Some modules support no_std

[k-nasa]

The following three modules have been changed to work with no_std.

• task
• future
• stream

[yoshuawuyts]

This is incredibly cool! @k-nasa what's left for this PR before we can merge?

[k-nasa]

@yoshuawuyts
I think it's nothing. I think it is enough now.

However, I think it is necessary to add no_std examples and documentation in the future.

Or should it be done now?

[k-nasa]

I couldn't build with target thumbv7m-none-eabi.
Looking at build details using cargo -v, it appears to be linked std.

Running `rustc --edition=2018 --crate-name futures_core /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-core-0.3.1/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type lib --emit=dep-info,metadata -C debuginfo=2 --cfg 'feature="alloc"' --cfg 'feature="std"' -C metadata=612df2be1fa85baa -C extra-filename=-612df2be1fa85baa --out-dir /home/runner/work/async-std/async-std/target/thumbv7m-none-eabi/debug/deps --target thumbv7m-none-eabi -L dependency=/home/runner/work/async-std/async-std/target/thumbv7m-none-eabi/debug/deps -L dependency=/home/runner/work/async-std/async-std/target/debug/deps --cap-lints allow -Dwarnings` 

I ran command cargo check --no-default-features --features alloc --target thumbv7m-none-eabi -v.

output is

cargo build --no-default-features --target thumbv7m-none-eabi --features alloc -v Compiling futures-core v0.3.1 Fresh pin-project-lite v0.1.4 Running `rustc --crate-name futures_core --edition=2018 /Users/nasa/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-core-0.3.1/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts --crate-type lib --emit=dep-info,metadata,link -C debuginfo=2 --cfg 'feature="alloc"' --cfg 'feature="std"' -C metadata=bf22d8a7eee34ada -C extra-filename=-bf22d8a7eee34ada --out-dir /Users/nasa/lab/oss/k-nasa/async-std/target/thumbv7m-none-eabi/debug/deps --target thumbv7m-none-eabi -L dependency=/Users/nasa/lab/oss/k-nasa/async-std/target/thumbv7m-none-eabi/debug/deps -L dependency=/Users/nasa/lab/oss/k-nasa/async-std/target/debug/deps --cap-lints allow` error[E0463]: can't find crate for `std` | = note: the `thumbv7m-none-eabi` target may not be installed error: aborting due to previous error For more information about this error, try `rustc --explain E0463`. error: could not compile `futures-core`. Caused by: process didn't exit successfully: `rustc --crate-name futures_core --edition=2018 /Users/nasa/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-core-0.3.1/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts --crate-type lib --emit=dep-info,metadata,link -C debuginfo=2 --cfg 'feature="alloc"' --cfg 'feature="std"' -C metadata=bf22d8a7eee34ada -C extra-filename=-bf22d8a7eee34ada --out-dir /Users/nasa/lab/oss/k-nasa/async-std/target/thumbv7m-none-eabi/debug/deps --target thumbv7m-none-eabi -L dependency=/Users/nasa/lab/oss/k-nasa/async-std/target/thumbv7m-none-eabi/debug/deps -L dependency=/Users/nasa/lab/oss/k-nasa/async-std/target/debug/deps --cap-lints allow` (exit code: 1) 

@taiki-e Do you know any solution?

[taiki-e]

Looks like due to rust-lang/cargo#4866 (cargo leaking *-dependencies into normal build)

Could you add -Z avoid-dev-deps flag for cargo command?

(if we need to run on stable, use cargo-hack's --no-dev-deps flag instead.)

[k-nasa]

@taiki-e Thanks!!
I could build no-std.

[taiki-e]

FYI: to enable these utilities on no-std, use manually implemented futures instead of async functions.

[k-nasa]

Is it a problem to merge this?

[yoshuawuyts]

@k-nasa fantastic work; this is great!

[tirr-c]

@yoshuawuyts it seems like an autocompletion failure? ;)

[yoshuawuyts]

@tirr-c ahaha, oops context switch failure. Was also reviewing Tide patches 😂 sorry sorry!