Set the major mode of a new buffer interactively

Question

When creating a new buffer via:

1. C-x b
2. NonExistentBufferName RET RET

I would like Emacs to ask me what major mode this buffer is going to use upon opening. Moreover, I want Emacs to infer the major mode in some cases based on the buffer's name:

1. C-x b
2. test.org(no such buffer so far) RET RET => org-mode is used without asking me anything.

Could anybody advice if I can use any package for this? Or is it achievable at all via pure elisp?

P.S. I'm using ido if it matters.

Answer 1

Add entries in the magic-mode-alist/auto-mode-alist (in your init file most likely) if you want emacs to automatically determine major mode from buffer/file names (C-h v auto-mode-alist for info).

To interactively set the major mode just use M-x <mode-name, eg. c-mode>.

If you actually want emacs to interactively prompt you for a major mode every time you open a buffer, that could be achieved via a small advice to function you use to visit files (the ido functions in your case).