From e0d4cdc9a338ffa1d46385d3997bb214748aa259 Mon Sep 17 00:00:00 2001
From: Jakob Borg <jakob@kastelo.net>
Date: Thu, 30 Jan 2020 09:58:44 +0100
Subject: [PATCH] lib/ignore: Don't crash on empty patterns (fixes #6300)
 (#6301)

Instead of panicking when we try to look closer at the empty pattern,
return something like `invalid pattern "(?d)" in ignore file: missing
pattern`.
---
 lib/ignore/ignore.go      |  4 ++++
 lib/ignore/ignore_test.go | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/lib/ignore/ignore.go b/lib/ignore/ignore.go
index 7578446ba..cbc56b13d 100644
--- a/lib/ignore/ignore.go
+++ b/lib/ignore/ignore.go
@@ -422,6 +422,10 @@ func parseLine(line string) ([]Pattern, error) {
 		}
 	}
 
+	if line == "" {
+		return nil, errors.New("missing pattern")
+	}
+
 	if pattern.result.IsCaseFolded() {
 		line = strings.ToLower(line)
 	}
diff --git a/lib/ignore/ignore_test.go b/lib/ignore/ignore_test.go
index 462f88a31..1de1e305d 100644
--- a/lib/ignore/ignore_test.go
+++ b/lib/ignore/ignore_test.go
@@ -14,6 +14,7 @@ import (
 	"os"
 	"path/filepath"
 	"runtime"
+	"strings"
 	"testing"
 	"time"
 
@@ -1150,3 +1151,20 @@ func TestSkipIgnoredDirs(t *testing.T) {
 		t.Error("SkipIgnoredDirs should be true")
 	}
 }
+
+func TestEmptyPatterns(t *testing.T) {
+	// These patterns are all invalid and should be rejected as such (without panicking...)
+	tcs := []string{
+		"!",
+		"(?d)",
+		"(?i)",
+	}
+
+	for _, tc := range tcs {
+		m := New(fs.NewFilesystem(fs.FilesystemTypeFake, ""))
+		err := m.Parse(strings.NewReader(tc), ".stignore")
+		if err == nil {
+			t.Error("Should reject invalid pattern", tc)
+		}
+	}
+}