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erlangstack-traceinlining

Missing entries in the stack trace in Erlang

When I compile the following module:

-module(x).
-export([inp/0]).

f(X) ->
    g(X).

g(X) ->
    error(X).

inp() ->
    f(123).

And evaluate x:inp() I get the following output:

[{x,g,1,[{file,"x.erl"},{line,8}]},
 {erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,689}]},
 {erl_eval,try_clauses,8,[{file,"erl_eval.erl"},{line,919}]},
 {shell,exprs,7,[{file,"shell.erl"},{line,686}]},
 {shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
 {shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]

Where did the calls to f and inp go? This behavior makes it significantly harder to track the causes of errors in my case, how can I get the full stacktrace?

I am using OTP24

Solution

  • This is because of Erlang's compiler optimization. The compiler deduces that, in this specific case, functions f() and inp() are only used to pass a number to function g() and they cannot be used for anything else, not even theoretically. So the compiler "optimizes them away" and de facto only compiles function g().