bug#20322: 25.0.50; indent-tabs-mode should default to nil

[Dmitry Gutov <dgutov@yandex.ru>]

On 04/14/2015 06:07 AM, Stefan Monnier wrote:

> There was probably a reason originally.  Nowadays, I think the main
> reason it's t is because there's no sufficiently good reason to change
> it (the hypothetical benefit of change will be smaller than the pain of
> having to suffer through too many people bitching at the change).

Let's do a trial in master, to see how much bitching this results in? :)

Consider this: when initially diving into Emacs (coming from some 
experience with two IDEs), I was learning how to configure indentation 
in different modes. The necessary steps were:

1) Find the variable `indent-tabs-mode'. See it doesn't help with the 
amount of indentation per level, keep looking. Same with `tab-width'.

2) Find the language-dependent variables (js-indent-level, 
css-indent-offset and c-basic-offset). It doesn't help that each one is 
named in a different fashion.

3) Notice that while it almost works like intended, sometimes you get 
tabs inserted. Go back to `indent-tabs-mode', put `(setq 
indent-tabs-mode nil)` in the init file, see that it doesn't help.

4) Find out about buffer-local-ness and `setq-default'. That finally 
does it.

The above steps required certain persistence.

> I.e. this is kind of like endianness.

One could say that about any variable with existing default value, no?

I think it's different enough: the current users should know pretty 
easily how to change it, whereas it's usually a bigger issue for 
newcomers.  Better defaults would result in a better initial experience 
bringing the adoption up somewhat; on the flip side, I can't imagine 
anyone quitting Emacs over this default value.

And since this value is not just a user preference (it's 
project-dependent), even those who prefer tabs have probably had to use 
a different value at some point. So they know what to change.