[lldb] Name UnsafePointer's single child 'pointee'

[kastiglione]

Currently, the builtin formatter for UnsafePointer and UnsafeMutablePointer provide a single child, which is named [0]. This changes that child to be named pointee. This has two advantages:

First, it enables v ptr.pointee to work, which matches p ptr.pointee. This is typically how unsafe pointers access their contents, not via subscript.

Second, it avoids a behavior that looks like a bug to the user. For example:

let ptr = UnsafeMutablePointer<Int>.allocate(capacity: 2)
ptr[0] = 41
ptr[1] = 23
print(ptr) // break here

On that last line, running v ptr produces:

(lldb) v ptr
(UnsafeMutablePointer<Int>) ptr = 0x100404080 {
  [0] = 41
}

Both UnsafePointer and UnsafeMutablePointer will only ever print the single child. A user may think their data is wrong, when it's in fact correct (because they aren't shown the second value). Or, they might think lldb has a bug, when in fact printing a single child expected behavior. Unless I have missed something, Unsafe(Mutable)?Pointer does not capture state that would indicate it was created with a specific capacity, that information is "erased". If a capacity were available at runtime, lldb could print all of the children.

Note that with this change v ptr[0] still succeeds, so that behavior is maintained. Also note that v ptr[1] does not currently work regardless of whether it's valid. This is because the provider reports only 1 child. The work around is to run p ptr[1].

After this change, the above v command prints:

(lldb) v ptr
(UnsafeMutablePointer<Int>) ptr = 0x100404080 {
  pointee = 41
}

rdar://83155374

[kastiglione]

@swift-ci test

[kastiglione]

@swift-ci test

[adrian-prantl]

That's a nice ergonomics improvement!

[augusto2112]

LGTM!

[kastiglione]

@swift-ci test

[kastiglione]

@swift-ci test