Support for custom pflags

[unguiculus]

Preflight Checklist

• I have searched the issue tracker for an issue that matches the one I want to file, without success.

Problem Description

It is possible to create custom pflags by implementing the Value interface. The problem is that viper just calls ValueString() on value types it doesn't know about.

I implemented a custom StringToBool flag, which pflags unfortunately lacks. In order for this to work properly, I would need Viper to call a conversion function as is, e.g., done for stringToInt.

Proposed Solution

My suggestion would be to add an option to register custom conversion functions for value types.

func (v *Viper) RegisterValueTypeConvFunc(valueType string, confFunc func(val string) any)

If a function is registered for a value type, Viper would then call this function in the find method.

I would offer to work on this if there is interest.

Alternatives Considered

No response

Additional Information

No response

[github-actions]

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