From 35e0f51672daaa679f965a95d109daaa4fece4ea Mon Sep 17 00:00:00 2001
From: Jan-Erik Rediger <janerik@fnordig.de>
Date: Mon, 9 Jan 2023 21:51:21 +0100
Subject: [PATCH] Handle empty documents.

Fixes #31
---
 src/lib.rs                  | 2 +-
 tests/empty_document.in.md  | 3 +++
 tests/empty_document.out.md | 2 ++
 tests/it.rs                 | 7 +++++++
 4 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 tests/empty_document.in.md
 create mode 100644 tests/empty_document.out.md

diff --git a/src/lib.rs b/src/lib.rs
index c4d11b1..958a2c9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -229,7 +229,7 @@ fn add_toc(content: &str, cfg: &Config) -> Result<String> {
         log::trace!("content_after_toc={:?}", content_after_toc);
         // Multiline markers might have consumed trailing newlines,
         // we ensure there's always one before the content.
-        let extra = if content_after_toc.as_bytes()[0] == b'\n' {
+        let extra = if content_after_toc.is_empty() || content_after_toc.as_bytes()[0] == b'\n' {
             ""
         } else {
             "\n"
diff --git a/tests/empty_document.in.md b/tests/empty_document.in.md
new file mode 100644
index 0000000..b5041f2
--- /dev/null
+++ b/tests/empty_document.in.md
@@ -0,0 +1,3 @@
+# Chapter 1
+
+<!-- toc -->
diff --git a/tests/empty_document.out.md b/tests/empty_document.out.md
new file mode 100644
index 0000000..6786da2
--- /dev/null
+++ b/tests/empty_document.out.md
@@ -0,0 +1,2 @@
+# Chapter 1
+
diff --git a/tests/it.rs b/tests/it.rs
index 474b2dc..7101ded 100644
--- a/tests/it.rs
+++ b/tests/it.rs
@@ -157,3 +157,10 @@ fn backslash_escapes() {
     // Backslash-escaped elements should still be escaped.
     assert_toc!("backslash_escapes");
 }
+
+#[test]
+fn empty_document() {
+    // Regression test #31
+    // Empty documents should not fail
+    assert_toc!("empty_document");
+}