Change the deprecation message for null attribute values

[mpdude]

Q	A
Bug fix?	no
New feature?	yes
Deprecations?	no
Documentation?	no
Issues	First step towards #3261, final fix can only happen in 3.x
License	MIT

This PR changes the announcement of what null attribute values will mean in 3.x.

The plan towards fixing #3261 is as follows:

In 2.x:

• null values are treated as true, giving the deprecation notice
• Users need to pass true to keep the current behavior and make the notice go away

In 3.x:

• Make a null value (as well as false) omit the attribute
• aria-* attributes with a false value will trigger a deprecation notice, saying that it will be "false" in 4.0. To omit the aria-* attribute, null shall be used and will make the notice go away.

In 4.x:

• For aria-*, convert false to "false", to be in line with true => "true", closing [TwigComponent] Reconsider behaviour for (bool) false value for ARIA attributes #3261.

[smnandre]

Not sure we should precise the key... I mean maybe we should not suggest passing null is deprecated for that attribute only.

"To keep the current result, pass true instead."

I think with the various changes we plan, we should avoid using "current" / "previous" / "next" or maintaining (or reading) the docs will become quickly really hard.

What about something like "Use true to add the attribute, null or false to remove it"

[mpdude]

I will try to reword that.

My initial idea was that it might make it easier for users to understand which attribute to search for. But I also realized that people might be collecting and grouping deprecation messages by type, and so having a different message for each attribute might not be helpful to them either.

Also, for example the XmlFileReader deprecated in Symfony 7.4 only says XML is deprecated but does not give the file name. So, omitting the attribute name will be in line with that.

[mpdude]

Now it's

Passing null as value to set an attribute is deprecated, pass true instead. In 3.0, the null value will remove the attribute.

[Kocal]

Thanks you for working on this!

aria-* attributes with a false value will trigger a deprecation notice, saying that it will be "false" in 4.0 (...)

Couldn't it be done in 3.x?

[mpdude]

Couldn't it be done in 3.x?

I don't think so, but I haven't tried it, only looking at the code.

In 2.x, false means to omit attributes, and null (still) is equal to true (and should print "true" for aria-*).

So if users would get a deprecation notice in 2.x, telling them that false for aria-* would not omit the attribute in 3.0 but print "false" instead – there is no other value that they could migrate to (in 2.x) to keep the effect of omitting the attribute. Remember, null still results in true.

Thus I think we need the change here to give ourselves a little more legroom in 3.0 and something users could switch their aria-*: false values to.

Am I missing something?

[mpdude]

Not sure about test failures, seem unrelated