feat(js): add EszipError type

This commit adds a new error type that is returned from the JS API. It
has fields to describe the location (specifier + line + col) of an
error, in addition to storing the error message.

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+  "deno.enable": true
+}

lib/Cargo.toml

@@ -21,3 +21,4 @@ wasm-bindgen-futures = { version = "0.4.28" }
 tokio = { version = "1.16", features = ["io-std", "io-util"] }
 console_error_panic_hook = "0.1.7"
 anyhow = "1"
+serde = { version = "1.0.145", features = ["derive"] }

lib/eszip_test.ts

@@ -1,8 +1,9 @@
-import { build, Parser } from "./mod.ts";
+import { build, EszipError, Parser } from "./mod.ts";
 import {
   assert,
   assertEquals,
-} from "https://deno.land/std@0.123.0/testing/asserts.ts";
+  assertRejects,
+} from "https://deno.land/std@0.155.0/testing/asserts.ts";
 
 Deno.test("roundtrip build + parse", async () => {
   const eszip = await build([
@@ -47,3 +48,18 @@ Deno.test("build default loader", async () => {
   const eszip = await build(["https://deno.land/std@0.123.0/fs/mod.ts"]);
   assert(eszip instanceof Uint8Array);
 });
+
+Deno.test("eszip error", async () => {
+  const err = await assertRejects(
+    () => build(["file:///does/not/exist.ts"]),
+    EszipError,
+  );
+  assertEquals(
+    err.specifier,
+    "file:///does/not/exist.ts",
+  );
+  assertEquals(
+    err.message,
+    "Module not found.",
+  );
+});