Debug: add a write_debug function

write_debug writes in a Scratch buffer named '*debug*', so that debug
messages are accessibles from within kakoune

src/debug.cc

@@ -0,0 +1,27 @@
+#include "debug.hh"
+
+#include "assert.hh"
+#include "buffer_manager.hh"
+
+namespace Kakoune
+{
+
+static Buffer& get_or_create_debug_buffer()
+{
+    static const std::string debug_buffer_name("*debug*");
+    Buffer* buffer = BufferManager::instance().get_buffer(debug_buffer_name);
+
+    if (not buffer)
+        buffer = new Buffer(debug_buffer_name, Buffer::Type::Scratch);
+
+    assert(buffer);
+    return *buffer;
+}
+
+void write_debug(const std::string& str)
+{
+    Buffer& debug_buffer = get_or_create_debug_buffer();
+    debug_buffer.insert(debug_buffer.end(), str);
+}
+
+}

src/debug.hh

@@ -0,0 +1,13 @@
+#ifndef debug_hh_INCLUDED
+#define debug_hh_INCLUDED
+
+#include <string>
+
+namespace Kakoune
+{
+
+void write_debug(const std::string& str);
+
+}
+
+#endif // debug_hh_INCLUDED

src/main.cc

@@ -7,6 +7,7 @@
 #include "register_manager.hh"
 #include "selectors.hh"
 #include "assert.hh"
+#include "debug.hh"
 
 #include <unordered_map>
 #include <map>
@@ -568,6 +569,7 @@ int main(int argc, char* argv[])
             try
             {
                 char c = getch();
+                write_debug(std::string("key ") + c + '\n');
 
                 if (isdigit(c))
                     count = count * 10 + c - '0';