Support default values for env var expansion

[yurishkuro]

Description

Support shell-style default value and error message for env var expansion.

// A default value for unset variable can be provided after :- suffix, for example:
// `env:NAME_OF_ENVIRONMENT_VARIABLE:-default_value`

Link to tracking issue

Fixes #5228

Testing

Unit tests

Documentation

• Provider Go docs
• Probably needs some other docs changes?

[TylerHelmuth]

I'd like to make sure we're in alignment with the configuration sig on the syntax before merging this

[yurishkuro]

@TylerHelmuth I though that was settled, per #5228 (comment)

The OpenTelemetry Configuration WG now admits the shell syntax for the SDK configuration files. Since we aim to be aligned with them, it makes sense in my opinion to add support in the Collector for this as well.

[yurishkuro]

@mx-psi is Configuration WG decision on shell syntax documented / implemented somewhere?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.90%. Comparing base (b10029c) to head (4d741e7).
Report is 87 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10907      +/-   ##
==========================================
+ Coverage   91.89%   91.90%   +0.01%     
==========================================
  Files         411      411              
  Lines       19311    19320       +9     
==========================================
+ Hits        17745    17756      +11     
+ Misses       1217     1216       -1     
+ Partials      349      348       -1     

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[mx-psi]

@mx-psi is Configuration WG decision on shell syntax documented / implemented somewhere?

Yup, see https://opentelemetry.io/docs/specs/otel/configuration/file-configuration/#environment-variable-substitution

[mx-psi]

Note that the :?error syntax is not supported by the Configuration WG. I am in favor of it, but it would be good to at least check that the Configuration WG is not vehemently opposed to eventually adding that

[codeboten]

I'm not aware of a definition for setting an error message, is there an open issue somewhere?

[yurishkuro]

I think we should still have it. I don't understand the approach "let's be like Shell but just different enough so that common things don't work".

[codeboten]

not disagreeing, this was me asking if there is already a discussion about this somewhere I haven't found yet

[mx-psi]

I don't understand the approach "let's be like Shell but just different enough so that common things don't work".

This doesn't mean that we need to add full support for Bash/POSIX-like syntax today. Your PR does not add full support for all the features that Bash supports and that's okay. As I said above, I am not opposed to adding this, but since alignment with the Configuration WG is an explicit goal we should bring it up on their repo first.

[yurishkuro]

I removed error syntax -- 3a3f939.

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.