no_std build with pest_derive fails

[jzbor]

Describe the bug
I get the following error, when trying to build with no_std:

   Compiling lash v0.3.1 (/home/jzbor/Programming/Rust/lash)
error: cannot find macro `format` in this scope
  --> src/typing.rs:48:13
   |
48 |             format!("{}", ('A' as usize + n) as u8 as char)
   |             ^^^^^^

error: cannot find macro `format` in this scope
  --> src/typing.rs:50:13
   |
50 |             format!("T{}", n)
   |             ^^^^^^

error: cannot find macro `format` in this scope
   --> src/typing.rs:154:58
    |
154 |             Variable(x) => Ok(self.inst(env.get(x).ok_or(format!("unable to instantiate {}", x))?.clone())),
    |                                                          ^^^^^^

error: cannot find macro `format` in this scope
   --> src/typing.rs:126:13
    |
126 |         Err(format!("unable to unify {} with {}", t1, t2))
    |             ^^^^^^

error: cannot find macro `format` in this scope
  --> src/typing.rs:77:21
   |
77 |                 Err(format!("occurs check failed - {} versus {}", tv.borrow(), tv2.borrow()))
   |                     ^^^^^^

error: cannot find macro `format` in this scope
  --> src/typing.rs:65:21
   |
65 |                 Err(format!("occurs check failed - {} == {}", tv.borrow(), tv2.borrow()))
   |                     ^^^^^^

error[E0433]: failed to resolve: could not find `std` in the list of imported crates
  --> src/parsing.rs:17:10
   |
17 | #[derive(Parser)]
   |          ^^^^^^ could not find `std` in the list of imported crates
   |
   = note: this error originates in the derive macro `Parser` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0433]: failed to resolve: could not find `std` in the list of imported crates
  --> src/parsing.rs:17:10
   |
17 | #[derive(Parser)]
   |          ^^^^^^ could not find `std` in the list of imported crates
   |
   = note: this error originates in the derive macro `Parser` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider importing this module
   |
3  + use core::result;
   |

For more information about this error, try `rustc --explain E0433`.
error: could not compile `lash` (lib) due to 8 previous errors

To Reproduce
Clone https://github.com/jzbor/lash/tree/pest
Run cargo build --lib --no-default-features

Expected behavior
From what I understand this is a supported setup, so it should just build and use core and alloc where necessary.

[tomtau]

For pest and pest_derive: https://github.com/jzbor/lash/blob/pest/Cargo.toml#L23

they should be specified with

pest = { version = "2.7.14", default-features = false }
pest_derive = { version = "2.7.14", default-features = false }

I believe when one calls cargo build --lib --no-default-features, it only applies that --no-default-features to the crate that's being built, not recursively to its dependencies. In the features, it should also specify this:

[features]
default = ["std"]
std = [ "rustyline", "clap", "colored", "humantime", "pest/std", "pest_generator/std" ]

so that the std feature is on by default for pest dependencies in that crate.

[jzbor]

Thanks a lot, I forgot about that...

[jzbor]

Hm, now I get "could not find 'alloc' in the list of imported crates" on the #[derive(Parser)]

[jzbor]

Maybe I have to build alloc in the crate, I'll see...

[jzbor]

Hm I tried with my OS crate, which builds alloc, but I get the same issue

[tomtau]

Maybe cargo needs some extra flags to be passed? e.g.

 cargo build -j1 -Z build-std=core,alloc --lib --no-default-features

instead of just cargo build --lib --no-default-features