common_prefix[common_prefix_len - 1] == '/')
+		common_prefix_len--;
+
+	return common_prefix_len;
+}
+
 /*
  * Read the tree specified with --with-tree option
  * (typically, HEAD) into stage #1 and then
@@ -624,8 +643,7 @@ int cmd_ls_files(int argc, const char **argv, const char *cmd_prefix)
 		    "--error-unmatch");
 
 	parse_pathspec(&pathspec, 0,
-		       PATHSPEC_PREFER_CWD |
-		       PATHSPEC_STRIP_SUBMODULE_SLASH_CHEAP,
+		       PATHSPEC_PREFER_CWD,
 		       prefix, argv);
 
 	/*
@@ -637,7 +655,9 @@ int cmd_ls_files(int argc, const char **argv, const char *cmd_prefix)
 		max_prefix = NULL;
 	else
 		max_prefix = common_prefix(&pathspec);
-	max_prefix_len = max_prefix ? strlen(max_prefix) : 0;
+	max_prefix_len = get_common_prefix_len(max_prefix);
+
+	prune_cache(max_prefix, max_prefix_len);
 
 	/* Treat unmatching pathspec elements as errors */
 	if (pathspec.nr && error_unmatch)
@@ -651,7 +671,6 @@ int cmd_ls_files(int argc, const char **argv, const char *cmd_prefix)
 	      show_killed || show_modified || show_resolve_undo))
 		show_cached = 1;
 
-	prune_cache(max_prefix, max_prefix_len);
 	if (with_tree) {
 		/*
 		 * Basic sanity check; show-stages and show-unmerged