From 6060c7444bf63e66a2a88e44815c872f21da3bcf Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sun, 17 May 2020 22:24:52 +0200
Subject: [PATCH] LibGUI: Fix crash in TextDocument::remove(TextRange)

Oops, we can't be appending substrings of a string we just deleted!

Fix this by building up the new line instead of trying to clear and
append in place. This works out nicely as we now do fewer document view
updates when removing a range. :^)
---
 Libraries/LibGUI/TextDocument.cpp | 15 ++++++++++++---
 Libraries/LibGUI/TextDocument.h   |  1 +
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/Libraries/LibGUI/TextDocument.cpp b/Libraries/LibGUI/TextDocument.cpp
index 32ba3a42355..b6d4ef34727 100644
--- a/Libraries/LibGUI/TextDocument.cpp
+++ b/Libraries/LibGUI/TextDocument.cpp
@@ -117,6 +117,12 @@ void TextDocumentLine::clear(TextDocument& document)
     document.update_views({});
 }
 
+void TextDocumentLine::set_text(TextDocument& document, const Vector<u32> text)
+{
+    m_text = move(text);
+    document.update_views({});
+}
+
 void TextDocumentLine::set_text(TextDocument& document, const StringView& text)
 {
     if (text.is_empty()) {
@@ -132,6 +138,8 @@ void TextDocumentLine::set_text(TextDocument& document, const StringView& text)
 
 void TextDocumentLine::append(TextDocument& document, const u32* codepoints, size_t length)
 {
+    if (length == 0)
+        return;
     m_text.append(codepoints, length);
     document.update_views({});
 }
@@ -588,9 +596,10 @@ void TextDocument::remove(const TextRange& unnormalized_range)
         ASSERT(range.start().line() == range.end().line() - 1);
         auto& first_line = line(range.start().line());
         auto& second_line = line(range.end().line());
-        first_line.clear(*this);
-        first_line.append(*this, first_line.codepoints(), range.start().column());
-        first_line.append(*this, second_line.codepoints() + range.end().column(), second_line.length() - range.end().column());
+        Vector<u32> codepoints;
+        codepoints.append(first_line.codepoints(), range.start().column());
+        codepoints.append(second_line.codepoints() + range.end().column(), second_line.length() - range.end().column());
+        first_line.set_text(*this, move(codepoints));
         remove_line(range.end().line());
     }
 
diff --git a/Libraries/LibGUI/TextDocument.h b/Libraries/LibGUI/TextDocument.h
index 53aed50f4d5..07a858624af 100644
--- a/Libraries/LibGUI/TextDocument.h
+++ b/Libraries/LibGUI/TextDocument.h
@@ -160,6 +160,7 @@ public:
     const u32* codepoints() const { return m_text.data(); }
     size_t length() const { return m_text.size(); }
     void set_text(TextDocument&, const StringView&);
+    void set_text(TextDocument&, Vector<u32>);
     void append(TextDocument&, u32);
     void prepend(TextDocument&, u32);
     void insert(TextDocument&, size_t index, u32);