While we might never be able to have 100% of our code strict, we can at
the very least do it for all of our tests. This ensures that our tests
are using our API with the types as intended by the test author, and not
silently be cast to what our API requires.
For one of the Phpstan upgrades, some message text had changed so drastically that the only practical solution at the time was to move the messages from phpstan-baseline.neon to phpstan.neon.dist. This was not ideal, but it allowed us time to move on and study the errors, which I have now done. At one point, Parser is expecting a variable to be an array, and that was not clear from the code. If not an array, the code will error out (which was Phpstan's concern); I have changed it to throw an exception instead. This satisfies Phpstan, and I can get the message out of neon.dist (without needing to restore it to baseline). Unsurprisingly, the exception was never thrown in the existing test suite, although I added a couple of tests to exercise that code.
In Helper/Dimension, Phpstan flagged a statement inappropriately. I suppressed the message using an annotation and filed a bug report https://github.com/phpstan/phpstan/issues/7563. A fix for the problem was merged yesterday, which is good, but it puts us in a tenuous position. The annotation is needed now, but, when the fix is inevitably pushed to the version we use, the no-longer-needed annotation will trigger a different message. Recode so that neither the current nor the future versions will issue a message, eliminating the annotation in the process.