run-examples: Provide more error context for debugging

Use `anyhow` for nice errors and provide error context on commands that we run.

Cargo.lock

@@ -1742,6 +1742,7 @@ dependencies = [
 name = "run-examples"
 version = "0.18.0"
 dependencies = [
+ "anyhow",
  "cc",
 ]
 

crates/misc/run-examples/Cargo.toml

@@ -6,4 +6,5 @@ edition = "2018"
 publish = false
 
 [dependencies]
+anyhow = "1.0.31"
 cc = "1.0"

crates/misc/run-examples/src/main.rs

@@ -1,26 +1,25 @@
+use anyhow::Context;
 use std::collections::BTreeSet;
 use std::process::Command;
 
-fn main() {
+fn main() -> anyhow::Result<()> {
     let example_to_run = std::env::args().nth(1);
-    let examples = std::fs::read_dir("examples").unwrap();
-    let examples = examples
-        .filter_map(|e| {
-            let e = e.unwrap();
-            let path = e.path();
-            let dir = e.metadata().unwrap().is_dir();
-            if let Some("wat") = path.extension().and_then(|s| s.to_str()) {
-                return None;
-            }
+    let mut examples = BTreeSet::new();
+    for e in std::fs::read_dir("examples")? {
+        let e = e?;
+        let path = e.path();
+        let dir = e.metadata()?.is_dir();
+        if let Some("wat") = path.extension().and_then(|s| s.to_str()) {
+            continue;
+        }
 
-            Some((path.file_stem().unwrap().to_str().unwrap().to_owned(), dir))
-        })
-        .collect::<BTreeSet<_>>();
+        examples.insert((path.file_stem().unwrap().to_str().unwrap().to_owned(), dir));
+    }
 
     println!("======== Building libwasmtime.a ===========");
     run(Command::new("cargo")
         .args(&["build"])
-        .current_dir("crates/c-api"));
+        .current_dir("crates/c-api"))?;
 
     for (example, is_dir) in examples {
         if example == "README" {
@@ -43,13 +42,13 @@ fn main() {
                 .arg("-p")
                 .arg(format!("example-{}-wasm", example))
                 .arg("--target")
-                .arg(target));
+                .arg(target))?;
         }
         println!("======== Rust example `{}` ============", example);
         run(Command::new("cargo")
             .arg("run")
             .arg("--example")
-            .arg(&example));
+            .arg(&example))?;
 
         println!("======== C/C++ example `{}` ============", example);
         for extension in ["c", "cc"].iter() {
@@ -93,18 +92,22 @@ fn main() {
             if cfg!(target_os = "linux") {
                 cmd.arg("-lpthread").arg("-ldl").arg("-lm");
             }
-            run(&mut cmd);
+            run(&mut cmd)?;
 
-            run(&mut Command::new(exe));
+            run(&mut Command::new(exe))?;
         }
     }
+
+    Ok(())
 }
 
-fn run(cmd: &mut Command) {
-    let s = cmd.status().unwrap();
-    if !s.success() {
-        eprintln!("failed to run {:?}", cmd);
-        eprintln!("status: {}", s);
-        std::process::exit(1);
-    }
+fn run(cmd: &mut Command) -> anyhow::Result<()> {
+    (|| -> anyhow::Result<()> {
+        let s = cmd.status()?;
+        if !s.success() {
+            anyhow::bail!("Exited with failure status: {}", s);
+        }
+        Ok(())
+    })()
+    .with_context(|| format!("failed to run `{:?}`", cmd))
 }