Duplicate keys in JSON configuration

When using ConfigurationBuilder.AddJsonFile to load settings from a config.json file, there is no exception when the content of the file contains a duplicate key.

To Reproduce

Steps to reproduce the behavior:

1. Using version ‘2.2.0’ of package ‘Microsoft.Extensions.Configuration.Json’
2. Create a configuration file with contents:

{
    "my-duplicate-key": true,
    "my-duplicate-key": false
}

1. Run this code ConfigurationBuilder.AddJsonFile
2. An exception is expected, but the code continues without exception

Expected behavior

An exception should be thrown that there is a duplicate key “my-duplicate-key” in the configuration file.

[gfoidl]

Expected behavior

…or the behavior remains as is, but is documented – right now there is no info in the docs what happens if duplicate keys are present.

[msftbot[bot]]

Paging @dotnet/extensions-migration ! This issue has been revived from staleness. Please take a look and route to the appropriate repository.