rustdoc: Feature request: Also render the alignment under --show-type-layout

[solarretrace]

Problem

It can be tedious to query the size/alignment of non-generic types (struct, enum, union), which one might want to do for many reasons. Currently, you have to do one of the following:

1. Compile a crate that has access to the type in question and print the value.
2. Print the value from the playground, if the crate is available there (which probably wont be the case for anything you're currently working on.)
3. Inspect compiler output via -Zprint-type-sizes.

All of these have the problem of having to compile code to get an answer.

Proposed Solution

The ideal solution would be to display the size & alignment of types in the cargo doc generated output, so you wouldn't have to build a crate.

Notes

I have no idea how feasible this is, but given that cargo doc already compiles and runs doc tests, it doesn't seem unreasonable.

[ehuss]

Does --show-type-layout work for you?

[fmease]

Well, I guess --show-type-layout doesn't render alignments at the time of writing, only sizes.

[solarretrace]

It's certainly a step in the right direction. The only problem being that it's not a default option, so if docs weren't built with --show-type-layout, you still have to download the crate and generate the docs for it, (which is the tedium I am trying to avoid.)

[solarretrace]

Thinking about it a bit more, and I'm realizing that this may actually be the best I can hope for, just because size & alignment don't depend only on the compiler version, but also the compile target -- which would preclude this from just being useful as only size + alignment. Tabulating size + alignment for different platforms seems like a much larger request, so I suppose I'll just have to take what we have...