Add syntax in try/catch to retrieve the stacktrace directly

This commit adds a new syntax for retrieving the stacktrace
without calling erlang:get_stacktrace/0. That allow us to
deprecate erlang:get_stacktrace/0 and ultimately remove it.

The problem with erlang:get_stacktrace/0 is that it can keep huge
terms in a process for an indefinite time after an exception. The
stacktrace can be huge after a 'function_clause' exception or a failed
call to a BIF or operator, because the arguments for the call will be
included in the stacktrace. For example:

1> catch abs(lists:seq(1, 1000)).
{'EXIT',{badarg,[{erlang,abs,
                         [[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20|...]],
                         []},
                 {erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,674}]},
                 {erl_eval,expr,5,[{file,"erl_eval.erl"},{line,431}]},
                 {shell,exprs,7,[{file,"shell.erl"},{line,687}]},
                 {shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
                 {shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]}}
2> erlang:get_stacktrace().
[{erlang,abs,
         [[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,
           23,24|...]],
         []},
 {erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,674}]},
 {erl_eval,expr,5,[{file,"erl_eval.erl"},{line,431}]},
 {shell,exprs,7,[{file,"shell.erl"},{line,687}]},
 {shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
 {shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]
3>

We can extend the syntax for clauses in try/catch to optionally bind
the stacktrace to a variable.

Here is an example using the current syntax:

    try
      Expr
    catch C:E ->
      Stk = erlang:get_stacktrace(),
      .
      .
      .

In the new syntax, it would look like:

    try
      Expr
    catch
      C:E:Stk ->
       .
       .
       .

Only a variable (not a pattern) is allowed in the stacktrace position,
to discourage matching of the stacktrace. (Matching would also be
expensive, because the raw format of the stacktrace would have to be
converted to the cooked form before matching.)

Note that:

    try
      Expr
    catch E ->
      .
      .
      .

is a shorthand for:

    try
      Expr
    catch throw:E ->
      .
      .
      .

If the stacktrace is to be retrieved for a throw, the 'throw:'
prefix must be explicitly included:

    try
      Expr
    catch throw:E:Stk ->
      .
      .
      .

9 files changed, 173 insertions, 5 deletions

diff --git a/lib/compiler/src/beam_disasm.erl b/lib/compiler/src/beam_disasm.erl
index 8fd0b36d05..5858b14409 100644
--- a/lib/compiler/src/beam_disasm.erl
+++ b/lib/compiler/src/beam_disasm.erl
@@ -1165,6 +1165,13 @@ resolve_inst({get_map_elements,Args0},_,_,_) ->
     {get_map_elements,FLbl,Src,{list,List}};
 
 %%
+%% OTP 21.
+%%
+
+resolve_inst({build_stacktrace,[]},_,_,_) ->
+    build_stacktrace;
+
+%%
 %% Catches instructions that are not yet handled.
 %%
 resolve_inst(X,_,_,_) -> ?exit({resolve_inst,X}).
diff --git a/lib/compiler/src/beam_disasm.hrl b/lib/compiler/src/beam_disasm.hrl
index d968cd9587..8cc0bcf99b 100644
--- a/lib/compiler/src/beam_disasm.hrl
+++ b/lib/compiler/src/beam_disasm.hrl
@@ -26,7 +26,8 @@
 %%      IT SHOULD BE MOVED TO A FILE THAT DEFINES (AND EXPORTS)
 %%      PROPER TYPES FOR THE SET OF BEAM INSTRUCTIONS.
 %%
--type beam_instr() :: 'bs_init_writable' | 'fclearerror' | 'if_end'
+-type beam_instr() :: 'bs_init_writable' | 'build_stacktrace'
+                    | 'fclearerror' | 'if_end'
                     | 'remove_message' | 'return' | 'send' | 'timeout'
                     | tuple().  %% XXX: Very underspecified - FIX THIS
 
diff --git a/lib/compiler/src/beam_utils.erl b/lib/compiler/src/beam_utils.erl
index dd7ec4da96..1b2a2827cb 100644
--- a/lib/compiler/src/beam_utils.erl
+++ b/lib/compiler/src/beam_utils.erl
@@ -781,6 +781,8 @@ live_opt([{block,Bl0}|Is], Regs0, D, Acc) ->
     {Bl,Regs} = live_opt_block(reverse(Bl0), Regs0, D, [Live0]),
     Live = {'%live',live_regs(Regs),Regs},
     live_opt(Is, Regs, D, [{block,[Live|Bl]}|Acc]);
+live_opt([build_stacktrace=I|Is], _, D, Acc) ->
+    live_opt(Is, live_call(1), D, [I|Acc]);
 live_opt([{label,L}=I|Is], Regs, D0, Acc) ->
     D = gb_trees:insert(L, Regs, D0),
     live_opt(Is, Regs, D, [I|Acc]);
diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
index be8908dd6b..77f9fcebad 100644
--- a/lib/compiler/src/beam_validator.erl
+++ b/lib/compiler/src/beam_validator.erl
@@ -294,6 +294,8 @@ valfun_1({bs_context_to_binary,Ctx}, #vst{current=#st{x=Xs}}=Vst) ->
     end;
 valfun_1(bs_init_writable=I, Vst) ->
     call(I, 1, Vst);
+valfun_1(build_stacktrace=I, Vst) ->
+    call(I, 1, Vst);
 valfun_1({move,{y,_}=Src,{y,_}=Dst}, Vst) ->
     %% The stack trimming optimization may generate a move from an initialized
     %% but unassigned Y register to another Y register.
diff --git a/lib/compiler/src/genop.tab b/lib/compiler/src/genop.tab
index b5688de339..397e478e1e 100755
--- a/lib/compiler/src/genop.tab
+++ b/lib/compiler/src/genop.tab
@@ -545,3 +545,12 @@ BEAM_FORMAT_NUMBER=0
 ##      Test the arity of Reg and jumps to Lbl if it is not N.
 ##      Test the first element of the tuple and jumps to Lbl if it is not Atom.
 159: is_tagged_tuple/4
+
+# OTP 21
+
+## @spec build_stacktrace
+## @doc  Given the raw stacktrace in x(0), build a cooked stacktrace suitable
+##       for human consumption. Store it in x(0). Destroys all other registers.
+##       Do a garbage collection if necessary to allocate space on the heap
+##       for the result.
+160: build_stacktrace/0
diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl
index df880ff784..6da68f1f4e 100644
--- a/lib/compiler/src/sys_core_fold.erl
+++ b/lib/compiler/src/sys_core_fold.erl
@@ -415,6 +415,8 @@ expr(#c_call{module=M0,name=N0}=Call0, Ctxt, Sub) ->
 	no -> call(Call, M1, N1, Sub);
 	{yes,Seq} -> expr(Seq, Ctxt, Sub)
     end;
+expr(#c_primop{name=#c_literal{val=build_stacktrace}}, effect, _Sub) ->
+    void();
 expr(#c_primop{args=As0}=Prim, _, Sub) ->
     As1 = expr_list(As0, value, Sub),
     Prim#c_primop{args=As1};
diff --git a/lib/compiler/src/v3_codegen.erl b/lib/compiler/src/v3_codegen.erl
index 535c0679d8..9bcd6987bf 100644
--- a/lib/compiler/src/v3_codegen.erl
+++ b/lib/compiler/src/v3_codegen.erl
@@ -1656,6 +1656,11 @@ internal_cg(bs_init_writable=I, As, Rs, Le, Vdb, Bef, St) ->
     {Sis,Int} = cg_setup_call(As, Bef, Le#l.i, Vdb),
     Reg = load_vars(Rs, clear_regs(Int#sr.reg)),
     {Sis++[I],clear_dead(Int#sr{reg=Reg}, Le#l.i, Vdb),St};
+internal_cg(build_stacktrace=I, As, Rs, Le, Vdb, Bef, St) ->
+    %% This behaves like a function call.
+    {Sis,Int} = cg_setup_call(As, Bef, Le#l.i, Vdb),
+    Reg = load_vars(Rs, clear_regs(Int#sr.reg)),
+    {Sis++[I],clear_dead(Int#sr{reg=Reg}, Le#l.i, Vdb),St};
 internal_cg(raise, As, Rs, Le, Vdb, Bef, St) ->
     %% raise can be treated like a guard BIF.
     bif_cg(raise, As, Rs, Le, Vdb, Bef, St).
diff --git a/lib/compiler/src/v3_core.erl b/lib/compiler/src/v3_core.erl
index 20cb3343fb..cc8ea475d2 100644
--- a/lib/compiler/src/v3_core.erl
+++ b/lib/compiler/src/v3_core.erl
@@ -920,8 +920,9 @@ try_exception(Ecs0, St0) ->
     %% Note that Tag is not needed for rethrow - it is already in Info.
     {Evs,St1} = new_vars(3, St0), % Tag, Value, Info
     {Ecs1,Ceps,St2} = clauses(Ecs0, St1),
+    Ecs2 = try_build_stacktrace(Ecs1, hd(Evs)),
     [_,Value,Info] = Evs,
-    LA = case Ecs1 of
+    LA = case Ecs2 of
 	     [] -> [];
 	     [C|_] -> get_lineno_anno(C)
 	 end,
@@ -930,7 +931,7 @@ try_exception(Ecs0, St0) ->
 		  body=[#iprimop{anno=#a{},       %Must have an #a{}
 				 name=#c_literal{val=raise},
 				 args=[Info,Value]}]},
-    Hs = [#icase{anno=#a{anno=LA},args=[c_tuple(Evs)],clauses=Ecs1,fc=Ec}],
+    Hs = [#icase{anno=#a{anno=LA},args=[c_tuple(Evs)],clauses=Ecs2,fc=Ec}],
     {Evs,Ceps++Hs,St2}.
 
 try_after(As, St0) ->
@@ -946,6 +947,25 @@ try_after(As, St0) ->
     Hs = [#icase{anno=#a{},args=[c_tuple(Evs)],clauses=[],fc=Ec}],
     {Evs,Hs,St1}.
 
+try_build_stacktrace([#iclause{pats=Ps0,body=B0}=C0|Cs], RawStk) ->
+    [#c_tuple{es=[Class,Exc,Stk]}=Tup] = Ps0,
+    case Stk of
+        #c_var{name='_'} ->
+            %% Stacktrace variable is not used. Nothing to do.
+            [C0|try_build_stacktrace(Cs, RawStk)];
+        _ ->
+            %% Add code to build the stacktrace.
+            Ps = [Tup#c_tuple{es=[Class,Exc,RawStk]}],
+            Call = #iprimop{anno=#a{},
+                            name=#c_literal{val=build_stacktrace},
+                            args=[RawStk]},
+            Iset = #iset{var=Stk,arg=Call},
+            B = [Iset|B0],
+            C = C0#iclause{pats=Ps,body=B},
+            [C|try_build_stacktrace(Cs, RawStk)]
+    end;
+try_build_stacktrace([], _) -> [].
+
 %% expr_bin([ArgExpr], St) -> {[Arg],[PreExpr],St}.
 %%  Flatten the arguments of a bin. Do this straight left to right!
 %%  Note that ibinary needs to have its annotation wrapped in a #a{}
diff --git a/lib/compiler/test/trycatch_SUITE.erl b/lib/compiler/test/trycatch_SUITE.erl
index 42dbf7d5f0..8cf7928cc4 100644
--- a/lib/compiler/test/trycatch_SUITE.erl
+++ b/lib/compiler/test/trycatch_SUITE.erl
@@ -26,7 +26,8 @@
 	 nested_of/1,nested_catch/1,nested_after/1,
 	 nested_horrid/1,last_call_optimization/1,bool/1,
 	 plain_catch_coverage/1,andalso_orelse/1,get_in_try/1,
-	 hockey/1,handle_info/1,catch_in_catch/1,grab_bag/1]).
+	 hockey/1,handle_info/1,catch_in_catch/1,grab_bag/1,
+         stacktrace/1,nested_stacktrace/1]).
 
 -include_lib("common_test/include/ct.hrl").
 
@@ -42,7 +43,8 @@ groups() ->
        after_oops,eclectic,rethrow,nested_of,nested_catch,
        nested_after,nested_horrid,last_call_optimization,
        bool,plain_catch_coverage,andalso_orelse,get_in_try,
-       hockey,handle_info,catch_in_catch,grab_bag]}].
+       hockey,handle_info,catch_in_catch,grab_bag,
+       stacktrace,nested_stacktrace]}].
 
 
 init_per_suite(Config) ->
@@ -1039,5 +1041,123 @@ grab_bag(_Config) ->
 
     ok.
 
+stacktrace(_Config) ->
+    V = [make_ref()|self()],
+    case ?MODULE:module_info(native) of
+        false ->
+            {value2,{caught1,badarg,[{erlang,abs,[V],_}|_]}} =
+                stacktrace_1({'abs',V}, error, {value,V}),
+            {caught2,{error,badarith},[{erlang,'+',[0,a],_},
+                                       {?MODULE,my_add,2,_}|_]} =
+                stacktrace_1({'div',{1,0}}, error, {'add',{0,a}});
+        true ->
+            {value2,{caught1,badarg,[{?MODULE,my_abs,1,_}|_]}} =
+                stacktrace_1({'abs',V}, error, {value,V}),
+            {caught2,{error,badarith},[{?MODULE,my_add,2,_}|_]} =
+                stacktrace_1({'div',{1,0}}, error, {'add',{0,a}})
+    end,
+    {caught2,{error,{try_clause,V}},[{?MODULE,stacktrace_1,3,_}|_]} =
+        stacktrace_1({value,V}, error, {value,V}),
+    {caught2,{throw,V},[{?MODULE,foo,1,_}|_]} =
+        stacktrace_1({value,V}, error, {throw,V}),
+
+    try
+        stacktrace_2()
+    catch
+        error:{badmatch,_}:Stk2 ->
+            [{?MODULE,stacktrace_2,0,_},
+             {?MODULE,stacktrace,1,_}|_] = Stk2,
+            Stk2 = erlang:get_stacktrace(),
+            ok
+    end,
+
+    try
+        stacktrace_3(a, b)
+    catch
+        error:function_clause:Stk3 ->
+            Stk3 = erlang:get_stacktrace(),
+            case lists:module_info(native) of
+                false ->
+                    [{lists,prefix,[a,b],_}|_] = Stk3;
+                true ->
+                    [{lists,prefix,2,_}|_] = Stk3
+            end
+    end,
+
+    try
+        throw(x)
+    catch
+        throw:x:IntentionallyUnused ->
+            ok
+    end.
+
+stacktrace_1(X, C1, Y) ->
+    try try foo(X) of
+            C1 -> value1
+        catch
+            C1:D1:Stk1 ->
+                Stk1 = erlang:get_stacktrace(),
+                {caught1,D1,Stk1}
+        after
+            foo(Y)
+        end of
+        V2 -> {value2,V2}
+    catch
+        C2:D2:Stk2 -> {caught2,{C2,D2},Stk2=erlang:get_stacktrace()}
+    end.
+
+stacktrace_2() ->
+    ok = erlang:process_info(self(), current_function),
+    ok.
+
+stacktrace_3(A, B) ->
+    {ok,lists:prefix(A, B)}.
+
+nested_stacktrace(_Config) ->
+    V = [{make_ref()}|[self()]],
+    value1 = nested_stacktrace_1({{value,{V,x1}},void,{V,x1}},
+                                 {void,void,void}),
+    case ?MODULE:module_info(native) of
+        false ->
+            {caught1,
+             [{erlang,'+',[V,x1],_},{?MODULE,my_add,2,_}|_],
+             value2} =
+                nested_stacktrace_1({{'add',{V,x1}},error,badarith},
+                                    {{value,{V,x2}},void,{V,x2}}),
+            {caught1,
+             [{erlang,'+',[V,x1],_},{?MODULE,my_add,2,_}|_],
+             {caught2,[{erlang,abs,[V],_}|_]}} =
+                nested_stacktrace_1({{'add',{V,x1}},error,badarith},
+                                    {{'abs',V},error,badarg});
+        true ->
+            {caught1,
+             [{?MODULE,my_add,2,_}|_],
+             value2} =
+                nested_stacktrace_1({{'add',{V,x1}},error,badarith},
+                                    {{value,{V,x2}},void,{V,x2}}),
+            {caught1,
+             [{?MODULE,my_add,2,_}|_],
+             {caught2,[{?MODULE,my_abs,1,_}|_]}} =
+                nested_stacktrace_1({{'add',{V,x1}},error,badarith},
+                                    {{'abs',V},error,badarg})
+    end,
+    ok.
+
+nested_stacktrace_1({X1,C1,V1}, {X2,C2,V2}) ->
+    try foo(X1) of
+        V1 -> value1
+    catch
+        C1:V1:S1 ->
+            S1 = erlang:get_stacktrace(),
+            T2 = try foo(X2) of
+                     V2 -> value2
+                 catch
+                     C2:V2:S2 ->
+                         S2 = erlang:get_stacktrace(),
+                         {caught2,S2}
+                 end,
+            {caught1,S1,T2}
+    end.
+
 
 id(I) -> I.