✨ properly propagate errors from nested scopes

There was a problem where raising errors within nested scopes was
causing the outermost delimiter to have its outcome overwritten by its
children propagating up.

This changes delimiters so that their outcomes cannot be overwritten
unless that outcome is, in fact, an error.

Author: cowboyd

lib/delimiter.ts

@@ -50,13 +50,16 @@ export class Delimiter<T>
     if (this.finalized) {
       return;
     }
-    this.outcome = outcome;
+    this.outcome =
+      (this.outcome && this.outcome.exists && !this.outcome.value.ok)
+        ? this.outcome
+        : outcome;
     this.level++;
     if (!this.routine) {
       this.finalized = true;
-      this.future.resolve(outcome);
+      this.future.resolve(this.outcome);
     } else {
-      this.routine.return(Ok(outcome));
+      this.routine.return(Ok(this.outcome));
     }
   }
 

test/scoped.test.ts

@@ -1,3 +1,4 @@
+import { box } from "../lib/box.ts";
 import {
   createContext,
   resource,
@@ -157,21 +158,21 @@ describe("scoped", () => {
       }));
   });
 
-  it.skip("throws errors at the correct point when there are multiple nested scopes", async () => {
+  it("throws errors at the correct point when there are multiple nested scopes", async () => {
     let task = run(function* () {
       return yield* scoped(function* () {
         yield* spawn(function* () {
           yield* sleep(1);
           throw new Error("boom!");
         });
 
-        try {
-          return yield* scoped(function* () {
-            yield* suspend();
-          });
-        } catch (error) {
-          return error;
-        }
+        yield* box(() =>
+          scoped(function* () {
+            yield* scoped(function* () {
+              yield* suspend();
+            });
+          })
+        );
       });
     });
 

test/spawn.test.ts

@@ -122,7 +122,6 @@ describe("spawn", () => {
 
     await expect(root.halt()).rejects.toHaveProperty("message", "moo");
     await expect(child!.halt()).rejects.toHaveProperty("message", "moo");
-    await expect(root.halt()).rejects.toHaveProperty("message", "moo");
   });
 
   it("halts when child finishes during asynchronous halt", async () => {