Re: xref and leaving "temporary" buffers open

[Dmitry Gutov]

On 07/25/2015 06:53 PM, martin rudalics wrote:

> All file visiting functions must be aware of it and take it out.  As far
> as implementation is concerned we have the usual two choices: Pass an
> extra argument (clean but costly) or bind some variable around the calls
> that visit the file in the background which is probably the way to go.

How about this:

(defvar-local buffer-hidden nil
  "When non-nil, this buffer is not returned by `buffer-list',
unless passed a non-nil INCLUDE-HIDDEN argument.")

(defvar-local buffer-hidden-last-access nil
"The time when this buffer was last accessed.")

(defun buffer-list (&optional frame include-hidden)

(defvar find-file-hidden nil
  "When non-nil, new file buffers are marked as hidden.
`find-file-noselect', when creating a new buffer, will set
`buffer-hidden' to t, and `buffer-hidden-last-access' to the
current time.
When it's nil, `find-file-noselect' will set `buffer-hidden' and
`buffer-hidden-last-accessed' to nil in the buffer it returns.")

`find-file-noselect' might also become a problem with large amounts of 
hidden buffers, because `find-buffer-visiting' iterates through all 
buffers (and thus is O(N)). Although we should see whether it's an 
actual problem in practice.

> The "*every* reasonable way" solution applies only where such
> customizations are cheap to implement and the behavior is not easily
> predictable.  As fas as querying the user for whether to revert buffers
> I see no problem in doing that.  Personally, I'd never opt for a
> solution where I'm asked for each file individually.  But the options
> "never auto-revert", "always auto-revert without asking" and "if at
> least one file is stale ask whether to auto-revert all" seem all pretty
> reasonable to me and I would probably try them out.

"never auto-revert" sounds like "always ask", but without the option 
"yes", because xref should abort in this case rather than return wrong 
results, and the user would have to be notified of that anyway. So that 
makes for two reasonable values, I think: "always revert" and "ask 
before reverting".

As long as a vague "Some buffers are out of date. Revert?" will suffice, 
that won't be a problem. Naming the first out-of-date buffer should also 
be always possible, but whether we'll be able to name them all, depends 
on the implementation of a given command.

> The least recently accessed ones, I suppose.  So somewhere we might want
> to maintain a timestamp of the least recently background access of these
> buffers.

The time when `find-file-noselect' was last called seems like a good 
approximation of the most recent access time.