WASI compilation?

[Timmmm]

I'm trying to compile this for wasm32-wasip2 and not getting very far. Do you guys know if this is possible? I got as far as:

rustup toolchain install nightly
rustup +nightly target add wasm32-wasip2
rustup component add rust-src rustc-dev llvm-tools-preview

git clone https://github.com/rust-lang/rustfmt.git
cd rustfmt

rustup override set nightly

cargo build --release --target wasm32-wasip2

However the first error is:

   Compiling rustfmt-nightly v1.8.0 (C:\workspace\rustfmt)
error[E0463]: can't find crate for `rustc_ast`
 --> src\lib.rs:8:1
  |
8 | extern crate rustc_ast;
  | ^^^^^^^^^^^^^^^^^^^^^^^ can't find crate
  |
  = help: maybe you need to install the missing components with: `rustup component add rust-src rustc-dev llvm-tools-preview`

(I have already tried the suggestion.)

Seems like @alexcrichton got this to work a long time ago - see #4358.

[Timmmm]

Ah I think the issue is rustup component add ... rustc-dev adds it for the native architecture. I need rustc-dev for wasm32-wasip2 but it doesn't seem to be available. I guess I'll need to build it from source somehow...

[ytmimi]

I'm not sure if this is possible. Also, rustfmt dynamically links against some rustc internals, and I'm not sure if that's going to cause you any issues when you actually go to run rustfmt.

[Timmmm]

Does it really dynamically link against rustc? Can you point me to the code if so?

I've got pretty far into the compilation (279/290) with this addition to Cargo.toml:

# Rustc dependencies are loaded from the sysroot, Cargo doesn't know about them.

# For WASI however we need to compile them from source since the Rust compiler
# isn't built for WASI.
rustc_ast = { git = "https://github.com/rust-lang/rust.git" }
rustc_ast_pretty = { git = "https://github.com/rust-lang/rust.git" }
rustc_builtin_macros = { git = "https://github.com/rust-lang/rust.git" }
rustc_data_structures = { git = "https://github.com/rust-lang/rust.git" }
rustc_errors = { git = "https://github.com/rust-lang/rust.git" }
rustc_expand = { git = "https://github.com/rust-lang/rust.git" }
rustc_parse = { git = "https://github.com/rust-lang/rust.git" }
rustc_session = { git = "https://github.com/rust-lang/rust.git" }
rustc_span = { git = "https://github.com/rust-lang/rust.git" }
# thin_vec = { git = "https://github.com/rust-lang/rust.git" }

# For WASI we need to enable the nightly feature of `tempfile` (used by rustc)
# so that it can use the wasip2 feature.
tempfile = { version = "*", features = ["nightly"] }

Current error is:

error[E0425]: cannot find function `current_dll_path` in this scope
   --> C:\Users\Tim\.cargo\git\checkouts\rust-a4081372e9049d90\d93f678\compiler\rustc_session\src\filesearch.rs:164:16
    |
164 |     let path = current_dll_path().and_then(|s| try_canonicalize(s).map_err(|e| e.to_string()));
    |                ^^^^^^^^^^^^^^^^ not found in this scope

I guess I will have to do some hackery on rustc unfortunately.

[ytmimi]

It's the rustc_driver I believe. I don't remember all the details, but it's the reason that we can't easily distribute a standalone binary for rustfmt outside of rustup since you need to have the correct tool chain installed.

[Timmmm]

That's unfortunate. Do you know if there are any plans to disentangle rustfmt from rustc?

[ytmimi]

Not to my knowledge, no.