xref

#!/usr/bin/env escript


-mode(compile).


-define(CONSOLE(Fmt, Args), io:format(standard_error, Fmt, Args)).
-define(FMT(Fmt, Args), io_lib:format(Fmt, Args)).

main(_) ->
    %% Spin up xref
    {ok, _} = xref:start(xref),
    ok = xref:set_library_path(xref, code:get_path()),
    xref:set_default(xref, [{verbose, true}]),
    {ok, _} = xref:add_directory(xref, "ebin"),

    XrefChecks = [
        undefined_function_calls,
        undefined_functions,
        locals_not_used,
        exports_not_used,
        deprecated_function_calls,
        deprecated_functions
    ],

    lists:foreach(fun run_check/1, XrefChecks),

    stopped = xref:stop(xref).


run_check(XrefCheck) ->
    {ok, Results} = xref:analyze(xref, XrefCheck),
    FilteredResults = filter_xref_results(XrefCheck, Results),
    lists:foreach(fun(Res) ->
        display_xref_result(XrefCheck, Res)
    end, FilteredResults).


%%
%% Ignore behaviour functions, and explicitly marked functions
%%
%% Functions can be ignored by using
%% -ignore_xref([{F, A}, {M, F, A}...]).

get_xref_ignorelist(Mod, XrefCheck) ->
    %% Get ignore_xref attribute and combine them in one list
    Attributes =
        try
            Mod:module_info(attributes)
        catch
            _Class:_Error -> []
        end,

    IgnoreXref = keyall(ignore_xref, Attributes),

    BehaviourCallbacks = get_behaviour_callbacks(XrefCheck, Attributes),

    %% And create a flat {M,F,A} list
    lists:foldl(
      fun({F, A}, Acc) -> [{Mod,F,A} | Acc];
         ({M, F, A}, Acc) -> [{M,F,A} | Acc]
      end, [], lists:flatten([IgnoreXref, BehaviourCallbacks])).


keyall(Key, List) ->
    lists:flatmap(fun({K, L}) when Key =:= K -> L; (_) -> [] end, List).


get_behaviour_callbacks(exports_not_used, Attributes) ->
    [B:behaviour_info(callbacks) ||
        B <- keyall(behaviour, Attributes) ++ keyall(behavior, Attributes)];
get_behaviour_callbacks(_XrefCheck, _Attributes) ->
    [].


parse_xref_result({_, MFAt}) -> MFAt;
parse_xref_result(MFAt) -> MFAt.


filter_xref_results(XrefCheck, XrefResults) ->
    SearchModules = lists:usort(
                      lists:map(
                        fun({Mt,_Ft,_At}) -> Mt;
                           ({{Ms,_Fs,_As},{_Mt,_Ft,_At}}) -> Ms;
                           (_) -> undefined
                        end, XrefResults)),

    Ignores = lists:flatmap(fun(Module) ->
                                    get_xref_ignorelist(Module, XrefCheck)
                            end, SearchModules),

    [Result || Result <- XrefResults,
               not lists:member(parse_xref_result(Result), Ignores)].


display_xref_result(Type, XrefResult) ->
    { Source, SMFA, TMFA } = case XrefResult of
                                 {MFASource, MFATarget} ->
                                     {format_mfa_source(MFASource),
                                      format_mfa(MFASource),
                                      format_mfa(MFATarget)};
                                 MFATarget ->
                                     {format_mfa_source(MFATarget),
                                      format_mfa(MFATarget),
                                      undefined}
                             end,
    case Type of
        undefined_function_calls ->
            ?CONSOLE("~sWarning: ~s calls undefined function ~s (Xref)\n",
                     [Source, SMFA, TMFA]);
        undefined_functions ->
            ?CONSOLE("~sWarning: ~s is undefined function (Xref)\n",
                     [Source, SMFA]);
        locals_not_used ->
            ?CONSOLE("~sWarning: ~s is unused local function (Xref)\n",
                     [Source, SMFA]);
        exports_not_used ->
            ?CONSOLE("~sWarning: ~s is unused export (Xref)\n",
                     [Source, SMFA]);
        deprecated_function_calls ->
            ?CONSOLE("~sWarning: ~s calls deprecated function ~s (Xref)\n",
                     [Source, SMFA, TMFA]);
        deprecated_functions ->
            ?CONSOLE("~sWarning: ~s is deprecated function (Xref)\n",
                     [Source, SMFA]);
        Other ->
            ?CONSOLE("~sWarning: ~s - ~s xref check: ~s (Xref)\n",
                     [Source, SMFA, TMFA, Other])
    end.


format_mfa({M, F, A}) ->
    ?FMT("~s:~s/~w", [M, F, A]).


format_mfa_source(MFA) ->
    case find_mfa_source(MFA) of
        {module_not_found, function_not_found} -> "";
        {Source, function_not_found} -> ?FMT("~s: ", [Source]);
        {Source, Line} -> ?FMT("~s:~w: ", [Source, Line])
    end.

%%
%% Extract an element from a tuple, or undefined if N > tuple size
%%
safe_element(N, Tuple) ->
    case catch(element(N, Tuple)) of
        {'EXIT', {badarg, _}} ->
            undefined;
        Value ->
            Value
    end.


%%
%% Given a MFA, find the file and LOC where it's defined. Note that
%% xref doesn't work if there is no abstract_code, so we can avoid
%% being too paranoid here.
%%
find_mfa_source({M, F, A}) ->
    case code:get_object_code(M) of
        error -> {module_not_found, function_not_found};
        {M, Bin, _} -> find_function_source(M,F,A,Bin)
    end.


find_function_source(M, F, A, Bin) ->
    AbstractCode = beam_lib:chunks(Bin, [abstract_code]),
    {ok, {M, [{abstract_code, {raw_abstract_v1, Code}}]}} = AbstractCode,
    %% Extract the original source filename from the abstract code
    [{attribute, 1, file, {Source, _}} | _] = Code,
    %% Extract the line number for a given function def
    Fn = [E || E <- Code,
               safe_element(1, E) == function,
               safe_element(3, E) == F,
               safe_element(4, E) == A],
    case Fn of
        [{function, Line, F, _, _}] -> {Source, Line};
        %% do not crash if functions are exported, even though they
        %% are not in the source.
        %% parameterized modules add new/1 and instance/1 for example.
        [] -> {Source, function_not_found}
    end.