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completion behaviour (was: zsh-workers: zsh-3.1.5 released)

Zefram wrote:

> Sven: would you please update your completion patches, and post
> new versions based on vanilla 3.1.5.  Specifically, the patches for
> inclusive ORing, grouping of completions, and the configurable fuzziness
> of matching.  I like all of these features.

Before I start incorporating these things into 3.1.5 I'd like to ask a
few questions.

We had some discusssion about a new way to define completion behaviour 
which (seemingly) settled on: let's use shell functions and offer a
few new builtins. So, if I implement this, do we really want the
changes to compctl (note: I mean compctl, most of the changes in the
completion code itself would be used anyway) or should we leave
compctl alone and offer the new possibilities through the new way to
define completion behaviour, thereby giving some incentive to switch
to the new way?

Anyway, here is my suggestion for this new completion definition

We use zle widgets, probably a new kind of widgets that uses some more 
special variables, like:

  CMDSTR   - the name of the current command, with some special values
             it could be used for certain contexts (conditions, math
             expressions, ...)
  words    - the words of the current command (an array)
  CURWORD  - the number of the current word (for words[CURWORD])
  PREFIX   - the prefix of the current word
  SUFFIX   - ...
  NMATCHES - the number of matches produced so far

Of course, many more interesting things can be thought of.

Using a special widget for this ensures that we have a common wrapper
function in the C code that must be used. The new builtins can be
called only from  such a widget or functions called from it and in the 
C code this should make it possible to leave most of the completion
code unchanged (especially the allocation behaviour).

The general procedure would be to define such a completion widget that
serves as a kind of main loop, calls other functions to produce the
matches and finally decides what to do with the matches (listing,
inserting, ...)

To make the definition and calling of completion functions for certain
commands easier there could be a new builtin, say `compfunc':

  compfunc -a <func-name> <cmd-names-or-patterns ...>

    Makes <func-name> be called for the given command. <func-name> may 
    be one of a few special strings for replacing `compctl -C -T -D'.

  compfunc -d <cmd-names-or-patterns ...>

    Deletes definitions.

  compfunc -c [ <cmd-str> ]

    Makes all of the defined functions for $CMDSTR or the given
    <cmd-str> be called (this is most of the main loop of the current
    completion code). We could use the return code of the completion
    functions to decide whether more functions should be called or

  compfunc [ -L ]

    Lists the definitions, probably in a form that could be used in
    .zshrc or wherever.

For producing the actual matches there is another builtin, say
`compadd'. For simplicity we could make it use the same flags
`compctl' uses now, but without `-x', `+', and the like, i.e. only the 
simple match-producing flags. This would allow us to re-use most of
the code for compctl and since only the simple flags would be
supported, the irritating part of compctl would not be inherited.

On the other side we might wih to clean things up and make `compadd'
get new options for the things to produce. This could also be combined 
with a different way to handle control flags (-U, -q,
grouping,...). We could make these flags be used `from now on' and
probably have a way to save/restore the current set of control flags
(whose state would be stored together with the matches produced),
e.g. (in an easy-to-read syntax):

  compadd -push
  compadd -quote -suffix '/'
  compadd -files               # optional glob pattern here
  compadd -pop

I'm not quite sure which would be better. But of course it should be
possible to write some helper functions that offer one of the syntaxes 
and internally uses the other.

Probably the most important change would be how xor'ed completion,
extended completion, and the like are handled - using shell

Xor'ed completion is simple if we have the special variables mentioned 
above (or some way to get this information from the completion code):

  compadd ...                        # try to produce some matches
  if [[ $old -eq $NMATCHES ]] then   # this is the xor test
    compadd ...
                                     # more xor tests could be here

More interesting is the replacement for `compctl -x'. As Bart already
pointed out, we could use things like:

  if [[ "$words[CURWORD-1]" = "-I" ]] then
    compadd -W /usr/include -/

I.e. use the normal shell tests and the special variables. But there
is a problem with this: with compctl the `-x' - tests not only test
for a certain condition, but also report some information back,
namely: the length of an prefix that should be ignored in the
completion string and (with `r[a,b]') a restriction on the command
words that should be used with `compctl -L'. Both of them are
important to have and aren't that easy to do by hand, so we might want 
to add a builtin for testing, say `comptest' that has options for the
different tests and automatically makes the completion code use the
resulting restrictions. Since these restrictions should be used only
for some `compadd's, we would also need a way to switch back to the
original (or previous) state, e.g.:

  if comptest -suffix '-'; then      # makes `-' be ignored
    compadd ...
    comptest -fin                    # old state again

Alternatively we could have a option meaning: activate the
restrictions resulting from the last test.

Finally we would need a way to insert the matches or the unambiguous
string for normal completion in the line. Since we are in a zle widget 
we could just add a way to get the prefix/suffix to insert from the
completion code and than fiddle with [LR]BUFFER (there is a problem
with automatically removable suffixes).

So we might add a builtin to control all this, e.g.:

  complist -i [ <number> ]

    The first effect of this is that the completion code calculates
    the things the user might want to insert. Without argument this
    inserts the unambiguous string, with argument it inserts the
    <number>'th match (this is needed to implement the menu-completion

  complist -k

    This notifies the completion code that the list of matches is to
    be kept so that the next invocation of the completion widget can
    test if there is still a valid list of matches and then continue

  complist -c

    This is the counterpart of `-k'. If the completion widget still
    has a a valid list but the completion string has changed we need
    to clear the list so that we can produce the matches for the new

`complist' should also offer ways to access some more information,
especially we need a way to decide if the recexact and listambiguous
behaviour should be emulated.

Finally we need a way to make the completion code list the matches
found. This could be done with `complist' or by using the return code
of the completion widget.

Some final remarks:

- Using special variables isn't necessary, we could offer a way to
  make the information be stored in some variables with use-supplied
  names (and partially we already have this, of course).
- The new builtins may have different names and options. Also I'd like 
  to think about combining soome of the builtins.
- The matching control could be improved, too (not only the syntax ;-). 
  We might have a builtin/optio to some builtin for defining sets of
  matching controls under a user-supplied name and a flag to `compadd' 
  that uses these names.
- Using shell functions may also be a first step in supporting
  higher-level descriptions, e.g.:

    function opt-arg() {
      [[ "$words[CURWORD-1]" = "$1" ]] && compadd "$argv[2,-1]"

  With that we could make paths in `/usr/include' after `-I' be
  completed with: 

    opt-arg -I -W /usr/include -/

So, now I would like to read some comments about all this ;-)


Sven Wischnowsky                         wischnow@xxxxxxxxxxxxxxxxxxxxxxx

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