Allow respect_cache_headers to be "false"

[Nyholm]

This PR adds a test for an issue I found.

We define respect_cache_headers like:

->enumNode('respect_cache_headers')
    ->info('Whether we should care about cache headers or not [DEPRECATED]')
    ->values([null, true, false])
    ->beforeNormalization()
        ->always(function ($v) {
            @trigger_error('The option "respect_cache_headers" is deprecated since version 1.3 and will be removed in 2.0. Use "respect_response_cache_directives" instead.', E_USER_DEPRECATED);

            return $v;
        })
    ->end()
->end()

On Symfony 2.8, the EnumNode runs array_unique over the possible values. Though, null and false is treated the same. See https://3v4l.org/KWuNP

This will result in that the possible values for respect_cache_headers will only be true and null. This issue will break BC since we promise that all previous configuration will work on newer versions.

FYI: In the last release we defined the respect_cache_headers like:

->scalarNode('respect_cache_headers')->defaultTrue()->end()

[Nyholm]

@stof, have you seen this issue before? Do you know a workaround?

[stof]

hmm, I think the enumNode was always used with strings until now, which is why such issue was never spotted before

[Nyholm]

Thank you. I use a ScalarNode for this now.

[stof]

this one should be indented inside ->validate

[Nyholm]

Thank you

[stof]

the end call should be unindented to make the tree structure visual. This is the end of ->beforeNormalization()

[stof]

ifNotInArray does not create a new node in the tree (otherwise it would need an end node too). It configures the validation node. So this one should be unindented (it was right before your last update)

[Nyholm]

Sorry, it was me that misunderstood. Thank you.

[Nyholm]

Thank you for the reviews.