Change "mixed" declarations to more accurate types in test members; in particular, change those that would be flagged if we were to run Phpstan at level 9 (we currently run level 8). I may or may not follow up with source code (over 700 level-9 problems remain for src), but, as with strict typing, there is no reason to avoid the effort for test members.
It was necessary to update some doc blocks in src to accommodate this change. However, no executable code is touched.
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.
Fix#2897. We have been relying on iconv/mb_convert_encoding to detect invalid UTF-8, but all techniques designed to validate UTF-8 seem to accept FFFE and FFFF. This PR explicitly converts those characters to FFFD (Unicode substitution character) before validating the rest of the string. It also substitutes one or more FFFD when it detects invalid UTF-8 character sequences.
A comment in the code being change stated that it doesn't handle surrogates. It is right not to do so. The only case where we should see surrogates is reading UTF-16. Additional tests are added to an existing test reading a UTF-16 Csv to demonstrate that surrogates are handled correctly, and that FFFE/FFFF are handled reasonably.
oleibman
Adrien Crivelli