fix: add explanatory error loading jsr specifier

src/mod.test.ts

@@ -4,11 +4,11 @@ import {
   ResolutionMode,
   Workspace,
 } from "./mod.ts";
-import { assert, assertEquals } from "@std/assert";
+import { assert, assertEquals, assertRejects } from "@std/assert";
 
 Deno.test("should resolve, load and get graph", async () => {
   const workspace = new Workspace({
-    nodeConditions: undefined, // unsure doesn't error
+    nodeConditions: undefined, // ensure doesn't error
   });
   const modFileUrl = import.meta.resolve("./mod.ts");
   const loader = await workspace.createLoader({
@@ -47,3 +47,21 @@ Deno.test("should resolve, load and get graph", async () => {
     assertEquals(loadResponse.specifier, "node:events");
   }
 });
+
+Deno.test("resolving a jsr specifier should fail with explanatory message", async () => {
+  const workspace = new Workspace({});
+  const modFileUrl = import.meta.resolve("./mod.ts");
+  const loader = await workspace.createLoader({
+    entrypoints: [modFileUrl],
+  });
+  assertRejects(
+    async () => {
+      await loader.load(
+        "jsr:@scope/version",
+        RequestedModuleType.Default,
+      );
+    },
+    Error,
+    "Failed loading 'jsr:@scope/version'. jsr: specifiers must be resolved to an https: specifier before being loaded.",
+  );
+});

src/rs_lib/lib.rs

@@ -467,7 +467,7 @@ impl DenoLoader {
         maintain_npm_specifiers: false,
       },
     )?;
-    Ok(resolved.to_string())
+    Ok(resolved.into())
   }
 
   pub async fn load(
@@ -502,6 +502,11 @@ impl DenoLoader {
 
     if url.scheme() == "node" {
       return Ok(create_external_repsonse(&url));
+    } else if url.scheme() == "jsr" {
+      bail!(
+        "Failed loading '{}'. jsr: specifiers must be resolved to an https: specifier before being loaded.",
+        url
+      );
     }
 
     match self