Eliminate confusing `case_clause` exception

Consider this module:

    -module(bug).
    -export([foo/0]).

    foo() ->
        fun(a) -> ok end(b).

The call to the fun will always fail, which will be noted by
the compiler:

    1> c(bug).
    bug.erl:5:5: Warning: no clause will ever match
    %    5|     fun(a) -> ok end(b).
    %     |     ^

    {ok,bug}

What is unexpected is that the exception that is raised is not
a `function_clause` exception:

    2> bug:foo().
    ** exception error: no case clause matching {b}
         in function  bug:foo/0 (bug.erl, line 5)

This confusing `case_clause` exception started to appear in OTP 24
because of 72675baaa9fd30 (#4545) that inlines funs that are
immediately used.

Before OTP 24, when the fun was not inlined, the exception would be:

    2> bug:foo().
    ** exception error: no function clause matching bug:'-foo/0-fun-0-'(b) (bug.erl, line 5)

The reason that `function_clause` exceptions are rewritten to
`case_clause` exceptions in inlined code is to avoid the even more
confusing and misleading exception:

    2> bug:foo().
    ** exception error: no function clause matching bug:foo(b) (bug.erl, line 5)

This is confusing because it seems that `foo/0` was called with one argument.

To reduce the confusion, this commmit ensures that `function_clause` exceptions in
inlined code remains `function_clause` exceptions, but with a generated name that
makes it clear that the `function_clause` exception occurred in a fun:

    2> bug:foo().
    ** exception error: no function clause matching bug:'-foo/0-inlined-0-'(b) (bug.erl, line 5)

Fixes #5513

9 files changed, 165 insertions, 60 deletions

diff --git a/lib/compiler/src/beam_kernel_to_ssa.erl b/lib/compiler/src/beam_kernel_to_ssa.erl
index c2e22f4b6d..7722078206 100644
--- a/lib/compiler/src/beam_kernel_to_ssa.erl
+++ b/lib/compiler/src/beam_kernel_to_ssa.erl
@@ -25,7 +25,7 @@
 -export([module/2]).
 
 -import(lists, [all/2,append/1,flatmap/2,foldl/3,
-                keysort/2,mapfoldl/3,member/2,
+                keyfind/3,keysort/2,mapfoldl/3,member/2,
                 reverse/1,sort/1]).
 
 -include("v3_kernel.hrl").
@@ -672,7 +672,7 @@ call_cg(Func, As, [#k_var{name=R}|MoreRs]=Rs, Le, St0) ->
             %% Ordinary function call in a function body.
             Args = ssa_args([Func|As], St0),
             {Ret,St1} = new_ssa_var(R, St0),
-            Call = #b_set{anno=line_anno(Le),op=call,dst=Ret,args=Args},
+            Call = #b_set{anno=call_anno(Le),op=call,dst=Ret,args=Args},
 
             %% If this is a call to erlang:error(), MoreRs could be a
             %% nonempty list of variables that each need a value.
@@ -685,9 +685,16 @@ call_cg(Func, As, [#k_var{name=R}|MoreRs]=Rs, Le, St0) ->
 enter_cg(Func, As0, Le, St0) ->
     As = ssa_args([Func|As0], St0),
     {Ret,St} = new_ssa_var('@ssa_ret', St0),
-    Call = #b_set{anno=line_anno(Le),op=call,dst=Ret,args=As},
+    Call = #b_set{anno=call_anno(Le),op=call,dst=Ret,args=As},
     {[Call,#b_ret{arg=Ret}],St}.
 
+call_anno(Le) ->
+    Anno = line_anno(Le),
+    case keyfind(inlined, 1, Le) of
+        false -> Anno;
+        {inlined,NameArity} -> Anno#{inlined => NameArity}
+    end.
+
 %% bif_cg(#k_bif{}, Le,State) -> {[Ainstr],State}.
 %%  Generate code for a guard BIF or primop.
 
diff --git a/lib/compiler/src/beam_ssa_pre_codegen.erl b/lib/compiler/src/beam_ssa_pre_codegen.erl
index 3567fb4210..f5ad81f760 100644
--- a/lib/compiler/src/beam_ssa_pre_codegen.erl
+++ b/lib/compiler/src/beam_ssa_pre_codegen.erl
@@ -73,14 +73,16 @@
 
 -import(lists, [all/2,any/2,append/1,duplicate/2,
                 foldl/3,last/1,member/2,partition/2,
-                reverse/1,reverse/2,sort/1,splitwith/2,zip/2]).
+                reverse/1,reverse/2,seq/2,sort/1,
+                splitwith/2,usort/1,zip/2]).
 
 -spec module(beam_ssa:b_module(), [compile:option()]) ->
                     {'ok',beam_ssa:b_module()}.
 
 module(#b_module{body=Fs0}=Module, Opts) ->
     Ps = passes(Opts),
-    Fs = functions(Fs0, Ps),
+    Fs1 = functions(Fs0, Ps),
+    Fs = fc_stubs(Fs1, Module),
     {ok,Module#b_module{body=Fs}}.
 
 functions([F|Fs], Ps) ->
@@ -835,19 +837,21 @@ match_fail_instrs_1([{L,#b_blk{is=Is0}=Blk}|Bs], Arity, Blocks0) ->
 match_fail_instrs_1([], _Arity, Blocks) -> Blocks.
 
 match_fail_instrs_blk([#b_set{op=put_tuple,dst=Dst,
-                              args=[#b_literal{val=Tag},Val]},
+                              args=[#b_literal{val=Tag}|Values]},
                        #b_set{op=call,
                               args=[#b_remote{mod=#b_literal{val=erlang},
                                               name=#b_literal{val=error}},
                                     Dst]}=Call|Is],
                       _Arity, Acc) ->
-    match_fail_instr(Call, Tag, Val, Is, Acc);
+    match_fail_instr(Call, Tag, Values, Is, Acc);
 match_fail_instrs_blk([#b_set{op=call,
                               args=[#b_remote{mod=#b_literal{val=erlang},
                                               name=#b_literal{val=error}},
-                                    #b_literal{val={Tag,Val}}]}=Call|Is],
-                      _Arity, Acc) ->
-    match_fail_instr(Call, Tag, #b_literal{val=Val}, Is, Acc);
+                                    #b_literal{val=Tuple}]}=Call|Is],
+                      _Arity, Acc) when tuple_size(Tuple) >= 1 ->
+    [Tag|Values0] = tuple_to_list(Tuple),
+    Values = [#b_literal{val=V} || V <- Values0],
+    match_fail_instr(Call, Tag, Values, Is, Acc);
 match_fail_instrs_blk([#b_set{op=call,
                               args=[#b_remote{mod=#b_literal{val=erlang},
                                               name=#b_literal{val=error}},
@@ -860,34 +864,29 @@ match_fail_instrs_blk([#b_set{op=call,anno=Anno,
                                               name=#b_literal{val=error}},
                                     #b_literal{val=function_clause},
                                     Stk]}=Call],
-                      {Arity,Location}, Acc) ->
-    case match_fail_stk(Stk, Acc, [], []) of
-        {[_|_]=Vars,Is} when length(Vars) =:= Arity ->
-            case maps:get(location, Anno, none) of
-                Location ->
-                    I = Call#b_set{op=match_fail,
-                                   args=[#b_literal{val=function_clause}|Vars]},
-                    Is ++ [I];
-                _ ->
-                    %% erlang:error/2 has a different location than the
-                    %% func_info instruction at the beginning of the function
-                    %% (probably because of inlining). Keep the original call.
-                    reverse(Acc, [Call])
-            end;
-        _ ->
-            %% Either the stacktrace could not be picked apart (for example,
-            %% if the call to erlang:error/2 was handwritten) or the number
-            %% of arguments in the stacktrace was different from the arity
-            %% of the host function (because it is the implementation of a
-            %% fun). Keep the original call.
-            reverse(Acc, [Call])
-    end;
+                      Arity, Acc) ->
+    match_fail_fc(Anno, Call, Stk, Arity, Acc);
 match_fail_instrs_blk([I|Is], Arity, Acc) ->
     match_fail_instrs_blk(Is, Arity, [I|Acc]);
 match_fail_instrs_blk(_, _, _) ->
     none.
 
-match_fail_instr(Call, Tag, Val, Is, Acc) ->
+match_fail_instr(Call, function_clause, Values, Is, Acc) ->
+    case beam_ssa:get_anno(inlined, Call, none) of
+        none ->
+            %% If there is no `inlined` annotation, it implies that
+            %% the call to erlang:error/1 was handwritten.
+            none;
+        {Name,Arity} ->
+            %% A `function_clause` in inlined code. Convert it to
+            %% a call to a stub function that will raise a proper
+            %% `function_clause` exception. (The stub function will
+            %% be created later by fc_stubs/2.)
+            Target = #b_local{name=#b_literal{val=Name},arity=Arity},
+            I = Call#b_set{args=[Target|Values]},
+            reverse(Acc, [I|Is])
+    end;
+match_fail_instr(Call, Tag, [Val], Is, Acc) ->
     Op = case Tag of
              badmatch -> Tag;
              case_clause -> case_end;
@@ -900,19 +899,84 @@ match_fail_instr(Call, Tag, Val, Is, Acc) ->
         _ ->
             I = Call#b_set{op=match_fail,args=[#b_literal{val=Op},Val]},
             reverse(Acc, [I|Is])
+    end;
+match_fail_instr(_, _, _, _, _) -> none.
+
+match_fail_fc(Anno, Call, Stk, {Arity,Location}, Acc) ->
+    case match_fail_stk(Stk, Acc, [], []) of
+        {[_|_]=Vars,Is} when length(Vars) =:= Arity ->
+            case maps:get(location, Anno, none) of
+                Location ->
+                    I = Call#b_set{op=match_fail,
+                                   args=[#b_literal{val=function_clause}|Vars]},
+                    Is ++ [I];
+                _ ->
+                    %% erlang:error/2 has a different location than
+                    %% the func_info instruction at the beginning of
+                    %% the function (probably because of
+                    %% inlining). Keep the original call.
+                    reverse(Acc, [Call])
+            end;
+        _ ->
+            %% Either the stacktrace could not be picked apart (for
+            %% example, if the call to erlang:error/2 was handwritten)
+            %% or the number of arguments in the stacktrace was
+            %% different from the arity of the host function (because
+            %% it is the implementation of a fun). Keep the original
+            %% call.
+            reverse(Acc, [Call])
     end.
 
 match_fail_stk(#b_var{}=V, [#b_set{op=put_list,dst=V,args=[H,T]}|Is], IAcc, VAcc) ->
     match_fail_stk(T, Is, IAcc, [H|VAcc]);
 match_fail_stk(#b_literal{val=[H|T]}, Is, IAcc, VAcc) ->
     match_fail_stk(#b_literal{val=T}, Is, IAcc, [#b_literal{val=H}|VAcc]);
-match_fail_stk(#b_literal{val=[]}, [], IAcc, VAcc) ->
-    {reverse(VAcc),IAcc};
+match_fail_stk(#b_literal{val=[]}, Is, IAcc, VAcc) ->
+    {reverse(VAcc),reverse(Is, IAcc)};
 match_fail_stk(T, [#b_set{op=Op}=I|Is], IAcc, VAcc)
   when Op =:= bs_get_tail; Op =:= bs_set_position ->
     match_fail_stk(T, Is, [I|IAcc], VAcc);
 match_fail_stk(_, _, _, _) -> none.
 
+%% Create stubs for `function_clause` exceptions generated by
+%% inlined code.
+fc_stubs(Fs, #b_module{name=Mod}) ->
+    Stubs0 = usort(find_fc_calls(Fs, [])),
+    Stubs = [begin
+                 Seq = seq(0, Arity-1),
+                 Args = [#b_var{name=V} || V <- Seq],
+                 XRegs = [{x,V} || V <- Seq],
+                 Ret = #b_var{name='@ssa_ret'},
+                 Regs = maps:from_list([{Ret,{x,0}}|zip(Args, XRegs)]),
+                 Anno = #{func_info => {Mod,Name,Arity},
+                          location => Location,
+                          parameter_info => #{},
+                          registers => Regs},
+                 Fc = #b_set{op=match_fail,dst=Ret,
+                             args=[#b_literal{val=function_clause}|Args]},
+                 Blk = #b_blk{is=[Fc],last=#b_ret{arg=Ret}},
+                 #b_function{anno=Anno,args=Args,
+                             bs=#{0 => Blk},
+                             cnt=1}
+             end || {{Name,Arity},Location} <- Stubs0],
+    Fs ++ Stubs.
+
+find_fc_calls([#b_function{bs=Blocks}|Fs], Acc0) ->
+    F = fun(#b_set{anno=Anno,op=call}, A) ->
+                case Anno of
+                    #{inlined := FA} ->
+                        [{FA,maps:get(location, Anno, [])}|A];
+                    #{} ->
+                        A
+                end;
+           (_, A) ->
+                A
+        end,
+    Acc = beam_ssa:fold_instrs(F, maps:keys(Blocks), Acc0, Blocks),
+    find_fc_calls(Fs, Acc);
+find_fc_calls([], Acc) -> Acc.
+
+
 %%%
 %%% Introduce the set_tuple_element instructions to make
 %%% multiple-field record updates faster.
diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
index 125c01c6a6..adbddc7059 100644
--- a/lib/compiler/src/beam_validator.erl
+++ b/lib/compiler/src/beam_validator.erl
@@ -245,7 +245,8 @@ build_function_table([{function,Name,Arity,Entry,Code0}|Fs], Acc) ->
         [{label,Entry} | Is] ->
             Info = #{ name => Name,
                       arity => Arity,
-                      parameter_info => find_parameter_info(Is, #{}) },
+                      parameter_info => find_parameter_info(Is, #{}),
+                      always_fails => always_fails(Is) },
             build_function_table(Fs, Acc#{ Entry => Info });
         _ ->
             %% Something is seriously wrong. Ignore it for now.
@@ -262,6 +263,9 @@ find_parameter_info([{'%', _} | Is], Acc) ->
 find_parameter_info(_, Acc) ->
     Acc.
 
+always_fails([{jump,_}|_]) -> true;
+always_fails(_) -> false.
+
 validate_1(Is, MFA0, Entry, Level, Ft) ->
     {Offset, MFA, Header, Body} = extract_header(Is, MFA0, Entry, 1, []),
 
@@ -3078,6 +3082,13 @@ will_call_succeed(bs_init_writable, _Vst) ->
     yes;
 will_call_succeed(raw_raise, _Vst) ->
     no;
+will_call_succeed({f,Lbl}, #vst{ft=Ft}) ->
+    case Ft of
+        #{Lbl := #{always_fails := true}} ->
+            no;
+        #{} ->
+            maybe
+    end;
 will_call_succeed(_Call, _Vst) ->
     maybe.
 
diff --git a/lib/compiler/src/v3_core.erl b/lib/compiler/src/v3_core.erl
index 6bf87e131c..8e89c88318 100644
--- a/lib/compiler/src/v3_core.erl
+++ b/lib/compiler/src/v3_core.erl
@@ -264,7 +264,7 @@ body(Cs0, Name, Arity, St0) ->
     Args = reverse(Args0),                      %Nicer order
     {Cs1,St2} = clauses(Cs0, St1),
     {Ps,St3} = new_vars(Arity, St2),    %Need new variables here
-    Fc = function_clause(Ps, Anno),
+    Fc = function_clause(Ps, FunAnno),
     {#ifun{anno=#a{anno=FunAnno},id=[],vars=Args,clauses=Cs1,fc=Fc},St3}.
 
 %% clause(Clause, State) -> {Cclause,State}.
diff --git a/lib/compiler/src/v3_kernel.erl b/lib/compiler/src/v3_kernel.erl
index aa3fc033eb..aa8a906ca7 100644
--- a/lib/compiler/src/v3_kernel.erl
+++ b/lib/compiler/src/v3_kernel.erl
@@ -405,36 +405,51 @@ letrec_goto([{#c_var{name={Label,0}},Cfail}], Cb, Sub0,
 %%  erlang:error/2.
 
 translate_match_fail(Arg, Sub, Anno, St0) ->
-    Cargs = case {cerl:data_type(Arg),cerl:data_es(Arg)} of
-                {tuple,[#c_literal{val=function_clause}|As]} ->
-                    translate_fc_args(As, Sub, St0);
-                {_,_} ->
-                    [Arg]
-            end,
-    {Kargs,Ap,St} = atomic_list(Cargs, Sub, St0),
+    {Cargs,ExtraAnno,St1} =
+        case {cerl:data_type(Arg),cerl:data_es(Arg)} of
+            {tuple,[#c_literal{val=function_clause}|As]} ->
+                translate_fc_args(As, Sub, Anno, St0);
+            {_,_} ->
+                {[Arg],[],St0}
+        end,
+    {Kargs,Ap,St} = atomic_list(Cargs, Sub, St1),
     Ar = length(Cargs),
-    Call = #k_call{anno=Anno,
+    Call = #k_call{anno=ExtraAnno++Anno,
                    op=#k_remote{mod=#k_literal{val=erlang},
                                 name=#k_literal{val=error},
                                 arity=Ar},args=Kargs},
     {Call,Ap,St}.
 
-translate_fc_args(As, Sub, #kern{fargs=Fargs}) ->
+translate_fc_args(As, Sub, Anno, #kern{fargs=Fargs}=St0) ->
     case same_args(As, Fargs, Sub) of
         true ->
             %% The arguments for the `function_clause` exception are
             %% the arguments for the current function in the correct
             %% order.
-            [#c_literal{val=function_clause},cerl:make_list(As)];
+            {[#c_literal{val=function_clause},cerl:make_list(As)],
+             [],
+             St0};
         false ->
             %% The arguments in the `function_clause` exception don't
-            %% match the arguments for the current function because
-            %% of inlining. Keeping the `function_clause`
-            %% exception reason would be confusing. Rewrite it to
-            %% a `case_clause` exception with the arguments in a
-            %% tuple.
-	    [cerl:c_tuple([#c_literal{val=case_clause},
-                           cerl:c_tuple(As)])]
+            %% match the arguments for the current function because of
+            %% inlining.
+            Args = [cerl:c_tuple([#c_literal{val=function_clause}|As])],
+            case keyfind(function, 1, Anno) of
+                false ->
+                    %% This is probably a fun that has been inlined
+                    %% by sys_core_fold.
+                    {Name,St1} = new_fun_name("inlined", St0),
+                    {Args,
+                     [{inlined,{Name,length(As)}}],
+                     St1};
+                {_,{Name0,Arity}} ->
+                    %% This is function that has been inlined.
+                    Name1 = ["-inlined-",Name0,"/",Arity,"-"],
+                    Name = list_to_atom(lists:concat(Name1)),
+                    {Args,
+                     [{inlined,{Name,Arity}}],
+                     St0}
+            end
     end.
 
 same_args([#c_var{name=Cv}|Vs], [#k_var{name=Kv}|As], Sub) ->
diff --git a/lib/compiler/test/beam_except_SUITE.erl b/lib/compiler/test/beam_except_SUITE.erl
index 95e5989081..2bc805be71 100644
--- a/lib/compiler/test/beam_except_SUITE.erl
+++ b/lib/compiler/test/beam_except_SUITE.erl
@@ -135,14 +135,18 @@ coverage(_) ->
     {'EXIT',{function_clause,[{?MODULE,foobar,[[fail],1,2],
                                [{file,"fake.erl"},{line,16}]}|_]}} =
         (catch foobar([fail], 1, 2)),
+
     {'EXIT',{function_clause,[{?MODULE,fake_function_clause1,[{a,b},42.0],_}|_]}} =
         (catch fake_function_clause1({a,b})),
 
     {'EXIT',{function_clause,[{?MODULE,fake_function_clause2,[42|bad_tl],_}|_]}} =
         (catch fake_function_clause2(42, bad_tl)),
+
     {'EXIT',{function_clause,[{?MODULE,fake_function_clause3,[x,y],_}|_]}} =
         (catch fake_function_clause3(42, id([x,y]))),
 
+    {'EXIT',{{function_clause,a,b,c}, _}} = catch fake_function_clause4(),
+
     {'EXIT',{{badmatch,0.0},_}} = (catch coverage_1(id(42))),
     {'EXIT',{badarith,_}} = (catch coverage_1(id(a))),
 
@@ -153,9 +157,13 @@ coverage_1(X) ->
     true = 0 / X.
 
 fake_function_clause1(A) -> error(function_clause, [A,42.0]).
+
 fake_function_clause2(A, Tl) -> error(function_clause, [A|Tl]).
+
 fake_function_clause3(_, Stk) -> error(function_clause, Stk).
 
+fake_function_clause4() -> error({function_clause,a,b,c}).
+
 binary_construction_allocation(_Config) ->
     ok = do_binary_construction_allocation("PUT"),
     ok.
diff --git a/lib/compiler/test/bs_match_SUITE.erl b/lib/compiler/test/bs_match_SUITE.erl
index f7542be568..96ae549b28 100644
--- a/lib/compiler/test/bs_match_SUITE.erl
+++ b/lib/compiler/test/bs_match_SUITE.erl
@@ -1468,10 +1468,11 @@ haystack_2(Haystack) ->
 fc({'EXIT',{function_clause,_}}) -> ok;
 fc({'EXIT',{{case_clause,_},_}}) when ?MODULE =:= bs_match_inline_SUITE -> ok.
 
-fc(Name, Args, {'EXIT',{function_clause,[{?MODULE,Name,Args,_}|_]}}) -> ok;
-fc(_, Args, {'EXIT',{{case_clause,ActualArgs},_}})
+fc(Name, Args, {'EXIT',{function_clause,[{?MODULE,Name,Args,_}|_]}}) ->
+    ok;
+fc(Name, Args, {'EXIT',{function_clause,[{?MODULE,_,Args,_}|_]}})
   when ?MODULE =:= bs_match_inline_SUITE ->
-    Args = tuple_to_list(ActualArgs).
+    ok.
 
 %% Cover the clause handling bs_context to binary in
 %% beam_block:initialized_regs/2.
diff --git a/lib/compiler/test/guard_SUITE.erl b/lib/compiler/test/guard_SUITE.erl
index 6699d82262..6a42453654 100644
--- a/lib/compiler/test/guard_SUITE.erl
+++ b/lib/compiler/test/guard_SUITE.erl
@@ -3070,5 +3070,4 @@ check(F, Result) ->
 	    ct:fail(check_failed)
     end.
 
-fc({'EXIT',{function_clause,_}}) -> ok;
-fc({'EXIT',{{case_clause,_},_}}) when ?MODULE =:= guard_inline_SUITE -> ok.
+fc({'EXIT',{function_clause,_}}) -> ok.
diff --git a/lib/compiler/test/inline_SUITE.erl b/lib/compiler/test/inline_SUITE.erl
index 7482f53ed4..b2778bebcd 100644
--- a/lib/compiler/test/inline_SUITE.erl
+++ b/lib/compiler/test/inline_SUITE.erl
@@ -332,7 +332,7 @@ badarg(Reply, _A) ->
     Reply.
 
 otp_7223(Config) when is_list(Config) ->
-    {'EXIT', {{case_clause,{1}},_}} = (catch otp_7223_1(1)),
+    {'EXIT', {function_clause, [{?MODULE,_,[1],_}|_]}} = (catch otp_7223_1(1)),
     ok.
 
 -compile({inline,[{otp_7223_1,1}]}).