Cannot start observer: (UndefinedFunctionError) function :observer.start/0 is undefined

Questions / Help
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21

Amazing, thank you!

22

Since 1.15, Elixir prunes unused code paths. Adding the following line to project/1 callback of your mix.exs would do.

    prune_code_paths: Mix.env() == :prod,

This hack also works for some other erlang stuff, like common_test I needed in Enfiladex.

1 Like
23

TIL about the Elixir code pruning, thank you!

1 Like
24

This works, but also means youā€™re now only pruning paths in production, so all issues related to it only surface in production.

2 Likes
25

I use 4 environments, the commons and :ci for GHA/CI, in which I donā€™t prune codepaths (and mimic :prod in general.)

26

What can be the potential issues? Sorry, Iā€™m not very knowledgeable about this, can you please elaborate a bit?

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27

Afaik mostly missing out on the speedups code path pruning are meant to bring. But Iā€™ve seens code path pruning affect how you interact with applications you donā€™t explicitly depend on (in dev), like: Observer in iex -S mix - #5 by axelson

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28

Iā€™m reading this too because I couldnā€™t start observerā€¦ :sweat_smile: Speed reasons, understandable.

2 Likes
29

I ran with the same issue with my Mac. Reinstalling Xcode developer tools solved it for me

30

Since I donā€™t see it only this thread, copying the solution referenced to above. Running

apt install -y erlang-observer

solves this error

iex(76)> :observer.start
** (UndefinedFunctionError) function :observer.start/0 is undefined (module :observer is not available)
:observer.start()

on Ubuntu.