When adding a JSON "Custom file" double quotes are added before the first and last squiggly brackets and syntax breaks.

For example, when adding the following composer.json to install mockery in a project,

{
"require":

{ "mockery/mockery": "dev-master" }

}

first and last quotes are added like,

"{
"require":

{ "mockery/mockery": "dev-master" }

}"

and when running "php composer.phar install" it fails with,

[Seld\JsonLint\ParsingException]
"composer.json" does not contain valid JSON