Allow ImporterResponse.result to be null (#59)

Author: nex3

CHANGELOG.md

@@ -1,9 +1,12 @@
 ## 1.0.0-beta.15
 
-* Support version 1.0.0-beta.16 of the Sass embedded protocol:
+* Support version 1.0.0-beta.17 of the Sass embedded protocol:
+
   * Treat invalid host function signatures as function errors rather than
     protocol errors.
 
+  * Allow `ImportResponse.result` to be null.
+
 ## 1.0.0-beta.14
 
 * Support `FileImporter`s.

lib/src/importer/host.dart

@@ -44,7 +44,7 @@ class HostImporter extends ImporterBase {
     }());
   }
 
-  sass.ImporterResult load(Uri url) {
+  sass.ImporterResult? load(Uri url) {
     return waitFor(() async {
       var response =
           await dispatcher.sendImportRequest(OutboundMessage_ImportRequest()
@@ -65,7 +65,7 @@ class HostImporter extends ImporterBase {
           throw response.error;
 
         case InboundMessage_ImportResponse_Result.notSet:
-          sendAndThrow(mandatoryError("ImportResponse.result"));
+          return null;
       }
     }());
   }

test/importer_test.dart

@@ -217,21 +217,6 @@ void main() {
 
   group("importing", () {
     group("emits a protocol error", () {
-      test("for an unset import result", () async {
-        process.inbound.add(compileString("@import 'other'", importers: [
-          InboundMessage_CompileRequest_Importer()..importerId = 1
-        ]));
-        await _canonicalize(process);
-
-        var import = getImportRequest(await process.outbound.next);
-        process.inbound.add(InboundMessage()
-          ..importResponse = (InboundMessage_ImportResponse()..id = import.id));
-
-        await _expectImportParamsError(
-            process, "Missing mandatory field ImportResponse.result");
-        await process.kill();
-      });
-
       test("for an import result with a relative sourceMapUrl", () async {
         process.inbound.add(compileString("@import 'other'", importers: [
           InboundMessage_CompileRequest_Importer()..importerId = 1
@@ -289,6 +274,29 @@ void main() {
       });
     });
 
+    test("null results count as not found", () async {
+      process.inbound.add(compileString("@import 'other'", importers: [
+        InboundMessage_CompileRequest_Importer()..importerId = 1
+      ]));
+
+      var canonicalizeRequest =
+          getCanonicalizeRequest(await process.outbound.next);
+      process.inbound.add(InboundMessage()
+        ..canonicalizeResponse = (InboundMessage_CanonicalizeResponse()
+          ..id = canonicalizeRequest.id
+          ..url = "o:other"));
+
+      var importRequest = getImportRequest(await process.outbound.next);
+      process.inbound.add(InboundMessage()
+        ..importResponse =
+            (InboundMessage_ImportResponse()..id = importRequest.id));
+
+      var failure = getCompileFailure(await process.outbound.next);
+      expect(failure.message, equals("Can't find stylesheet to import."));
+      expect(failure.span.text, equals("'other'"));
+      await process.kill();
+    });
+
     test("errors cause compilation to fail", () async {
       process.inbound.add(compileString("@import 'other'", importers: [
         InboundMessage_CompileRequest_Importer()..importerId = 1