fix(cli): give context when failed to load import map (#10478)

cli/ops/runtime_compiler.rs

@@ -87,7 +87,13 @@ async fn op_emit(
       let file = program_state
         .file_fetcher
         .fetch(&import_map_specifier, &mut runtime_permissions)
-        .await?;
+        .await
+        .map_err(|e| {
+          generic_error(format!(
+            "Unable to load '{}' import map: {}",
+            import_map_specifier, e
+          ))
+        })?;
       ImportMap::from_json(import_map_specifier.as_str(), &file.source)?
     };
     Some(import_map)

cli/program_state.rs

@@ -101,7 +101,11 @@ impl ProgramState {
             )?;
           let file = file_fetcher
             .fetch(&import_map_specifier, &mut Permissions::allow_all())
-            .await?;
+            .await
+            .context(format!(
+              "Unable to load '{}' import map",
+              import_map_specifier
+            ))?;
           let import_map =
             ImportMap::from_json(import_map_specifier.as_str(), &file.source)?;
           Some(import_map)

cli/tests/compiler_api_test.ts

@@ -338,3 +338,22 @@ Deno.test({
     assert(files["deno:///bundle.js"].endsWith("})();\n"));
   },
 });
+
+Deno.test({
+  name: `Deno.emit() - throws descriptive error when unable to load import map`,
+  async fn() {
+    await assertThrowsAsync(
+      async () => {
+        await Deno.emit("/a.ts", {
+          bundle: "classic",
+          sources: {
+            "/a.ts": `console.log("hello");`,
+          },
+          importMapPath: "file:///import_map_does_not_exist.json",
+        });
+      },
+      Error,
+      "Unable to load 'file:///import_map_does_not_exist.json' import map",
+    );
+  },
+});

cli/tests/error_import_map_unable_to_load.out

@@ -0,0 +1,4 @@
+error: Unable to load '[WILDCARD]' import map
+
+Caused by:
+    [WILDCARD]

cli/tests/integration_tests.rs

@@ -3841,6 +3841,17 @@ console.log("finish");
     http_server: true,
   });
 
+  // This test ensures that a descriptive error is shown when we're unable to load
+  // the import map. Even though this tests only the `run` subcommand, we can be sure
+  // that the error message is similar for other subcommands as they all use
+  // `program_state.maybe_import_map` to access the import map underneath.
+  itest!(error_import_map_unable_to_load {
+    args:
+      "run --import-map=import_maps/does_not_exist.json import_maps/test.ts",
+    output: "error_import_map_unable_to_load.out",
+    exit_code: 1,
+  });
+
   #[test]
   fn no_validate_asm() {
     let output = util::deno_cmd()