Re: xref-find-matches and stuff

[Dmitry Gutov]

On 05/09/2015 03:58 PM, Vitalie Spinu wrote:

> It works for completion because you can reliably disambiguate from
> context which completion to use. C in C, Python in py, files in strings
> with "/" in them etc.

It's not always so simple:

- In some contexts, file paths can appear in the buffer outside of 
string literals. In sh-mode and eshell-mode, for instance, that is the 
rule rather than exception.

- Depending on the context, file paths may have different quoting rules. 
See `completion-table-with-quoting' and its uses for more context (I 
don't understand that area well myself).

Point is, while it's possible to provide the basic functionality without 
specializing, a perfect file completion is language and 
environment-dependent. So it's hard to serve with just one completion 
function.

> With xref context is often unrelated to where you
> want to jump and, thus, is orthogonal to the selection of the "best"
> backend.

Not that often. 95% of the time, I either jump to the thing at point (in 
the current project), or to a thing at least somewhat related to it: a 
caller, a callee, or simply a laterally related function in the same 
project or in one of its dependencies or dependants. The current project 
and its dependencies are usually possible to determine automatically.

> No. Major mode just defines one backend. The end user defines a list of
> backends to be used simultaneously.

Would the user even know which backends are possible to use, if the 
major mode doesn't add it to `xref-backends'?

By the way, the above is an example of "manual management of backends", 
which we've ostensibly agreed is undesirable. It may be good for a power 
user, but let's try to make things "just work" more often, for the 
average user.

>   > Multi-language projects are an interesting example. But if there are
>   > no references between the source file in different languages
>
> Yet another argument for prompting on M-. by default ;)

And prompt for the project to jump to, every time?

>   > Personally, I'd just make a "switch to another project" a separate
>   > step here.
>
> That's the same as picking a backend just before the jump. Could be, but
> I hope for a better UI.

Selecting from a list of project might be a more transparent choice for 
a user, rather than picking from a list of backends.

>   > It's not ideal, no argument here. However, being unavailable in
>   > buffers without TAGS, or in some languages, means it can be safely
>   > skipped in those circumstances.
>
> No, it cannot. That's the main point. If I am in a non-tagged file I
> still want to be able to jump to my tags.

This use case still could be served by an extra "switch to another 
project" step, I think.

> As an non-ideal alternative, yes. I might be quite happy with being able
> to rotate backends during the minibuffer completion.

To have this kind of capability could be fun, but I think the current 
completing-read interface is ill-suited for this. IOW, you'd have to 
start with writing a new completing-read-function (Helm might be a 
somewhat viable alternative, since it can already use several sources at 
a time, and displays the name of each in its buffer).