Buffer: stronger invariant, a buffer is never empty and all lines finish by '\n'

src/buffer.cc

@@ -30,9 +30,11 @@ Buffer::Buffer(String name, Type type,
       m_option_manager(GlobalOptionManager::instance())
 {
     BufferManager::instance().register_buffer(*this);
-    if (not initial_content.empty())
+    if (initial_content.back() != '\n')
+        initial_content += '\n';
     do_insert(begin(), std::move(initial_content));
 
+
     Editor editor_for_hooks(*this);
     Context context(editor_for_hooks);
     if (type == Type::NewFile)
@@ -219,10 +221,12 @@ void Buffer::reset_undo_data()
 void Buffer::check_invariant() const
 {
     BufferSize start = 0;
+    assert(not m_lines.empty());
     for (auto& line : m_lines)
     {
         assert(line.start == start);
         assert(line.length() > 0);
+        assert(line.content.back() == '\n');
         start += line.length();
     }
 }
@@ -349,16 +353,23 @@ void Buffer::apply_modification(const Modification& modification)
     }
 }
 
-void Buffer::insert(const BufferIterator& pos, const String& content)
+void Buffer::insert(BufferIterator pos, const String& content)
 {
     if (content.empty())
         return;
+
+    if (pos.is_end())
+        --pos;
+
     m_current_undo_group.emplace_back(Modification::Insert, pos, content);
     do_insert(pos, content);
 }
 
-void Buffer::erase(const BufferIterator& begin, const BufferIterator& end)
+void Buffer::erase(BufferIterator begin, BufferIterator end)
 {
+    if (end.is_end() and (begin.column() != 0 or begin.is_begin()))
+        --end;
+
     if (begin == end)
         return;
 

src/buffer.hh

@@ -111,8 +111,8 @@ public:
 
     Type type() const { return m_type; }
 
-    void insert(const BufferIterator& pos, const String& content);
+    void insert(BufferIterator pos, const String& content);
-    void erase(const BufferIterator& begin, const BufferIterator& end);
+    void erase(BufferIterator begin, BufferIterator end);
 
     void           begin_undo_group();
     void           end_undo_group();

src/file.cc

@@ -130,6 +130,10 @@ Buffer* create_buffer_from_file(const String& filename)
     option_manager.set_option("eolformat", Option(crlf ? "crlf" : "lf"));
     option_manager.set_option("BOM", Option(bom ? "utf-8" : "no"));
 
+    // if the file ended with a \n, remove the \n added by the buffer
+    if (*(buffer->end() - 2) == '\n')
+        buffer->erase(buffer->end() - 1, buffer->end());
+
     // it never happened, buffer always was like that
     buffer->reset_undo_data();