test-completion and hash-tables

[Luc Teirlinck]

`try-completion' and `all-completions' use `compare-strings' to compare
strings, in its case-sensitive or case-insensitive variant, depending
on `completion-ignore-case', independently of how the collection of
strings is specified (alist, list, obarray, hash-table, function).
However, when the collection of strings is specified as a hash-table,
then `test-completion' uses whichever test the hash-table uses and, in
particular, `completion-ignore-case' is ignored.

Which of the following possibilities applies?

1.  This is a bug.

2.  `test-completion' is only supposed to be used on the results of
    calling either `try-completion' or `all-completions'.  In all
    cases where I saw `test-completion' being used, this was the case.
    If so, there is no inconsistency, as even `eq' hash-tables will
    work.

3.  It is the job of the programmer passing the hash table to
    `test-completion' to make sure that the hash-table uses the correct
    test, that is, the version of compare-strings that is consistent
    with `completion-ignore-case'.

In cases (2) or (3), this should be clearly documented in
`(elisp)Basic Completion' as well as in the docstring of
`test-completion', which I could do.  But I am not sure which of 1--3
applies.

Sincerely,

Luc.