Base.summarysize misses null byte of String

[tecosaur]

I've recently been working on my About.jl package, for showing more information about the internals/memory representation of Julia values. When looking into strings a bit more, I came across this bit of jl_alloc_string:

julia/src/array.c

Line 301 in e9a24d4

size_t sz = sizeof(size_t) + len + 1; // add space for trailing \nul protector and size

In the REPL, with the 3-codunit string hey, I see this:

julia> ncodeunits("hey")
3

julia> Base.summarysize("hey")
11

Since I'm on a 64-byte system, sizeof(size_t) should be 64-bits/8-bytes, and so 8 + 3 + 1 gives us ... 12, not 11.

It seems like Base.summarysize might be missing the trailing null byte?

[vtjnash]

It also doesn't include padding bytes in the allocator. I guess we should account for the null here though, in case someone is trying to expand their alloc request to fill that padding?