ReferenceError: Cannot access 'FALLBACK_OTEL_TRACES_SAMPLER' before initialization

[weyert]

Please answer these questions before submitting a bug report.

What version of OpenTelemetry are you using?

0.19

What version of Node are you using?

14.5.0

Please provide the code you used to setup the OpenTelemetry SDK

N/A

What did you do?

I am trying to run some unit tests in CI and Jest was throwing this error:

[test]     ReferenceError: Cannot access 'FALLBACK_OTEL_TRACES_SAMPLER' before initialization
[test] 
[test]       at buildSamplerFromEnv (node_modules/@opentelemetry/tracing/src/config.ts:75:89)
[test]       at Object.<anonymous> (node_modules/@opentelemetry/tracing/src/config.ts:37:12)
[test]       at Object.<anonymous> (node_modules/@opentelemetry/tracing/src/utility.ts:17:1)

If possible, provide a recipe for reproducing the error.

What did you expect to see?

I would expect this error is not happening :)

What did you see instead?

An runtime error is thrown

Additional context

Mostly a ticket to remind myself to look into this issue. Probably need to move the declaring of FALLBACK_OTEL_TRACES_SAMPLER above the function buildSamplerFromEnv

[dyladan]

FALLBACK_OTEL_TRACES_SAMPLER is already declared above buildSamplerFromEnv...

From the code I'm looking at this should definitely not be happening. I wonder if either tsc or webpack is doing some mangling? What tests were causing this? I haven't seen this failure in our CI yet.

[weyert]

Oh these our my project's tests :)

[dyladan]

I think this might be a bug with your program, not with our library. Can you provide a repro?

edit: we should do our best not to crash even with incorrect usage so this is definitely something we want to look into even if it isn't a "bug"

[weyert]

I was thinking this call is problematic:

opentelemetry-js/packages/opentelemetry-tracing/src/config.ts

Line 37 in c516264

sampler: buildSamplerFromEnv(env),

As it calls buildSamplerFromEnv which uses FALLBACK_OTEL_TRACES_SAMPLER but FALLBACK_OTEL_TRACES_SAMPLER is not defined above DEFAULT_CONFIG.

But yeah, I agree it should not crash and probably I am doing something silly like using OTEL env variables :)
I will do some digging next week

[dyladan]

you're right. easy to fix though

[dyladan]

#2171

[dyladan]

JS function hoisting hoists the function getConst but does not hoist the const being returned. Even though it appears in the code that the const is declared before the function, during runtime it is actually not.