Add str-based os_str implementation for wasm

On `wasm` the only legal way to construct an OS string is from a UTF-8
string. Every other platform publicly guarantees (through some
extension trait) either arbitrary bytes or (transcoded) UTF-16.

Therefore `wasm` can base its OS strings on UTF-8 strings. The
implementation is largely copied from the `unix` implementation, but
without the validation and with slightly more liberal use of
`#[inline]`.

An immediate benefit is that conversion back to UTF-8 strings is
free. But the motivation is that we want the `unix` implementation to
express that it can be sliced at arbitrary points, and this would be
inappropriate for `wasm` since it lacks an extension trait.

library/std/src/sys/unsupported/mod.rs

@@ -11,7 +11,6 @@ pub mod locks;
 pub mod net;
 pub mod once;
 pub mod os;
-#[path = "../unix/os_str.rs"]
 pub mod os_str;
 #[path = "../unix/path.rs"]
 pub mod path;

library/std/src/sys/unsupported/os_str.rs

@@ -0,0 +1,275 @@
+//! The underlying OsString/OsStr implementation on platforms where there isn't
+//! any particular OS encoding: just a `String`/`str`.
+
+use crate::borrow::Cow;
+use crate::collections::TryReserveError;
+use crate::fmt;
+use crate::mem;
+use crate::rc::Rc;
+use crate::str;
+use crate::string::String;
+use crate::sync::Arc;
+use crate::sys_common::{AsInner, FromInner, IntoInner};
+
+#[derive(Hash)]
+#[repr(transparent)]
+pub struct Buf {
+    pub inner: String,
+}
+
+#[repr(transparent)]
+pub struct Slice {
+    pub inner: str,
+}
+
+impl fmt::Debug for Slice {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&self.inner, formatter)
+    }
+}
+
+impl fmt::Display for Slice {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.inner, formatter)
+    }
+}
+
+impl fmt::Debug for Buf {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(self.as_slice(), formatter)
+    }
+}
+
+impl fmt::Display for Buf {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self.as_slice(), formatter)
+    }
+}
+
+impl Clone for Buf {
+    #[inline]
+    fn clone(&self) -> Self {
+        Buf { inner: self.inner.clone() }
+    }
+
+    #[inline]
+    fn clone_from(&mut self, source: &Self) {
+        self.inner.clone_from(&source.inner)
+    }
+}
+
+impl IntoInner<String> for Buf {
+    fn into_inner(self) -> String {
+        self.inner
+    }
+}
+
+impl FromInner<String> for Buf {
+    fn from_inner(inner: String) -> Self {
+        Buf { inner }
+    }
+}
+
+impl AsInner<str> for Buf {
+    #[inline]
+    fn as_inner(&self) -> &str {
+        &self.inner
+    }
+}
+
+impl Buf {
+    #[inline]
+    pub fn into_encoded_bytes(self) -> Vec<u8> {
+        self.inner.into_bytes()
+    }
+
+    #[inline]
+    pub unsafe fn from_encoded_bytes_unchecked(s: Vec<u8>) -> Self {
+        Self { inner: unsafe { String::from_utf8_unchecked(s) } }
+    }
+
+    #[inline]
+    pub fn from_string(s: String) -> Buf {
+        Buf { inner: s }
+    }
+
+    #[inline]
+    pub fn with_capacity(capacity: usize) -> Buf {
+        Buf { inner: String::with_capacity(capacity) }
+    }
+
+    #[inline]
+    pub fn clear(&mut self) {
+        self.inner.clear()
+    }
+
+    #[inline]
+    pub fn capacity(&self) -> usize {
+        self.inner.capacity()
+    }
+
+    #[inline]
+    pub fn reserve(&mut self, additional: usize) {
+        self.inner.reserve(additional)
+    }
+
+    #[inline]
+    pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
+        self.inner.try_reserve(additional)
+    }
+
+    #[inline]
+    pub fn reserve_exact(&mut self, additional: usize) {
+        self.inner.reserve_exact(additional)
+    }
+
+    #[inline]
+    pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
+        self.inner.try_reserve_exact(additional)
+    }
+
+    #[inline]
+    pub fn shrink_to_fit(&mut self) {
+        self.inner.shrink_to_fit()
+    }
+
+    #[inline]
+    pub fn shrink_to(&mut self, min_capacity: usize) {
+        self.inner.shrink_to(min_capacity)
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &Slice {
+        // SAFETY: Slice just wraps str,
+        // and &*self.inner is &str, therefore
+        // transmuting &str to &Slice is safe.
+        unsafe { mem::transmute(&*self.inner) }
+    }
+
+    #[inline]
+    pub fn as_mut_slice(&mut self) -> &mut Slice {
+        // SAFETY: Slice just wraps str,
+        // and &mut *self.inner is &mut str, therefore
+        // transmuting &mut str to &mut Slice is safe.
+        unsafe { mem::transmute(&mut *self.inner) }
+    }
+
+    #[inline]
+    pub fn into_string(self) -> Result<String, Buf> {
+        Ok(self.inner)
+    }
+
+    #[inline]
+    pub fn push_slice(&mut self, s: &Slice) {
+        self.inner.push_str(&s.inner)
+    }
+
+    #[inline]
+    pub fn into_box(self) -> Box<Slice> {
+        unsafe { mem::transmute(self.inner.into_boxed_str()) }
+    }
+
+    #[inline]
+    pub fn from_box(boxed: Box<Slice>) -> Buf {
+        let inner: Box<str> = unsafe { mem::transmute(boxed) };
+        Buf { inner: inner.into_string() }
+    }
+
+    #[inline]
+    pub fn into_arc(&self) -> Arc<Slice> {
+        self.as_slice().into_arc()
+    }
+
+    #[inline]
+    pub fn into_rc(&self) -> Rc<Slice> {
+        self.as_slice().into_rc()
+    }
+}
+
+impl Slice {
+    #[inline]
+    pub fn as_encoded_bytes(&self) -> &[u8] {
+        self.inner.as_bytes()
+    }
+
+    #[inline]
+    pub unsafe fn from_encoded_bytes_unchecked(s: &[u8]) -> &Slice {
+        unsafe { mem::transmute(s) }
+    }
+
+    #[inline]
+    pub fn from_str(s: &str) -> &Slice {
+        unsafe { mem::transmute(s) }
+    }
+
+    #[inline]
+    pub fn to_str(&self) -> Result<&str, crate::str::Utf8Error> {
+        Ok(&self.inner)
+    }
+
+    #[inline]
+    pub fn to_string_lossy(&self) -> Cow<'_, str> {
+        Cow::Borrowed(&self.inner)
+    }
+
+    pub fn to_owned(&self) -> Buf {
+        Buf { inner: self.inner.to_owned() }
+    }
+
+    pub fn clone_into(&self, buf: &mut Buf) {
+        self.inner.clone_into(&mut buf.inner)
+    }
+
+    #[inline]
+    pub fn into_box(&self) -> Box<Slice> {
+        let boxed: Box<str> = self.inner.into();
+        unsafe { mem::transmute(boxed) }
+    }
+
+    pub fn empty_box() -> Box<Slice> {
+        let boxed: Box<str> = Default::default();
+        unsafe { mem::transmute(boxed) }
+    }
+
+    #[inline]
+    pub fn into_arc(&self) -> Arc<Slice> {
+        let arc: Arc<str> = Arc::from(&self.inner);
+        unsafe { Arc::from_raw(Arc::into_raw(arc) as *const Slice) }
+    }
+
+    #[inline]
+    pub fn into_rc(&self) -> Rc<Slice> {
+        let rc: Rc<str> = Rc::from(&self.inner);
+        unsafe { Rc::from_raw(Rc::into_raw(rc) as *const Slice) }
+    }
+
+    #[inline]
+    pub fn make_ascii_lowercase(&mut self) {
+        self.inner.make_ascii_lowercase()
+    }
+
+    #[inline]
+    pub fn make_ascii_uppercase(&mut self) {
+        self.inner.make_ascii_uppercase()
+    }
+
+    #[inline]
+    pub fn to_ascii_lowercase(&self) -> Buf {
+        Buf { inner: self.inner.to_ascii_lowercase() }
+    }
+
+    #[inline]
+    pub fn to_ascii_uppercase(&self) -> Buf {
+        Buf { inner: self.inner.to_ascii_uppercase() }
+    }
+
+    #[inline]
+    pub fn is_ascii(&self) -> bool {
+        self.inner.is_ascii()
+    }
+
+    #[inline]
+    pub fn eq_ignore_ascii_case(&self, other: &Self) -> bool {
+        self.inner.eq_ignore_ascii_case(&other.inner)
+    }
+}

library/std/src/sys/wasm/mod.rs

@@ -8,7 +8,7 @@
 //! wide/production use yet, it's still all in the experimental category. This
 //! will likely change over time.
 //!
-//! Currently all functions here are basically stubs that immediately return
+//! Currently most functions here are basically stubs that immediately return
 //! errors. The hope is that with a portability lint we can turn actually just
 //! remove all this and just omit parts of the standard library if we're
 //! compiling for wasm. That way it's a compile time error for something that's
@@ -30,7 +30,7 @@ pub mod io;
 pub mod net;
 #[path = "../unsupported/os.rs"]
 pub mod os;
-#[path = "../unix/os_str.rs"]
+#[path = "../unsupported/os_str.rs"]
 pub mod os_str;
 #[path = "../unix/path.rs"]
 pub mod path;