Unable to build minimal example with no_std

[dignifiedquire]

Describe the Bug

When trying to build a minimal example with no_std unfortnately it does not compile with 0.2.78

Steps to Reproduce

# Cargo.toml
[package]
name = "hello-wasm"
version = "0.1.0"

[lib]
crate-type = ["cdylib"]

[dependencies]
wasm-bindgen = { version = "0.2.78", default-features = false }

// src/lib.rs
![no_std]

extern crate wasm_bindgen;
use wasm_bindgen::prelude::*;

#[panic_handler]
fn panic(_panic: &core::panic::PanicInfo<'_>) -> ! {
    loop {}
}

#[wasm_bindgen]
extern "C" {
    fn alert(s: &str);
}

#[wasm_bindgen]
pub fn greet() {
    alert("Hello world!");
}

Expected Behavior

It compiles.

Actual Behavior

Error log (both 1.57.0 nightly and 1.51.0 produce the same error

 cargo build --target wasm32-unknown-unknown
   Compiling wasm-bindgen v0.2.78
error[E0433]: failed to resolve: use of undeclared crate or module `mem`
   --> /Users/dignifiedquire/.cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/wasm-bindgen-0.2.78/src/convert/slices.rs:232:9
    |
232 |         mem::transmute::<Box<[u8]>, Box<str>>(<Box<[u8]>>::from_abi(js))
    |         ^^^ use of undeclared crate or module `mem`

error[E0433]: failed to resolve: could not find `externref` in the crate root
    --> /Users/dignifiedquire/.cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/wasm-bindgen-0.2.78/src/lib.rs:1482:16
     |
1482 |         crate::externref::link_intrinsics();
     |                ^^^^^^^^^ could not find `externref` in the crate root

error[E0412]: cannot find type `Box` in this scope
   --> /Users/dignifiedquire/.cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/wasm-bindgen-0.2.78/src/convert/slices.rs:103:27
    |
103 |               type Anchor = Box<[$t]>;
    |                             ^^^ not found in this scope
...
128 | / vectors! {
129 | |     u8 i8 u16 i16 u32 i32 u64 i64 usize isize f32 f64
130 | | }
    | |_- in this macro invocation
    |
    = note: this error originates in the macro `vectors` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0412]: cannot find type `Box` in this scope
   --> /Users/dignifiedquire/.cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/wasm-bindgen-0.2.78/src/convert/slices.rs:106:54
    |
106 |               unsafe fn ref_from_abi(js: WasmSlice) -> Box<[$t]> {
    |                                                        ^^^ not found in this scope

[jonboj]

Tried to reproduce on Ubuntu 21.04
When building the above with >wasm-pack build --debug --target web
get error
error[E0152]: found duplicate lang item panic_impl
--> src/lib.rs:7:1
|
7 | fn panic(panic: &core::panic::PanicInfo<'>) -> ! {

When the panic function is removed this builds successfully.

[dignifiedquire]

got the same error when I removed everything in the file, except the no_std line (macos)

[jonboj]

Could indicate some misconfiguration in the tool-chain. Maybe start with a minimal working project and then introduce #![no_std]

[dignifiedquire]

I have reduced it to the absolute minimum I could:

• empty lib.rs
• building with cargo build --target wasm32-unknown-unknown --release
• with wasm-bindgen: default-features = true, everything builds fine
• with wasm-bindgen: default-features = false, errors as described above

[jonboj]

On Ubuntu 21.04
Have reproduced, the error above, but the error persist even without #![no_std] in lib.rs. So seems triggerede by wasm-bindgen = { version = "0.2.78", default-features = false } in Cargo.toml.

[alexcrichton]

At this time this crate doesn't support no_std. The idea was to add it at some point but it never panned out. I unfortunately just haven't gotten around to removing it yet.

[dignifiedquire]

I see, thanks

[bhgomes]

@alexcrichton It seems like you would only need to make sure imports come from core and alloc instead of std to support no_std. I can give it a try in a PR if the other maintainers aren't already planning on doing it.