## Motivation
Looks like the Rust 1.48.0 version of `rustfmt` changed some formatting
rules (fixed some bugs?), and some of the code in `tokio-macros` is no
longer correctly formatted. This is breaking CI.
## Solution
This commit runs rustfmt on Rust 1.48.0. This fixes CI.
Closes#3158
`tokio::test` and related macros now use the absolute path
`::core::prelude::v1::test` to refer to the built-in `test` macro.
This absolute path was introduced in rust-lang/rust#62086.
When using #[tokio::main] on a function with generics, the generics are
skipped. Simply using #vis #sig instead of #vis fn #name(#inputs) #ret
fixes the problem.
Fixes#2176
The Tokio runtime provides a "shell" runtime when `rt-core` is not
available. This shell runtime is enough to support `#[tokio::main`] and
`#[tokio::test].
A previous change disabled these two attr macros when `rt-core` was not
selected. This patch fixes this by re-enabling the `main` and `test`
attr macros without `rt-core` and adds some integration tests to prevent
future regressions.
Eliza Weisman