[confmap] **Discuss** Identify string field type and set the expanded value accordingly

[dloucasfx]

Description

Note: This PR is for discussion as I might be missing something obvious in how the type identification works in confmap. If code owner agreed with the Issue identified and the PR is accepted, I will need to push more changes to cleanup unused code.

Issue: #12793

If you have a config that contains a slice/map of type struct and one of the fields in that struct is an env variable which is set to a numerical value, the collector will fail to start with

Error: failed to get config: cannot unmarshal the configuration: decoding failed due to the following error(s):
error decoding 'extensions': error reading configuration for "headers_setter": decoding failed due to the following error(s):
'headers[0].default_value' expected type 'string', got unconvertible type 'int', value: '12345'

The existing isStringyStructure does not handle structs which causes the first call made to useExpandValue to sanitize "ALL" data input and use the parsed value.

After looking into mapstructure code, I have noticed that the useExpandValue is called on every sub config with the associated data https://github.com/go-viper/mapstructure/blame/main/mapstructure.go#L514-L546
This made me wonder why the extra logic to check the whole structure is needed and that the first block of useExpandValue if exp, ok := data.(expandedValue); ok { should do the job.

Link to tracking issue

I have removed the extra structure type check and some and fixed the string pointer edge case.
Added an extra unit test that exposes the issue at hand.

Testing

Added a unit test and ran a bunch of manual tests

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 91.45%. Comparing base (55f569d) to head (0b87bc4).
Report is 51 commits behind head on main.

Files with missing lines	Patch %	Lines
confmap/confmap.go	40.00%	2 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (40.00%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12860      +/-   ##
==========================================
- Coverage   91.46%   91.45%   -0.02%     
==========================================
  Files         493      493              
  Lines       26984    26968      -16     
==========================================
- Hits        24682    24663      -19     
- Misses       1818     1820       +2     
- Partials      484      485       +1     

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[github-actions]

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