first pass at splitting out a test, making ctx/errno reusable

tests/ctx.rs

@@ -0,0 +1,34 @@
+use wiggle_runtime::GuestError;
+
+pub struct WasiCtx {
+    pub guest_errors: Vec<GuestError>,
+}
+
+impl WasiCtx {
+    pub fn new() -> Self {
+        Self {
+            guest_errors: vec![],
+        }
+    }
+}
+
+// Errno is used as a first return value in the functions above, therefore
+// it must implement GuestErrorType with type Context = WasiCtx.
+// The context type should let you do logging or debugging or whatever you need
+// with these errors. We just push them to vecs.
+#[macro_export]
+macro_rules! impl_errno {
+    ( $errno:ty ) => {
+        impl wiggle_runtime::GuestErrorType for $errno {
+            type Context = WasiCtx;
+            fn success() -> $errno {
+                <$errno>::Ok
+            }
+            fn from_error(e: GuestError, ctx: &mut WasiCtx) -> $errno {
+                eprintln!("GUEST ERROR: {:?}", e);
+                ctx.guest_errors.push(e);
+                types::Errno::InvalidArg
+            }
+        }
+    };
+}