Fix: do not display graphiz when argument is set false

[jerowork]

Q	A
Branch	master for features and deprecations
Bug fix?	yes
New feature?	no
BC breaks?	yes
Deprecations?	no
Documented?	yes
Fixed tickets	none

Description

By default, addOptionalArgument in ProcessArgumentsCollection discards an argument when the value evaluates to false.
This results in the absence of the option in the final process command.

In many cases, the absence of an option means false, but in the case of Deptrac's --formatter-graphviz-display it means true.

The use of addOptionalArgument will never allow false, so unsetting this option in Deptrac is impossible.
In Deptrac.php all options are always present, so adding it just by default with add will fix this.

Edit:
Because the default value for this option --formatter-graphviz-display is true at Deptrac itself, the default here should be true too, to align. This means a small BC because the default is different.

Sources

Deptrac: option formatter_graphviz_display is set true by default:

• https://github.com/sensiolabs-de/deptrac#graphviz-formatter

GrumPHP: option formatter_graphviz_display is set false by default:

• https://github.com/phpro/grumphp/blob/master/doc/tasks/deptrac.md#deptrac

[veewee]

Thanks for the detailed PR @jerowork!
The code looks good.

However : I'dd prefer to have the defaults similar to the once of the source tool as well.
Would this be something you could change + document as well?

[jerowork]

@veewee I'd thought of it, but that would change the current default behavior of this parameter when not set in the config.

I am in favour of having the same default values as the source tool, so I will update this PR to align with Deptrac's defaults 👍

[veewee]

Thanks for your work! Looks good!