Rollup merge of #114194 - thomcc:flushinline, r=cuviper

Inline trivial (noop) flush calls

At work I noticed that `writer.flush()?` didn't get optimized away in cases where the flush is obviously a no-op, which I had expected (well, desired).

I went through and added `#[inline]` to a bunch of cases that were obviously noops, or delegated to ones that were obviously noops. I omitted platforms I don't have access to (some tier3). I didn't do this very scientifically, in cases where it was non-obvious I left `#[inline]` off.

library/std/src/fs.rs

@@ -791,6 +791,7 @@ fn is_write_vectored(&self) -> bool {
         self.inner.is_write_vectored()
     }
 
+    #[inline]
     fn flush(&mut self) -> io::Result<()> {
         self.inner.flush()
     }
@@ -836,6 +837,7 @@ fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
     fn is_write_vectored(&self) -> bool {
         (&&*self).is_write_vectored()
     }
+    #[inline]
     fn flush(&mut self) -> io::Result<()> {
         (&*self).flush()
     }
@@ -881,6 +883,7 @@ fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
     fn is_write_vectored(&self) -> bool {
         (&**self).is_write_vectored()
     }
+    #[inline]
     fn flush(&mut self) -> io::Result<()> {
         (&**self).flush()
     }

library/std/src/io/readbuf.rs

@@ -310,6 +310,7 @@ fn write(&mut self, buf: &[u8]) -> Result<usize> {
         Ok(buf.len())
     }
 
+    #[inline]
     fn flush(&mut self) -> Result<()> {
         Ok(())
     }

library/std/src/net/tcp.rs

@@ -647,6 +647,7 @@ fn is_write_vectored(&self) -> bool {
         self.0.is_write_vectored()
     }
 
+    #[inline]
     fn flush(&mut self) -> io::Result<()> {
         Ok(())
     }
@@ -685,6 +686,7 @@ fn is_write_vectored(&self) -> bool {
         self.0.is_write_vectored()
     }
 
+    #[inline]
     fn flush(&mut self) -> io::Result<()> {
         Ok(())
     }

library/std/src/os/unix/net/stream.rs

@@ -712,6 +712,7 @@ fn is_write_vectored(&self) -> bool {
         self.0.is_write_vectored()
     }
 
+    #[inline]
     fn flush(&mut self) -> io::Result<()> {
         Ok(())
     }

library/std/src/process.rs

@@ -280,6 +280,7 @@ fn is_write_vectored(&self) -> bool {
         io::Write::is_write_vectored(&&*self)
     }
 
+    #[inline]
     fn flush(&mut self) -> io::Result<()> {
         (&*self).flush()
     }
@@ -299,6 +300,7 @@ fn is_write_vectored(&self) -> bool {
         self.inner.is_write_vectored()
     }
 
+    #[inline]
     fn flush(&mut self) -> io::Result<()> {
         Ok(())
     }

library/std/src/sys/hermit/fs.rs

@@ -335,6 +335,7 @@ pub fn is_write_vectored(&self) -> bool {
         false
     }
 
+    #[inline]
     pub fn flush(&self) -> io::Result<()> {
         Ok(())
     }

library/std/src/sys/unix/fs.rs

@@ -1204,6 +1204,7 @@ pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result
         self.0.write_vectored_at(bufs, offset)
     }
 
+    #[inline]
     pub fn flush(&self) -> io::Result<()> {
         Ok(())
     }

library/std/src/sys/unix/stdio.rs

@@ -54,6 +54,7 @@ fn is_write_vectored(&self) -> bool {
         true
     }
 
+    #[inline]
     fn flush(&mut self) -> io::Result<()> {
         Ok(())
     }
@@ -81,6 +82,7 @@ fn is_write_vectored(&self) -> bool {
         true
     }
 
+    #[inline]
     fn flush(&mut self) -> io::Result<()> {
         Ok(())
     }