Compile to wasm32-unknown-unknown / Compile without terminal_size

[Boshen]

I'm currently stuck upgrading to v7 for wasm builds.

Background

After the terminal_size upgrade from #308, it brought in an extra dependency rustix, which in turn brought in errrno which doesn't support compile to wasm32-unknown-unknown.

error[E0583]: file not found for module `sys`
  --> /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/errno-0.3.8/src/lib.rs:26:1
   |
26 | mod sys;
   | ^^^^^^^^
   |
   = help: to create the module `sys`, create file "/home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/errno-0.3.8/src/sys.rs" or "/home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/errno-0.3.8/src/sys/mod.rs"
   = note: if there is a `mod sys` elsewhere in the crate already, import it with `use crate::...` instead

After looking at both crates terminal_size and errno, both crates claims they don't support wasm.

Possible Solution

Given that terminal_size is only called when terminal width is not provided, I think it's reasonable to put it behind a feature flag.

miette/src/handler.rs

Lines 374 to 381 in 75fea09

	pub(crate) fn get_width(&self) -> usize {
	self.width.unwrap_or_else(|| {
	terminal_size::terminal_size()
	.unwrap_or((terminal_size::Width(80), terminal_size::Height(0)))
	.0
	.0 as usize
	})
	}

[zkat]

I'm ok putting it behind a feature flag but make it default as part of the fancy feature. Perhaps we can have a fancy-wasm that's specifically wasm-compatible?

[zkat]

(that is, I'll take a patch to make these changes, and I can do a release after that for you)

[Boshen]

I have a few projects that are targeting wasm and wasi.

I'd like to add a syscall feature to make it future compatible.

In this way we can put all syscall related functionalities into a module and guard it at the top level. This will also move all the #[cfg(miri)] / #[cfg(not(miri))] to a single place.

This will also resolve issues like #326 where I want to explicitly control all syscalls.

I'll draft a PR and see how it looks.

[Boshen]

I drafted a PR in #349