[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/sys/unix/linux/host_impl.rs

@@ -1,11 +1,11 @@
-use crate::{wasi, Result};
+use crate::wasi::{self, WasiResult};
 
 pub(crate) const O_RSYNC: yanix::file::OFlag = yanix::file::OFlag::RSYNC;
 
-pub(crate) fn stdev_from_nix(dev: libc::dev_t) -> Result<wasi::__wasi_device_t> {
+pub(crate) fn stdev_from_nix(dev: libc::dev_t) -> WasiResult<wasi::__wasi_device_t> {
     Ok(wasi::__wasi_device_t::from(dev))
 }
 
-pub(crate) fn stino_from_nix(ino: libc::ino_t) -> Result<wasi::__wasi_inode_t> {
+pub(crate) fn stino_from_nix(ino: libc::ino_t) -> WasiResult<wasi::__wasi_inode_t> {
     Ok(wasi::__wasi_device_t::from(ino))
 }

crates/wasi-common/src/sys/unix/linux/hostcalls_impl.rs

@@ -1,9 +1,9 @@
 use crate::fdentry::Descriptor;
 use crate::hostcalls_impl::PathGet;
-use crate::Result;
+use crate::wasi::WasiResult;
 use std::os::unix::prelude::AsRawFd;
 
-pub(crate) fn path_unlink_file(resolved: PathGet) -> Result<()> {
+pub(crate) fn path_unlink_file(resolved: PathGet) -> WasiResult<()> {
     use yanix::file::{unlinkat, AtFlag};
     unsafe {
         unlinkat(
@@ -15,7 +15,7 @@ pub(crate) fn path_unlink_file(resolved: PathGet) -> Result<()> {
     .map_err(Into::into)
 }
 
-pub(crate) fn path_symlink(old_path: &str, resolved: PathGet) -> Result<()> {
+pub(crate) fn path_symlink(old_path: &str, resolved: PathGet) -> WasiResult<()> {
     use yanix::file::symlinkat;
 
     log::debug!("path_symlink old_path = {:?}", old_path);
@@ -25,7 +25,7 @@ pub(crate) fn path_symlink(old_path: &str, resolved: PathGet) -> Result<()> {
         .map_err(Into::into)
 }
 
-pub(crate) fn path_rename(resolved_old: PathGet, resolved_new: PathGet) -> Result<()> {
+pub(crate) fn path_rename(resolved_old: PathGet, resolved_new: PathGet) -> WasiResult<()> {
     use yanix::file::renameat;
     match (resolved_old.dirfd(), resolved_new.dirfd()) {
         (Descriptor::OsHandle(resolved_old_file), Descriptor::OsHandle(resolved_new_file)) => {
@@ -47,10 +47,10 @@ pub(crate) fn path_rename(resolved_old: PathGet, resolved_new: PathGet) -> Resul
 
 pub(crate) mod fd_readdir_impl {
     use crate::sys::fdentry_impl::OsHandle;
-    use crate::Result;
+    use crate::wasi::WasiResult;
     use yanix::dir::Dir;
 
-    pub(crate) fn get_dir_from_os_handle(os_handle: &mut OsHandle) -> Result<Box<Dir>> {
+    pub(crate) fn get_dir_from_os_handle(os_handle: &mut OsHandle) -> WasiResult<Box<Dir>> {
         // We need to duplicate the fd, because `opendir(3)`:
         //     After a successful call to fdopendir(), fd is used internally by the implementation,
         //     and should not otherwise be used by the application.