feature request: control merging behavior

[grount]

When a user loads multiple YAML files that have the same key with different types the last type loaded is deciding the loaded type.
For example:
first.yml

key: value

second.yml

key: [1,2,3]

The loaded value into the key field will be [1,2,3] if second.yml will be loaded last.
I would like to control the behavior that it could be "loss" with the current behavior and "strict" with type enforcing in the merge.

If it makes sense, I could try to work on it with some guidance 👍
Or if it already exists, I'd appreciate the 'how-to'.

[knadh]

Yep, the current behaviour is to overwrite the previous values in subsequent merges. To add type checks and other similar features, roughly:

• Add a NewWithConf(delim, koanf.Conf{}) that takes a new koanf.Conf{} that can contain arbitrary feature flags.
• koanf.Config { bool StrictMerge }
• Make merge() behave differently based on this config value.
• Will probably need a MergeStrict() in the maps package as well.

[grount]

Thank you for the quick response!
Should I merge the delim field in the new koanf.Config?

[knadh]

Ah yes, makes sense.

[grount]

maps.MergeStrict has to return an error since the merging process can fail.
In koanf, merge is used in 4 places:

1. Load - can return an error.
2. Cut - cannot return an error - but okay since it's a subset.
3. Merge - cannot return an error - possible mergeStrict errors.
4. MergeAt - cannot return an error - possible mergeStrict errors.

As I see it since the koanf.Conf has MergeStrict: true it should affect all the merging behavior across koanf.

Possible solutions:

1. We can either exclude koanf.Merge and koanf.MergeAt by adding koanf.MergeStrict and koanf.MergeStrictAt and ignore the koanf.Conf
2. We can ignore MergeStrict flag in koanf.Merge and koanf.MergeAt functions
3. Change koanf.Merge and koanf.MergeAt signatures so it will return an error. I think it will not break backward compatibility.

I'm up for number 3, WDYT?

[knadh]

3 is the cleanest approach. We can bump the version to 1.0.0 after this. Long overdue.

[grount]

Merging between JSON and YAML will fail because of the float64/int issue.
We can either say that you cannot MergeStrict between YAML and JSON and the recommended way is to use mergeStrict between the same types, or we can check if float64 is a whole number and convert to int but it will not cover cases where user-defined a whole float number: 3.0 but we can only patch one case where in the future there could be more of them.