From b5d657f176a440176eb073f749baadb7c45e19e4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 19 Apr 2018 11:24:38 +0200
Subject: Make stacktraces consistent when backtrace_depth is 0

It is allowed to set the backtrace depth to 0, but when
an exception is catched the stacktrace will still contain
one element:

    1> erlang:system_flag(backtrace_depth, 0).
    8
    2> catch error(badarg).
    {'EXIT',{badarg,[{shell,apply_fun,3,
                        [{file,"shell.erl"},{line,908}]}]}}

However, when an exception is raised using `erlang:raise/3`, there
will be no elements in the stacktrace:

    3> catch erlang:raise(error, badarg, [{fake,name,[arg],[]}]).
    {'EXIT',{badarg,[]}}

Since the `error_handler` module uses `erlang:raise/3` to
raise an exception when an undefined function is called,
there will not be any stacktrace when calling an undefined
function:

    4> catch undef_module:undef_name(some_argument).
    {'EXIT',{undef,[]}}

Fix this inconsistency by changing `erlang:raise/3` so that
it always includes one element in the stacktrace:

    3> catch erlang:raise(error, badarg, [{fake,name,[arg],[]}]).
    {'EXIT',{badarg,[{fake,name,[arg],[]}]}}
    4> catch undef_module:undef_name(some_argument).
    {'EXIT',{undef,[{undef_module,undef_name,[some_argument],[]}]}}
---
 erts/emulator/beam/bif.c               |  7 +++++
 erts/emulator/test/exception_SUITE.erl | 56 ++++++++++++++++++++++++++++++++--
 2 files changed, 61 insertions(+), 2 deletions(-)

(limited to 'erts')

diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c
index 017faffa48..79244b8544 100644
--- a/erts/emulator/beam/bif.c
+++ b/erts/emulator/beam/bif.c
@@ -1150,6 +1150,13 @@ BIF_RETTYPE raise_3(BIF_ALIST_3)
     /* Create stacktrace and store */
     if (erts_backtrace_depth < depth) {
 	depth = erts_backtrace_depth;
+        if (depth == 0) {
+            /*
+             * For consistency with stacktraces generated
+             * automatically, always include one element.
+             */
+            depth = 1;
+        }
 	must_copy = 1;
     }
     if (must_copy) {
diff --git a/erts/emulator/test/exception_SUITE.erl b/erts/emulator/test/exception_SUITE.erl
index da0292f385..60d14ce841 100644
--- a/erts/emulator/test/exception_SUITE.erl
+++ b/erts/emulator/test/exception_SUITE.erl
@@ -23,7 +23,8 @@
 -export([all/0, suite/0,
          badmatch/1, pending_errors/1, nil_arith/1, top_of_stacktrace/1,
          stacktrace/1, nested_stacktrace/1, raise/1, gunilla/1, per/1,
-         exception_with_heap_frag/1, line_numbers/1]).
+         exception_with_heap_frag/1, backtrace_depth/1,
+         line_numbers/1]).
 
 -export([bad_guy/2]).
 -export([crash/1]).
@@ -42,7 +43,7 @@ suite() ->
 all() -> 
     [badmatch, pending_errors, nil_arith, top_of_stacktrace,
      stacktrace, nested_stacktrace, raise, gunilla, per,
-     exception_with_heap_frag, line_numbers].
+     exception_with_heap_frag, backtrace_depth, line_numbers].
 
 -define(try_match(E),
         catch ?MODULE:bar(),
@@ -572,6 +573,57 @@ do_exception_with_heap_frag(Bin, [Sz|Sizes]) ->
     do_exception_with_heap_frag(Bin, Sizes);
 do_exception_with_heap_frag(_, []) -> ok.
 
+backtrace_depth(Config) when is_list(Config) ->
+    _ = [do_backtrace_depth(D) || D <- lists:seq(0, 8)],
+    ok.
+
+do_backtrace_depth(D) ->
+    Old = erlang:system_flag(backtrace_depth, D),
+    try
+        Expected = max(1, D),
+        do_backtrace_depth_1(Expected)
+    after
+        _ = erlang:system_flag(backtrace_depth, Old)
+    end.
+
+do_backtrace_depth_1(D) ->
+    Exit = fun() ->
+                   error(reason)
+           end,
+    HandCrafted = fun() ->
+                          {'EXIT',{_,Stk0}} = (catch error(get_stacktrace)),
+                          %% Fool the compiler to force a hand-crafted
+                          %% stacktrace.
+                          Stk = [hd(Stk0)|tl(Stk0)],
+                          erlang:raise(error, reason, Stk)
+                  end,
+    PassedOn = fun() ->
+                       try error(get_stacktrace)
+                       catch error:_:Stk ->
+                               %% Just pass on the given stacktrace.
+                               erlang:raise(error, reason, Stk)
+                       end
+               end,
+    do_backtrace_depth_2(D, Exit),
+    do_backtrace_depth_2(D, HandCrafted),
+    do_backtrace_depth_2(D, PassedOn),
+    ok.
+
+do_backtrace_depth_2(D, Exc) ->
+    try
+        Exc()
+    catch
+        error:reason:Stk ->
+            if
+                length(Stk) =/= D ->
+                    io:format("Expected depth: ~p\n", [D]),
+                    io:format("~p\n", [Stk]),
+                    error(bad_depth);
+                true ->
+                    ok
+            end
+    end.
+
 line_numbers(Config) when is_list(Config) ->
     {'EXIT',{{case_clause,bad_tag},
              [{?MODULE,line1,2,
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