expression: add implicit eval int and real for function dayname (#21806)

[ti-srebot]

cherry-pick #21806 to release-4.0

---

What problem does this PR solve?

Issue Number: close #19992

Problem Summary:

It's a bit long story.

MySQL has a weird behavior about function dayname() (IMO this apparently is a MySQL defect):

mysql> select dayname("1962-03-01")+1;
+-------------------------+
| dayname("1962-03-01")+1 |
+-------------------------+
|                       4 |
+-------------------------+

It evaluates as integer directly despite the function signature is actually string. Quoted of comments in MySQL source code:

TS-TODO: Item_func_dayname should be derived from Item_str_func.
In the current implementation funny things can happen:
select dayname(now())+1 -> 4

PR #9975 fixed this issue by removing the implicit cast from dayname() string to int/real, however introduced a more obvious bug:

mysql> select cast(dayname('2016-03-08') as double);                                                                                                                                                                                                                            
+---------------------------------------+                                                                                                                                                                                                                                       
| cast(dayname('2016-03-08') as double) |                           
+---------------------------------------+                                                                                               
| Tuesday                               |                           
+---------------------------------------+                                                                                                                                                                                                                                       

As shown above, unconditionally removing implicit cast gave the wrong result for non-arithmetic expressions involving function dayname().

What is changed and how it works?

What's Changed:

Don't use hasSpecialCasts anymore. Instead, mark dayname() as CanImplicitEvalInt/Real, and do "implicit" evalInt/Real in the actual cast functions.

Besides, since filter operator has its own path to evaluate expressions into boolean, modify it too to do "implicit" evalInt/Real.

How it Works:
Adding implicit evalInt/Real path makes cast functions directly evaluate dayname() as int/real, which further involve into whatever evaluation in the upper level of the expression tree.

Related changes

• PR to update pingcap/docs/pingcap/docs-cn: none
• Need to cherry-pick to the release branch: release-4.0

Check List

Tests

• Unit test

Side effects

• Performance regression
  • Consumes more CPU

Release note

• Fix compatibility issue with MySQL for function dayname

[ti-srebot]

/run-all-tests

[ti-srebot]

@zanmato1984 you're already a collaborator in bot's repo.

[qw4990]

Please resolve conflicts @zanmato1984

[qw4990]

Could you please help to resolve conflicts? @ichn-hu @lzmhhh123

[qw4990]

LGTM

[qw4990]

/run-all-tests

[qw4990]

/run-all-tests

[qw4990]

/run-unit-test

[qw4990]

/run-unit-test

[qw4990]

/run-unit-test