Handle empty indexes for slices and arrays (eg. field[]=1&field[]=2)

[mfly]

Fixes Or Enhances

Related to: #60

This PR introduces support for parsing arrays with trailing square brackets (field[]=1&field[]=2).

This format is quite widespread and supported by numerous FE and BE frameworks.

Make sure that you've checked the boxes below before you submit PR:

• Tests exist or have been written that cover this particular change.

@go-playground/admins

[coveralls]

coverage: 99.817% (+0.003%) from 99.814%
when pulling fb76283 on mfly:mm-handle-empty-slice-index
into 8785d3c on go-playground:master.

[deankarn]

@mfly TY for the PR and I would like to support this.

I wonder if this can be abstracted away during parsing within parseMapData if possible though to keep the setFieldByType as simple as possible?

[mfly]

Hi @deankarn, thanks for expressing your interest in this. I've considered three options:

1. Preprocess the url.Values by merging keys ending with [] suffix with the respective keys without the suffix - pretty straightforward way to fix the issue, but breaks existing usages like this one
2. changes in parseMapData - I attempted that, but it seemed out of place and I encountered some problems with namespaces
3. the proposed approach - pretty simple, explicit and clean. Works with all the use cases I came up with

If you don't like the current approach I can revisit 2. at some point. Happy to take any suggestions you may have.