Don't use .unwrap() or unimplemented in examples. (#748)

Panicking isn't super nice for people who are using the examples to learn
their way around.

Author: sunfishcode

examples/dup2_to_replace_stdio.rs

@@ -2,21 +2,21 @@
 //! file descriptors.
 
 #[cfg(all(not(windows), feature = "pipe", feature = "stdio"))]
-fn main() {
+fn main() -> std::io::Result<()> {
     use rustix::pipe::pipe;
     use rustix::stdio::{dup2_stdin, dup2_stdout};
     use std::io::{BufRead, BufReader};
 
     // Create some new file descriptors that we'll use to replace stdio's file
     // descriptors with.
-    let (reader, writer) = pipe().unwrap();
+    let (reader, writer) = pipe()?;
 
     // Use `dup2` to copy our new file descriptors over the stdio file descriptors.
     //
     // Rustix has a plain `dup2` function too, but it requires a `&mut OwnedFd`,
     // so these helper functions make it easier to use when replacing stdio fds.
-    dup2_stdin(&reader).unwrap();
-    dup2_stdout(&writer).unwrap();
+    dup2_stdin(&reader)?;
+    dup2_stdout(&writer)?;
 
     // We can also drop the original file descriptors now, since `dup2` creates
     // new file descriptors with independent lifetimes.
@@ -30,11 +30,13 @@ fn main() {
     // silly that we connected our stdout to our own stdin, but it's just an
     // example :-).
     let mut s = String::new();
-    BufReader::new(std::io::stdin()).read_line(&mut s).unwrap();
+    BufReader::new(std::io::stdin()).read_line(&mut s)?;
     assert_eq!(s, "hello, world!\n");
+
+    Ok(())
 }
 
 #[cfg(not(all(not(windows), feature = "pipe", feature = "stdio")))]
-fn main() {
-    unimplemented!()
+fn main() -> Result<(), &'static str> {
+    Err("This example requires --features=pipe,stdio and is not supported on Windows.")
 }

examples/hello.rs

@@ -34,6 +34,6 @@ fn main() -> std::io::Result<()> {
 }
 
 #[cfg(any(not(feature = "stdio"), not(feature = "std"), windows))]
-fn main() {
-    unimplemented!()
+fn main() -> Result<(), &'static str> {
+    Err("This example requires --features=stdio,std and is not supported on Windows.")
 }

examples/kq.rs

@@ -84,6 +84,6 @@ fn main() -> std::io::Result<()> {
 }
 
 #[cfg(not(all(bsd, feature = "event")))]
-fn main() {
-    unimplemented!()
+fn main() -> Result<(), &'static str> {
+    Err("This example requires --features=event and is only supported on BSD.")
 }

examples/process.rs

@@ -16,7 +16,7 @@ fn main() -> io::Result<()> {
     if let Some(ppid) = getppid() {
         println!(
             "Parent Group Pid: {}",
-            getpgid(Some(ppid)).unwrap().as_raw_nonzero()
+            getpgid(Some(ppid))?.as_raw_nonzero()
         );
     }
     println!("Uid: {}", getuid().as_raw());
@@ -91,6 +91,6 @@ fn main() -> io::Result<()> {
 }
 
 #[cfg(any(windows, not(all(feature = "process", feature = "param"))))]
-fn main() -> io::Result<()> {
-    unimplemented!()
+fn main() -> Result<(), &'static str> {
+    Err("This example requires --features=process,param and is not supported on Windows.")
 }

examples/stdio.rs

@@ -343,6 +343,6 @@ fn key(b: u8) -> String {
 }
 
 #[cfg(any(windows, not(feature = "stdio")))]
-fn main() {
-    unimplemented!()
+fn main() -> Result<(), &'static str> {
+    Err("This example requires --features=stdio and is not supported on Windows.")
 }

examples/termios.rs

@@ -44,6 +44,6 @@ fn main() -> std::io::Result<()> {
 }
 
 #[cfg(any(windows, not(feature = "termios")))]
-fn main() {
-    unimplemented!()
+fn main() -> Result<(), &'static str> {
+    Err("This example requires --features=termios and is not supported on Windows.")
 }

examples/time.rs

@@ -44,6 +44,6 @@ fn main() {
 }
 
 #[cfg(any(windows, target_os = "espidf", not(feature = "time")))]
-fn main() {
-    unimplemented!()
+fn main() -> Result<(), &'static str> {
+    Err("This example requires --features=time and is not supported on Windows or ESP-IDF.")
 }