The custom queries are configured in rebar.config via the tuple
{xref_queries, [{query(), query_result()},...]}. The implementation
passes the query() string to xref:q and compares the return value with
query_result(). It will result in an error if they do not match.
The following configuration, for example, is the same as running the
xref check undefined_function_calls. It additionally filters
ejabberd_logger:*_msg/4 from the result as these functions are generated
on execution by ejabberd and not available at compile time.
{xref_queries, [{"(XC - UC) || (XU - X - B -
(\"ejabberd_logger\":\".*_msg\"/\"4\"))",[]}]}.
This patch also modifies the build process of this package by running a
custom query instead of doing a diff against a static xref_warning file.
It is now possible to call rebar as:
rebar xref skip_app=Mod1,Mod2,...
This makes it easy to skip running xref on (e.g)
imported dependencies in your application.
The function rebar_utils:is_skipped_app/0 is added so
that other rebar commands may use it.
For parameterized modules, the beam code will have a compiler
generated new/1 and instance/1 function.
If while checking the beam, xref detects one of those is unused, the
rebars xref wrapper will try to find the location of the definition of
that function in the source code for the module (to give a more
specific warning to the user). Since the function was generated by the
compiler it does not actually exist in the source, and rebar crashes
at that stage. This patch works around that issue.
