[wasi-common]: clean up error handling (#1253)

* Introduce WasiCtxBuilderError error type

`WasiCtxBuilderError` is the `wasi-common` client-facing error type
which is exclusively thrown when building a new `WasiCtx` instance.
As such, building such an instance should not require the client to
understand different WASI errno values as was assumed until now.

This commit is a first step at streamlining error handling in
`wasi-common` and makes way for the `wiggle` crate.

When adding the `WasiCtxBuilderError`, I've had to do two things of
notable importance:
1. I've removed a couple of `ok_or` calls in `WasiCtxBuilder::build`
   and replaced them with `unwrap`s, following the same pattern in
   different builder methods above. This is fine since we _always_
   operate on non-empty `Option`s in `WasiCtxBuilder` thus `unwrap`ing
   will never fail. On the other hand, this might be a good opportunity
   to rethink the structure of our builder, and how we good remove
   the said `Option`s especially since we always populate them with
   empty containers to begin with. I understand this is to make
   chaining of builder methods easier which take and return `&mut self`
   and the same applies to `WasiCtxBuilder::build(&mut self)` method,
   but perhaps it would more cleanly signal the intentions if we simply
   moved `WasiCtxBuilder` instance around. Food for thought!
2. Methods specific to determining rights of passed around `std::fs::File`
   objects when populating `WasiCtx` `FdEntry` entities now return
   `io::Error` directly so that we can reuse them in `WasiCtxBuilder` methods
   (returning `WasiCtxBuilderError` error type), and in syscalls
   (returning WASI errno).

* Return WasiError directly in syscalls

Also, removes `error::Error` type altogether. Now, `io::Error` and
related are automatically converted to their corresponding WASI
errno value encapsulated as `WasiError`.

While here, it made sense to me to move `WasiError` to `wasi` module
which will align itself well with the upcoming changes introduced
by `wiggle`. To different standard `Result` from WASI specific, I've
created a helper alias `WasiResult` also residing in `wasi` module.

* Update wig

* Add from ffi::NulError and pass context to NotADirectory

* Add dummy commit to test CI

crates/wasi-common/src/wasi.rs

@@ -10,6 +10,115 @@ use wig::witx_wasi_types;
 
 witx_wasi_types!("snapshot" "wasi_snapshot_preview1");
 
+pub type WasiResult<T> = Result<T, WasiError>;
+
+#[derive(Clone, Copy, Debug, thiserror::Error, Eq, PartialEq)]
+#[repr(u16)]
+#[error("{:?} ({})", self, strerror(*self as __wasi_errno_t))]
+pub enum WasiError {
+    ESUCCESS = __WASI_ERRNO_SUCCESS,
+    E2BIG = __WASI_ERRNO_2BIG,
+    EACCES = __WASI_ERRNO_ACCES,
+    EADDRINUSE = __WASI_ERRNO_ADDRINUSE,
+    EADDRNOTAVAIL = __WASI_ERRNO_ADDRNOTAVAIL,
+    EAFNOSUPPORT = __WASI_ERRNO_AFNOSUPPORT,
+    EAGAIN = __WASI_ERRNO_AGAIN,
+    EALREADY = __WASI_ERRNO_ALREADY,
+    EBADF = __WASI_ERRNO_BADF,
+    EBADMSG = __WASI_ERRNO_BADMSG,
+    EBUSY = __WASI_ERRNO_BUSY,
+    ECANCELED = __WASI_ERRNO_CANCELED,
+    ECHILD = __WASI_ERRNO_CHILD,
+    ECONNABORTED = __WASI_ERRNO_CONNABORTED,
+    ECONNREFUSED = __WASI_ERRNO_CONNREFUSED,
+    ECONNRESET = __WASI_ERRNO_CONNRESET,
+    EDEADLK = __WASI_ERRNO_DEADLK,
+    EDESTADDRREQ = __WASI_ERRNO_DESTADDRREQ,
+    EDOM = __WASI_ERRNO_DOM,
+    EDQUOT = __WASI_ERRNO_DQUOT,
+    EEXIST = __WASI_ERRNO_EXIST,
+    EFAULT = __WASI_ERRNO_FAULT,
+    EFBIG = __WASI_ERRNO_FBIG,
+    EHOSTUNREACH = __WASI_ERRNO_HOSTUNREACH,
+    EIDRM = __WASI_ERRNO_IDRM,
+    EILSEQ = __WASI_ERRNO_ILSEQ,
+    EINPROGRESS = __WASI_ERRNO_INPROGRESS,
+    EINTR = __WASI_ERRNO_INTR,
+    EINVAL = __WASI_ERRNO_INVAL,
+    EIO = __WASI_ERRNO_IO,
+    EISCONN = __WASI_ERRNO_ISCONN,
+    EISDIR = __WASI_ERRNO_ISDIR,
+    ELOOP = __WASI_ERRNO_LOOP,
+    EMFILE = __WASI_ERRNO_MFILE,
+    EMLINK = __WASI_ERRNO_MLINK,
+    EMSGSIZE = __WASI_ERRNO_MSGSIZE,
+    EMULTIHOP = __WASI_ERRNO_MULTIHOP,
+    ENAMETOOLONG = __WASI_ERRNO_NAMETOOLONG,
+    ENETDOWN = __WASI_ERRNO_NETDOWN,
+    ENETRESET = __WASI_ERRNO_NETRESET,
+    ENETUNREACH = __WASI_ERRNO_NETUNREACH,
+    ENFILE = __WASI_ERRNO_NFILE,
+    ENOBUFS = __WASI_ERRNO_NOBUFS,
+    ENODEV = __WASI_ERRNO_NODEV,
+    ENOENT = __WASI_ERRNO_NOENT,
+    ENOEXEC = __WASI_ERRNO_NOEXEC,
+    ENOLCK = __WASI_ERRNO_NOLCK,
+    ENOLINK = __WASI_ERRNO_NOLINK,
+    ENOMEM = __WASI_ERRNO_NOMEM,
+    ENOMSG = __WASI_ERRNO_NOMSG,
+    ENOPROTOOPT = __WASI_ERRNO_NOPROTOOPT,
+    ENOSPC = __WASI_ERRNO_NOSPC,
+    ENOSYS = __WASI_ERRNO_NOSYS,
+    ENOTCONN = __WASI_ERRNO_NOTCONN,
+    ENOTDIR = __WASI_ERRNO_NOTDIR,
+    ENOTEMPTY = __WASI_ERRNO_NOTEMPTY,
+    ENOTRECOVERABLE = __WASI_ERRNO_NOTRECOVERABLE,
+    ENOTSOCK = __WASI_ERRNO_NOTSOCK,
+    ENOTSUP = __WASI_ERRNO_NOTSUP,
+    ENOTTY = __WASI_ERRNO_NOTTY,
+    ENXIO = __WASI_ERRNO_NXIO,
+    EOVERFLOW = __WASI_ERRNO_OVERFLOW,
+    EOWNERDEAD = __WASI_ERRNO_OWNERDEAD,
+    EPERM = __WASI_ERRNO_PERM,
+    EPIPE = __WASI_ERRNO_PIPE,
+    EPROTO = __WASI_ERRNO_PROTO,
+    EPROTONOSUPPORT = __WASI_ERRNO_PROTONOSUPPORT,
+    EPROTOTYPE = __WASI_ERRNO_PROTOTYPE,
+    ERANGE = __WASI_ERRNO_RANGE,
+    EROFS = __WASI_ERRNO_ROFS,
+    ESPIPE = __WASI_ERRNO_SPIPE,
+    ESRCH = __WASI_ERRNO_SRCH,
+    ESTALE = __WASI_ERRNO_STALE,
+    ETIMEDOUT = __WASI_ERRNO_TIMEDOUT,
+    ETXTBSY = __WASI_ERRNO_TXTBSY,
+    EXDEV = __WASI_ERRNO_XDEV,
+    ENOTCAPABLE = __WASI_ERRNO_NOTCAPABLE,
+}
+
+impl WasiError {
+    pub fn as_raw_errno(self) -> __wasi_errno_t {
+        self as __wasi_errno_t
+    }
+}
+
+impl From<std::convert::Infallible> for WasiError {
+    fn from(_err: std::convert::Infallible) -> Self {
+        unreachable!()
+    }
+}
+
+impl From<std::num::TryFromIntError> for WasiError {
+    fn from(_err: std::num::TryFromIntError) -> Self {
+        Self::EOVERFLOW
+    }
+}
+
+impl From<std::str::Utf8Error> for WasiError {
+    fn from(_err: std::str::Utf8Error) -> Self {
+        Self::EILSEQ
+    }
+}
+
 pub(crate) const RIGHTS_ALL: __wasi_rights_t = __WASI_RIGHTS_FD_DATASYNC
     | __WASI_RIGHTS_FD_READ
     | __WASI_RIGHTS_FD_SEEK