ignore: add test and adjust style and comment for dir with wildmatch

The previous commit left the comment referencing the earlier state of
the code, change it to explain the current logic. While here, change the
logic to avoid repeating the copy of the base pattern.

src/ignore.c

@@ -89,18 +89,20 @@ static int does_negate_rule(int *out, git_vector *rules, git_attr_fnmatch *match
 		}
 
 	/*
-	 * If we're dealing with a directory (which we know via the
-	 * strchr() check) we want to use 'dirname/<star>' as the
-	 * pattern so p_fnmatch() honours FNM_PATHNAME
+	 * When dealing with a directory, we add '/<star>' so
+	 * p_fnmatch() honours FNM_PATHNAME. Checking for LEADINGDIR
+	 * alone isn't enough as that's also set for nagations, so we
+	 * need to check that NEGATIVE is off.
 	 */
 		git_buf_clear(&buf);
 		if (rule->containing_dir) {
 			git_buf_puts(&buf, rule->containing_dir);
 		}
-		if (rule->flags & GIT_ATTR_FNMATCH_LEADINGDIR && !(rule->flags & GIT_ATTR_FNMATCH_NEGATIVE))
-			error = git_buf_printf(&buf, "%s/*", rule->pattern);
-		else
-			error = git_buf_puts(&buf, rule->pattern);
+
+		error = git_buf_puts(&buf, rule->pattern);
+
+		if ((rule->flags & (GIT_ATTR_FNMATCH_LEADINGDIR | GIT_ATTR_FNMATCH_NEGATIVE)) == GIT_ATTR_FNMATCH_LEADINGDIR)
+			error = git_buf_PUTS(&buf, "/*");
 
 		if (error < 0)
 			goto out;

tests/status/ignore.c

@@ -1022,3 +1022,20 @@ void test_status_ignore__negate_exact_previous(void)
 	cl_git_pass(git_ignore_path_is_ignored(&ignored, g_repo, ".buildpath"));
 	cl_assert_equal_i(1, ignored);
 }
+
+void test_status_ignore__negate_starstar(void)
+{
+    int ignored;
+
+    g_repo = cl_git_sandbox_init("empty_standard_repo");
+
+    cl_git_mkfile("empty_standard_repo/.gitignore",
+              "code/projects/**/packages/*\n"
+              "!code/projects/**/packages/repositories.config");
+
+    cl_git_pass(git_futils_mkdir_r("code/projects/foo/bar/packages", "empty_standard_repo", 0777));
+    cl_git_mkfile("empty_standard_repo/code/projects/foo/bar/packages/repositories.config", "");
+
+    cl_git_pass(git_ignore_path_is_ignored(&ignored, g_repo, "code/projects/foo/bar/packages/repositories.config"));
+    cl_assert_equal_i(0, ignored);
+}