Implement a `readonly` mode

This commit introduces the `readonly` variable as well as the `-ro`
command line option which prevent buffers from being overwritten on
disk when the `write` command is used without arguments. Some buffers
can selectively be put in readonly mode by setting the `readonly`
variable on the `buffer` scope, the `global` mode will affect all
buffers (even those who will be open subsequently), using the `window`
scope will have no effect.

Closes #685

1 files changed, 7 insertions, 0 deletions

diff --git a/src/buffer.cc b/src/buffer.cc
index 089103b1..f447f2db 100644
--- a/src/buffer.cc
+++ b/src/buffer.cc
@@ -591,6 +591,13 @@ void Buffer::set_fs_timestamp(timespec ts)
 
 void Buffer::on_option_changed(const Option& option)
 {
+    if (option.name() == "readonly")
+    {
+        if (option.get<bool>())
+            m_flags |= Flags::ReadOnly;
+        else
+            m_flags &= ~Flags::ReadOnly;
+    }
     run_hook_in_own_context("BufSetOption",
                             format("{}={}", option.name(), option.get_as_string()));
 }