This is for lldb, where the `po` command for Swift is implemented in `_DebuggerSupport.stringForPrintObject`.
Up to now, a Swift struct which conforms to `CustomStringConvertible` will print both its `description`, and also recursively print its internals.
This differs from a class, where only the `description` is printed.
This changes `stringForPrintObject` to print only the `description` of value types that conform to `CustomStringConvertible` (or `debugDescription` for `CustomDebugStringConvertible`) – unless the also type conforms to `CustomReflectable`, in which case its children are printed.
This issue was raised for `FilePath`, which prints excessively verbosely, like so:
```
(lldb) po FilePath("/tmp")
▿ "/tmp"
▿ _storage : "/tmp"
▿ nullTerminatedStorage : 5 elements
▿ 0 : SystemChar
- rawValue : 47
▿ 1 : SystemChar
- rawValue : 116
▿ 2 : SystemChar
- rawValue : 109
▿ 3 : SystemChar
- rawValue : 112
▿ 4 : SystemChar
- rawValue : 0
```
rdar://161919005
Dave Lee
b32b74af7c