Handling of non-words in publisher query

[kelson42]

The approach used in publisherQuery() for building a phrase query
enforcing the specified prefix for all terms fails if the input phrase
contains a term that Xapian's query parser doesn't like (e.g. a
standalone ampersand character, 1/2, a#1, etc).

Using the quest tool (coming with xapian-tools under Ubuntu) the
issue can be demonstrated as follows:

$ quest -o phrase -d some_xapian_db "Energy & security act"
UnimplementedError: OP_NEAR and OP_PHRASE only currently support leaf subqueries

$ quest -o phrase -d some_xapian_db 'Energy 1/2 security act'
UnimplementedError: OP_NEAR and OP_PHRASE only currently support leaf subqueries

$ quest -o phrase -d some_xapian_db "Energy a#1 security act"
UnimplementedError: OP_NEAR and OP_PHRASE only currently support leaf subqueries

The problem comes from parsing the query with the default operation set
to OP_PHRASE (exemplified by the -o phrase option in above
invocations of quest). A workaround is to parse the phrase with a
default operation of OP_OR and then combine all the terms with
OP_PHRASE.

This issue is likely to be present in libzim/src/search.cpp too, where
set_default_op(Xapian::Query::op::OP_PHRASE) is used. It affects
suggestions in my local build of kiwix-serve (though the instance
running at library.kiwix.org seems to be unaffected, is it an old
version?).

[kelson42]

Duplicate of #536

[veloman-yunkan]

@kelson42 I don't see why you had to open this issue in libzim and then close it as a duplicate for #536. This bug was introduced and then fixed in the yet umerged PR kiwix/libkiwix#488. The only relation of that virtual issue to libzim is that an approach from libzim source code was utilized in new code added to kiwix-lib. The only thing that has to be done about that yet unmerged piece of code in kiwix-lib is to incorporate the extra fix (disabling of stemming) that @maneeshpm has done in #534.

[kelson42]

@veloman-yunkan I got confused, but to avoid any confusion in the future please always open a bug ticket before a fixing PR.