Refuse modification of ReadOnly buffers and make Debug buffer readonly

The debug buffer is a bit special as lots of events might mutate it,
permitting it to be modified leads to some buggy behaviour:

For example, `pipe` uses a ForwardChangeTracker to track buffer
changes, but when applied on a debug buffer with the profile flag
on, each shell execution will trigger an additional modification
of the buffer while applying the changes, leading to an assertion
failing as changes might not be happening in a forward way anymore.

Trying to modify a debug buffer will now raise an error immediatly.

src/buffer.cc

@@ -158,6 +158,12 @@ bool Buffer::set_name(String name)
     return false;
 }
 
+void Buffer::throw_if_read_only() const
+{
+    if (m_flags & Flags::ReadOnly)
+        throw runtime_error("Buffer is read-only");
+}
+
 void Buffer::update_display_name()
 {
     if (m_flags & Flags::File)
@@ -315,8 +321,10 @@ void Buffer::commit_undo_group()
     m_history_cursor = node;
 }
 
-bool Buffer::undo(size_t count) noexcept
+bool Buffer::undo(size_t count)
 {
+    throw_if_read_only();
+
     commit_undo_group();
 
     if (not m_history_cursor->parent)
@@ -333,8 +341,10 @@ bool Buffer::undo(size_t count) noexcept
     return true;
 }
 
-bool Buffer::redo(size_t count) noexcept
+bool Buffer::redo(size_t count)
 {
+    throw_if_read_only();
+
     if (not m_history_cursor->redo_child)
         return false;
 
@@ -350,8 +360,10 @@ bool Buffer::redo(size_t count) noexcept
     return true;
 }
 
-void Buffer::move_to(HistoryNode* history_node) noexcept
+void Buffer::move_to(HistoryNode* history_node)
 {
+    throw_if_read_only();
+
     commit_undo_group();
 
     auto find_lowest_common_parent = [](HistoryNode* a, HistoryNode* b) {
@@ -419,7 +431,7 @@ Buffer::HistoryNode* Buffer::find_history_node(HistoryNode* node, const Func& fu
     return nullptr;
 }
 
-bool Buffer::move_to(size_t history_id) noexcept
+bool Buffer::move_to(size_t history_id)
 {
     auto* target_node = find_history_node(&m_history, [history_id](auto* node)
                                           { return node->id == history_id; });
@@ -548,6 +560,8 @@ void Buffer::apply_modification(const Modification& modification)
 
 BufferCoord Buffer::insert(BufferCoord pos, StringView content)
 {
+    throw_if_read_only();
+
     kak_assert(is_valid(pos));
     if (content.empty())
         return pos;
@@ -568,6 +582,8 @@ BufferCoord Buffer::insert(BufferCoord pos, StringView content)
 
 BufferCoord Buffer::erase(BufferCoord begin, BufferCoord end)
 {
+    throw_if_read_only();
+
     kak_assert(is_valid(begin) and is_valid(end));
     // do not erase last \n except if we erase from the start of a line, and normalize
     // end coord
@@ -585,6 +601,8 @@ BufferCoord Buffer::erase(BufferCoord begin, BufferCoord end)
 
 BufferCoord Buffer::replace(BufferCoord begin, BufferCoord end, StringView content)
 {
+    throw_if_read_only();
+
     if (is_end(end) and not content.empty() and content.back() == '\n')
     {
         end = back_coord();

src/buffer.hh

@@ -139,9 +139,9 @@ public:
     void           set_fs_timestamp(timespec ts);
 
     void           commit_undo_group();
-    bool           undo(size_t count = 1) noexcept;
-    bool           redo(size_t count = 1) noexcept;
-    bool           move_to(size_t history_id) noexcept;
+    bool           undo(size_t count = 1);
+    bool           redo(size_t count = 1);
+    bool           move_to(size_t history_id);
     size_t         current_history_id() const noexcept;
     size_t         next_history_id() const noexcept { return m_next_history_id; }
 
@@ -218,6 +218,7 @@ public:
     void on_registered();
     void on_unregistered();
 
+    void throw_if_read_only() const;
 private:
     void on_option_changed(const Option& option) override;
 
@@ -272,7 +273,7 @@ private:
     SafePtr<HistoryNode>  m_last_save_history_cursor;
     UndoGroup             m_current_undo_group;
 
-    void move_to(HistoryNode* history_node) noexcept;
+    void move_to(HistoryNode* history_node);
 
     template<typename Func> HistoryNode* find_history_node(HistoryNode* node, const Func& func);
 

src/buffer_utils.cc

@@ -181,12 +181,17 @@ void write_to_debug_buffer(StringView str)
     // where the user can put its cursor to scroll with new messages
     const bool eol_back = not str.empty() and str.back() == '\n';
     if (Buffer* buffer = BufferManager::instance().get_buffer_ifp(debug_buffer_name))
+    {
+        buffer->flags() &= ~Buffer::Flags::ReadOnly;
+        auto restore = on_scope_end([buffer] { buffer->flags() |= Buffer::Flags::ReadOnly; });
+
         buffer->insert(buffer->back_coord(), eol_back ? str : str + "\n");
+    }
     else
     {
         String line = str + (eol_back ? "\n" : "\n\n");
         BufferManager::instance().create_buffer(
-            debug_buffer_name.str(), Buffer::Flags::NoUndo | Buffer::Flags::Debug,
+            debug_buffer_name.str(), Buffer::Flags::NoUndo | Buffer::Flags::Debug | Buffer::Flags::ReadOnly,
             line, InvalidTime);
     }
 }

src/input_handler.cc

@@ -1061,6 +1061,8 @@ public:
                            context().hooks().run_hook("InsertIdle", "", context());
                        }}
     {
+        context().buffer().throw_if_read_only();
+
         last_insert().recording.set();
         last_insert().mode = mode;
         last_insert().keys.clear();
@@ -1068,11 +1070,6 @@ public:
         last_insert().count = count;
         context().hooks().run_hook("InsertBegin", "", context());
         prepare(mode, count);
-
-        if (context().has_client() and
-            context().options()["readonly"].get<bool>())
-            context().print_status({ "Warning: This buffer is readonly",
-                                     get_face("Error") });
     }
 
     void on_enabled() override