bug#38575: 27.0.50; Document that `diff' arguments OLD and NEW can be buffers

[Phil Sainty]

On 12/12/19 10:21 PM, Eli Zaretskii wrote:
>> I suggest the following additional paragraph:
>>
>>      Non-interactively, OLD and NEW may each be buffers, in which
>>      case a temporary file will be used.
> 
> Why is it important to mention the fact that we use temporary files
> in this case?  It sounds like an implementation detail.

It is, but I think it's a helpful detail to include, to eliminate
potential confusion regarding how a buffer can be a valid input, when
the rest of the description is about files.

The user might otherwise wonder whether Emacs is actually using the
external diff program in this case (vs using some internal functions
to process the buffer text directly to produce a diff).

I'm ok with omitting it if you're not convinced.


-Phil