Summary:
(Copied from https://www.internalfb.com/diff/D46606060)
This diff makes its files safe for use with -Wimplicit-fallthrough. Now that we're using C+20 there's no reason not to use this C++17 feature to make our code safer.
It's currently possible to write code like this:
```
switch(x){
case 1:
foo1();
case 2:
foo2();
break;
case 3:
foo3();
}
```
But that's scary because we don't know whether the fallthrough from case 1 was intentional or not.
The -Wimplicit-fallthrough flag will make this an error. The solution is to either fix the bug by inserting break or indicating intention by using [[fallthrough]]; (from C++17).
```
switch(x){
case 1:
foo1();
[[fallthrough]]; // Solution if we intended to fallthrough
break; // Solution if we did not intend to fallthrough
case 2:
foo2();
break;
case 3:
foo3();
}
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/11663
Test Plan: Existing tests
Reviewed By: jowlyzhang
Differential Revision: D47961248
Pulled By: jaykorean
fbshipit-source-id: 0d374c721bf1b328c14949dc5c17693da7311d03
Jay Huh