[wasi-common]: yanix now returns io::Error directly (#1242)

* Yanix now returns io::Error

This commit may seem somewhat controversial at first, but hear me
out first. Currently, Yanix would return a custom error that's a
wrapper around three other error types returned by various entities
inside Rust's `libstd`. In particular, Yanix's error type would wrap
`io::Error`, `num::TryFromIntError` and `ffi::NulError`. It turns
out that there is a natural conversion between the first and the last
and provided by the standard library, i.e., `From<ffi::NulError> for io::Error`
is provided. So at the surface it may seem that only the first two
wrapped error types are worth keeping.

Digging a little bit deeper into `libstd`, `num::TryFromIntError`
is essentially speaking only a marker that the integral conversion
went wrong. The struct implementing this error stores a unit type,
and nothing more. It therefore seems like a waste to wrap this
particular error when we could unify everything under `io::Error`.
And so, whenever we perform an int conversion, I suggest we simply
remap the error to `io::Error::from_raw_os_error(libc::EOVERFLOW)`
since this carries a comparable amount of information.

As a result of completely discarding `yanix::Error` custom error type,
we are invariably simplifying `yanix` itself, but also allowing
`wasi-common` to simplify in several places as well.

* Adapt wasi-common to changes in yanix

* Add Cargo.lock

* Unwrap try_into's where possible

* Remove unnecessary type annotation

crates/wasi-common/yanix/src/sys/linux/dir.rs

@@ -1,8 +1,8 @@
-use crate::{
-    dir::{Dir, Entry, EntryExt, SeekLoc},
-    Result,
+use crate::dir::{Dir, Entry, EntryExt, SeekLoc};
+use std::{
+    io::{Error, Result},
+    ops::Deref,
 };
-use std::{io, ops::Deref};
 
 #[derive(Copy, Clone, Debug)]
 pub(crate) struct EntryImpl(libc::dirent64);
@@ -26,17 +26,17 @@ impl EntryExt for Entry {
 }
 
 pub(crate) fn iter_impl(dir: &Dir) -> Option<Result<EntryImpl>> {
-    let errno = io::Error::last_os_error();
+    let errno = Error::last_os_error();
     let dirent = unsafe { libc::readdir64(dir.as_raw().as_ptr()) };
     if dirent.is_null() {
-        let curr_errno = io::Error::last_os_error();
+        let curr_errno = Error::last_os_error();
         if errno.raw_os_error() != curr_errno.raw_os_error() {
             // TODO This should be verified on different BSD-flavours.
             //
             // According to 4.3BSD/POSIX.1-2001 man pages, there was an error
             // if the errno value has changed at some point during the sequence
             // of readdir calls.
-            Some(Err(curr_errno.into()))
+            Some(Err(curr_errno))
         } else {
             // Not an error. We've simply reached the end of the stream.
             None

crates/wasi-common/yanix/src/sys/linux/fadvise.rs

@@ -1,4 +1,5 @@
-use crate::{Error, Result};
+use crate::from_success_code;
+use std::io::Result;
 use std::os::unix::prelude::*;
 
 #[derive(Debug, Copy, Clone)]
@@ -18,5 +19,5 @@ pub unsafe fn posix_fadvise(
     len: libc::off_t,
     advice: PosixFadviseAdvice,
 ) -> Result<()> {
-    Error::from_success_code(libc::posix_fadvise(fd, offset, len, advice as libc::c_int))
+    from_success_code(libc::posix_fadvise(fd, offset, len, advice as libc::c_int))
 }

crates/wasi-common/yanix/src/sys/linux/file.rs

@@ -1,5 +1,7 @@
-use crate::Result;
-use std::{io, os::unix::prelude::*};
+use std::{
+    io::{Error, Result},
+    os::unix::prelude::*,
+};
 
 pub unsafe fn isatty(fd: RawFd) -> Result<bool> {
     let res = libc::isatty(fd);
@@ -8,20 +10,17 @@ pub unsafe fn isatty(fd: RawFd) -> Result<bool> {
         Ok(true)
     } else {
         // ... otherwise 0 is returned, and errno is set to indicate the error.
-        let errno = io::Error::last_os_error();
-        if let Some(raw_errno) = errno.raw_os_error() {
-            // While POSIX specifies ENOTTY if the passed
-            // fd is *not* a tty, on Linux, some implementations
-            // may return EINVAL instead.
-            //
-            // https://linux.die.net/man/3/isatty
-            if raw_errno == libc::ENOTTY || raw_errno == libc::EINVAL {
-                Ok(false)
-            } else {
-                Err(errno.into())
-            }
+        let errno = Error::last_os_error();
+        let raw_errno = errno.raw_os_error().unwrap();
+        // While POSIX specifies ENOTTY if the passed
+        // fd is *not* a tty, on Linux, some implementations
+        // may return EINVAL instead.
+        //
+        // https://linux.die.net/man/3/isatty
+        if raw_errno == libc::ENOTTY || raw_errno == libc::EINVAL {
+            Ok(false)
         } else {
-            Err(errno.into())
+            Err(errno)
         }
     }
 }

crates/wasi-common/yanix/src/sys/linux/mod.rs

@@ -2,7 +2,8 @@ pub(crate) mod dir;
 pub(crate) mod fadvise;
 pub(crate) mod file;
 
-use crate::{dir::SeekLoc, Result};
+use crate::dir::SeekLoc;
+use std::io::Result;
 
 impl SeekLoc {
     pub unsafe fn from_raw(loc: i64) -> Result<Self> {