Use macro to implement our traits for `std` types

We want to implement the traits for more types which would be tedious
without a macro and it'd risk forgetting to forward some method since
they may be speialized. This also adds previously-forgotten
specializations. It also relaxes the implicit `Sized` bound on
`BufReader` and `BufWriter` in Rust versions above 1.72.

io/Cargo.toml

@@ -23,4 +23,4 @@ all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
 
 [lints.rust]
-unexpected_cfgs = { level = "deny" }
+unexpected_cfgs = { level = "deny", check-cfg = ['cfg(rust_v_1_72)'] }

io/build.rs

@@ -0,0 +1,37 @@
+fn main() {
+    let rustc = std::env::var_os("RUSTC");
+    let rustc = rustc.as_ref().map(std::path::Path::new).unwrap_or_else(|| "rustc".as_ref());
+    let output = std::process::Command::new(rustc)
+        .arg("--version")
+        .output()
+        .unwrap_or_else(|error| panic!("failed to run `{:?} --version`: {:?}", rustc, error));
+    assert!(output.status.success(), "{:?} -- version returned non-zero exit code", rustc);
+    let stdout = String::from_utf8(output.stdout).expect("rustc produced non-UTF-8 output");
+    let version_prefix = "rustc ";
+    if !stdout.starts_with(version_prefix) {
+        panic!("unexpected rustc output: {}", stdout);
+    }
+
+    let version = &stdout[version_prefix.len()..];
+    let end = version.find(&[' ', '-'] as &[_]).unwrap_or(version.len());
+    let version = &version[..end];
+    let mut version_components = version.split('.');
+    let major = version_components.next().unwrap();
+    assert_eq!(major, "1", "unexpected Rust major version");
+    let minor = version_components
+        .next()
+        .unwrap_or("0")
+        .parse::<u64>()
+        .expect("invalid Rust minor version");
+
+    let msrv = std::env::var("CARGO_PKG_RUST_VERSION").unwrap();
+    let mut msrv = msrv.split(".");
+    let msrv_major = msrv.next().unwrap();
+    assert_eq!(msrv_major, "1", "unexpected Rust major version");
+    let msrv_minor = msrv.next().unwrap().parse::<u64>().unwrap();
+
+    // print cfg for all interesting versions less than or equal to minor
+    for version in msrv_minor..=minor {
+        println!("cargo:rustc-cfg=rust_v_1_{}", version);
+    }
+}

io/src/bridge.rs

@@ -255,17 +255,73 @@ impl<T: super::Write> super::Write for ToStd<T> {
     }
 }
 
-impl<R: std::io::Read> super::Read for std::io::BufReader<R> {
-    #[inline]
-    fn read(&mut self, buf: &mut [u8]) -> super::Result<usize> { Ok(std::io::Read::read(self, buf)?) }
+macro_rules! impl_our {
+    (impl$(<$($gen:ident $(: $gent:path)?),*>)? Read for $std_type:ty $(where $($where:tt)*)?) => {
+        impl$(<$($gen$(: $gent)?),*>)? super::Read for $std_type $(where $($where)*)? {
+            #[inline]
+            fn read(&mut self, buf: &mut [u8]) -> super::Result<usize> {
+                std::io::Read::read(self, buf).map_err(Into::into)
+            }
+
+            #[inline]
+            fn read_exact(&mut self, buf: &mut [u8]) -> super::Result<()> {
+                std::io::Read::read_exact(self, buf).map_err(Into::into)
+            }
+        }
+    };
+
+    (impl$(<$($gen:ident $(: $gent:path)?),*>)? BufRead for $std_type:ty $(where $($where:tt)*)?) => {
+        impl$(<$($gen$(: $gent)?),*>)? super::BufRead for $std_type $(where $($where)*)? {
+            #[inline]
+            fn fill_buf(&mut self) -> super::Result<&[u8]> {
+                std::io::BufRead::fill_buf(self).map_err(Into::into)
+            }
+
+            #[inline]
+            fn consume(&mut self, amount: usize) {
+                std::io::BufRead::consume(self, amount)
+            }
+        }
+    };
+
+    (impl$(<$($gen:ident $(: $gent:path)?),*>)? Write for $std_type:ty $(where $($where:tt)*)?) => {
+        impl$(<$($gen$(: $gent)?),*>)? super::Write for $std_type $(where $($where)*)? {
+            #[inline]
+            fn write(&mut self, buf: &[u8]) -> super::Result<usize> {
+                std::io::Write::write(self, buf).map_err(Into::into)
+            }
+
+            #[inline]
+            fn flush(&mut self) -> super::Result<()> {
+                std::io::Write::flush(self).map_err(Into::into)
+            }
+
+            #[inline]
+            fn write_all(&mut self, buf: &[u8]) -> super::Result<()> {
+                std::io::Write::write_all(self, buf).map_err(Into::into)
+            }
+        }
+    };
 }
 
-impl<R: std::io::Read> super::BufRead for std::io::BufReader<R> {
-    #[inline]
-    fn fill_buf(&mut self) -> super::Result<&[u8]> { Ok(std::io::BufRead::fill_buf(self)?) }
+#[cfg(rust_v_1_72)]
+impl_our! {
+    impl<R: std::io::Read> Read for std::io::BufReader<R> where R: ?Sized
+}
 
-    #[inline]
-    fn consume(&mut self, amount: usize) { std::io::BufRead::consume(self, amount) }
+#[cfg(not(rust_v_1_72))]
+impl_our! {
+    impl<R: std::io::Read> Read for std::io::BufReader<R>
+}
+
+#[cfg(rust_v_1_72)]
+impl_our! {
+    impl<R: std::io::Read> BufRead for std::io::BufReader<R> where R: ?Sized
+}
+
+#[cfg(not(rust_v_1_72))]
+impl_our! {
+    impl<R: std::io::Read> BufRead for std::io::BufReader<R>
 }
 
 impl std::io::Write for super::Sink {
@@ -279,10 +335,12 @@ impl std::io::Write for super::Sink {
     fn flush(&mut self) -> std::io::Result<()> { Ok(()) }
 }
 
-impl<W: std::io::Write> super::Write for std::io::BufWriter<W> {
-    #[inline]
-    fn write(&mut self, buf: &[u8]) -> super::Result<usize> { Ok(std::io::Write::write(self, buf)?) }
-
-    #[inline]
-    fn flush(&mut self) -> super::Result<()> { Ok(std::io::Write::flush(self)?) }
+#[cfg(rust_v_1_72)]
+impl_our! {
+    impl<W: std::io::Write> Write for std::io::BufWriter<W> where W: ?Sized
+}
+
+#[cfg(not(rust_v_1_72))]
+impl_our! {
+    impl<W: std::io::Write> Write for std::io::BufWriter<W>
 }