wasix: Improve SpawnError::Other

Use Box<dyn Error> instead of a string.

Also adds an AnyhowStdError wrapper to allow converting an anyhow::Error to a
Box<dyn Error>.

Needed for better error handling/propagation.

lib/wasix/src/lib.rs

@@ -172,7 +172,7 @@ pub enum SpawnError {
     #[error("runtime error")]
     Runtime(#[from] WasiRuntimeError),
     #[error("{0}")]
-    Other(String),
+    Other(#[from] Box<dyn std::error::Error + Send + Sync>),
 }
 
 impl SpawnError {
@@ -222,6 +222,33 @@ impl WasiRuntimeError {
     }
 }
 
+/// Wrapper for [`anyhow::Error`] that implements [`std::error::Error`].
+pub struct AnyhowStdError(pub anyhow::Error);
+
+impl std::fmt::Debug for AnyhowStdError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+impl std::fmt::Display for AnyhowStdError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+impl std::error::Error for AnyhowStdError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        Some(&*self.0)
+    }
+}
+
+impl From<anyhow::Error> for AnyhowStdError {
+    fn from(error: anyhow::Error) -> Self {
+        Self(error)
+    }
+}
+
 #[allow(clippy::result_large_err)]
 pub(crate) fn run_wasi_func(
     func: &wasmer::Function,

lib/wasix/src/os/console/mod.rs

@@ -218,7 +218,7 @@ impl Console {
             .with_capabilities(self.capabilities.clone())
             .prepare_webc_env(prog, &wasi_opts, &pkg, self.runtime.clone(), Some(root_fs))
             // TODO: better error conversion
-            .map_err(|err| SpawnError::Other(err.to_string()))?;
+            .map_err(|err| SpawnError::Other(Box::new(crate::AnyhowStdError(err))))?;
 
         // TODO: no unwrap!
         let env = builder