set-buffer-major-mode: how to use on buffer without file?

[Jean Louis]

I would like to set major mode for the buffer which only displays a
revision in a buffer without associated file. The buffer name may end
with let us say .scm for scheme or .org for Org mode, I would like to
invoke the major mode based on the file extension.

Maybe `set-buffer-major-mode' is right function?

Or maybe some other?

Jean