Bound environment variables get written to disk

[darrellwarde]

Preflight Checklist

• I have searched the issue tracker for an issue that matches the one I want to file, without success.
• I am not looking for support or already pursued the available support channels without success.
• I have checked the troubleshooting guide for my problem, without success.

Viper Version

1.19.0

Go Version

1.22.5

Config Source

Flags, Environment variables, Files

Format

JSON

Repl.it link

https://replit.com/@darrellwarde/Viper-example

Code reproducing the issue

No response

Expected Behavior

Upon writing config files, I would expect that only the following configuration values would be written to disk:

• Default configuration values
• Values already set in the configuration file
• Values explicitly set using Viper.Set()

Actual Behavior

Configuration values from mapped environment variables get written to configuration file if they have values whilst writing config files. This is unexpected because you generally only expect environment variables to effect the behaviour of executions for which they are set, but because of this, they will be persisted to disk and still act as the configuration values when the variables are no longer set.

In the Repl.it, use the shell to set YEARS_SINCE_BORN during execution. Even though age is never explicitly set in the config, it gets written to the config file purely from the environment variable being set during execution.

Steps To Reproduce

No response

Additional Information

No response

[github-actions]

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[sagikazarmark]

Appreciate the detailed report @darrellwarde !

I don't think config writing has ever been a well-thought-out feature. I agree with your expectation, but others may use it as sort of a "dump" feature for any configuration they have which makes changing behavior like this extremely hard to change.

One thing we could do is make it configurable, defaulting to the current behavior. For example, allow passing a bit mask to Viper that tells it which config sources should be included in the written config.

Would you be open to creating a PR?