std: add doctest to parent_id

[RalfJung]

This operation is currently entirely untested. (I know because it shows up nowhere in the test failures when running the test suite in Miri, and Miri does not support this operation.)

So let's add a test.

[rustbot]

r? @clarfonthey

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[RalfJung]

@rustbot reroll

[joshtriplett]

@bors r+ rollup

[rust-bors]

📌 Commit 5fd1cb6 has been approved by joshtriplett

It is now in the queue for this repository.

[jhpratt]

@bors r- #164179 (comment)

---- library\std\src\os\unix\process.rs - os::unix::process::parent_id (line 753) stdout ----
error[E0432]: unresolved import `std::os::unix`
   --> library\std\src\os\unix\process.rs:754:14
    |
754 | use std::os::unix::process;
    |              ^^^^ could not find `unix` in `os`
    |
note: found an item that was configured out
   --> library\std\src\os\mod.rs:50:17
    |
 49 |     target_family = "unix" => {
    |     ---------------------- the item is gated behind the `unix` feature
 50 |         pub mod unix;
    |                 ^^^^

[rust-bors]

This pull request was unapproved.

This PR was contained in a rollup (#164179), which was unapproved.

View changes since this unapproval

[RalfJung]

How is that possible...? The doctest should only exist if we have the unix target feature?

[RalfJung]

Apparently this was on aarch64-pc-windows-msvc. The entire file should be completely ignored there, no?

Seems like all the other doctests in std::os::unix have a snippet like this

#[cfg_attr(target_family = "unix", doc = "```")]
#[cfg_attr(not(target_family = "unix"), doc = "```ignore (needs unix)")]

It makes no sense at all to me that this should be needed.

[RalfJung]

@bors r=joshtriplett

[rust-bors]

📌 Commit 0103672 has been tentatively approved by joshtriplett

It will be put into the queue for this repository once PR CI succeeds.

[theemathas]

It makes no sense at all to me that this should be needed.

@RalfJung This incantation is the correct one. See #162112 (comment)