(Some) DiagnosticMessages can be serialized to/from json.

This is needed to serialize and deserialize problems to dill and
re-issuing problems as needed.

Change-Id: Id22d1c86f43b1b08c5e5a4d133869075e9b0c100
Reviewed-on: https://dart-review.googlesource.com/c/91743
Commit-Queue: Jens Johansen <jensj@google.com>
Reviewed-by: Peter von der Ahé <ahe@google.com>

pkg/front_end/lib/src/api_prototype/diagnostic_message.dart

@@ -4,7 +4,8 @@
 
 library front_end.diagnostic_message;
 
-import '../fasta/fasta_codes.dart' show Code, FormattedMessage;
+import '../fasta/fasta_codes.dart'
+    show Code, DiagnosticMessageFromJson, FormattedMessage;
 
 import '../fasta/severity.dart' show Severity;
 
@@ -38,7 +39,9 @@ abstract class DiagnosticMessage {
 
 /// This method is subject to change.
 Uri getMessageUri(DiagnosticMessage message) {
-  return message is FormattedMessage ? message.uri : null;
+  return message is FormattedMessage
+      ? message.uri
+      : message is DiagnosticMessageFromJson ? message.uri : null;
 }
 
 /// This method is subject to change.

pkg/front_end/lib/src/base/processed_options.dart

@@ -212,14 +212,17 @@ class ProcessedOptions {
     if (CompilerContext.current.options.setExitCodeOnProblem) {
       exitCode = 1;
     }
-    (_raw.onDiagnostic ??
-        _defaultDiagnosticMessageHandler)(format(message, severity, context));
+    reportDiagnosticMessage(format(message, severity, context));
     if (command_line_reporting.shouldThrowOn(severity)) {
       throw new DebugAbort(
           message.uri, message.charOffset, severity, StackTrace.current);
     }
   }
 
+  void reportDiagnosticMessage(DiagnosticMessage message) {
+    (_raw.onDiagnostic ?? _defaultDiagnosticMessageHandler)(message);
+  }
+
   void _defaultDiagnosticMessageHandler(DiagnosticMessage message) {
     printDiagnosticMessage(message, print);
   }

pkg/front_end/lib/src/fasta/fasta_codes.dart

@@ -4,7 +4,7 @@
 
 library fasta.codes;
 
-import 'dart:convert' show JsonEncoder;
+import 'dart:convert' show JsonEncoder, json;
 
 import 'package:kernel/ast.dart'
     show Constant, DartType, demangleMixinApplicationName;
@@ -185,10 +185,56 @@ class FormattedMessage implements DiagnosticMessage {
   }
 
   Map<String, Object> toJson() {
-    // The should be kept in sync with package:kernel/problems.md
+    // This should be kept in sync with package:kernel/problems.md
     return <String, Object>{
       "ansiFormatted": ansiFormatted.toList(),
       "plainTextFormatted": plainTextFormatted.toList(),
+      "severity": severity.index,
+      "uri": uri.toString(),
+    };
+  }
+
+  String toJsonString() {
+    JsonEncoder encoder = new JsonEncoder.withIndent("  ");
+    return encoder.convert(this);
+  }
+}
+
+class DiagnosticMessageFromJson implements DiagnosticMessage {
+  @override
+  final Iterable<String> ansiFormatted;
+
+  @override
+  final Iterable<String> plainTextFormatted;
+
+  @override
+  final Severity severity;
+
+  final Uri uri;
+
+  DiagnosticMessageFromJson(
+      this.ansiFormatted, this.plainTextFormatted, this.severity, this.uri);
+
+  factory DiagnosticMessageFromJson.fromJson(String jsonString) {
+    Map<String, Object> decoded = json.decode(jsonString);
+    List<String> ansiFormatted =
+        new List<String>.from(decoded["ansiFormatted"]);
+    List<String> plainTextFormatted =
+        new List<String>.from(decoded["plainTextFormatted"]);
+    Severity severity = Severity.values[decoded["severity"]];
+    Uri uri = Uri.parse(decoded["uri"]);
+
+    return new DiagnosticMessageFromJson(
+        ansiFormatted, plainTextFormatted, severity, uri);
+  }
+
+  Map<String, Object> toJson() {
+    // This should be kept in sync with package:kernel/problems.md
+    return <String, Object>{
+      "ansiFormatted": ansiFormatted.toList(),
+      "plainTextFormatted": plainTextFormatted.toList(),
+      "severity": severity.index,
+      "uri": uri.toString(),
     };
   }
 

pkg/front_end/test/messages_json_test.dart

@@ -0,0 +1,69 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:front_end/src/api_prototype/diagnostic_message.dart'
+    show DiagnosticMessage, getMessageUri;
+
+import 'package:front_end/src/fasta/fasta_codes.dart'
+    show DiagnosticMessageFromJson, FormattedMessage, LocatedMessage;
+
+import 'package:front_end/src/fasta/severity.dart' show Severity;
+
+/// Test that turning a message into json and back again retains the wanted
+/// information.
+main() {
+  for (int i = 0; i < Severity.values.length; i++) {
+    Severity severity = Severity.values[i];
+    LocatedMessage locatedMessage1 =
+        new LocatedMessage(Uri.parse("what:ever/fun_1.dart"), 117, 2, null);
+    FormattedMessage formattedMessage2 = new FormattedMessage(
+        null, "Formatted string #2", 13, 2, Severity.error, []);
+    FormattedMessage formattedMessage3 = new FormattedMessage(
+        null, "Formatted string #3", 313, 32, Severity.error, []);
+
+    FormattedMessage formattedMessage1 = new FormattedMessage(
+        locatedMessage1,
+        "Formatted string",
+        42,
+        86,
+        severity,
+        [formattedMessage2, formattedMessage3]);
+
+    DiagnosticMessageFromJson diagnosticMessageFromJson =
+        new DiagnosticMessageFromJson.fromJson(
+            formattedMessage1.toJsonString());
+    compareMessages(formattedMessage1, diagnosticMessageFromJson);
+
+    DiagnosticMessageFromJson diagnosticMessageFromJson2 =
+        new DiagnosticMessageFromJson.fromJson(
+            diagnosticMessageFromJson.toJsonString());
+    compareMessages(diagnosticMessageFromJson, diagnosticMessageFromJson2);
+
+    expect(diagnosticMessageFromJson2.toJsonString(),
+        formattedMessage1.toJsonString());
+  }
+}
+
+void compareMessages(DiagnosticMessage a, DiagnosticMessage b) {
+  List<String> list1 = a.ansiFormatted.toList();
+  List<String> list2 = b.ansiFormatted.toList();
+  expect(list1.length, list2.length);
+  for (int i = 0; i < list1.length; i++) {
+    expect(list1[i], list2[i]);
+  }
+
+  list1 = a.plainTextFormatted.toList();
+  list2 = b.plainTextFormatted.toList();
+  expect(list1.length, list2.length);
+  for (int i = 0; i < list1.length; i++) {
+    expect(list1[i], list2[i]);
+  }
+
+  expect(a.severity, b.severity);
+  expect(getMessageUri(a), getMessageUri(b));
+}
+
+void expect(Object actual, Object expect) {
+  if (expect != actual) throw "Expected $expect got $actual";
+}

pkg/front_end/test/severity_index_test.dart

@@ -0,0 +1,23 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:front_end/src/fasta/severity.dart' show Severity;
+
+/// Test that Severity has the expected indexes. Note that this is important
+/// and shouldn't be changed lightly because we use it in serialization!
+main() {
+  expect(Severity.context.index, 0);
+  expect(Severity.error.index, 1);
+  expect(Severity.internalProblem.index, 4);
+  expect(Severity.warning.index, 5);
+
+  expect(Severity.values[0], Severity.context);
+  expect(Severity.values[1], Severity.error);
+  expect(Severity.values[4], Severity.internalProblem);
+  expect(Severity.values[5], Severity.warning);
+}
+
+void expect(Object actual, Object expect) {
+  if (expect != actual) throw "Expected $expect got $actual";
+}

pkg/kernel/problems.md

@@ -10,9 +10,15 @@ Each string in the list is a json object consisting of these keys and values:
 
 `ansiFormatted`: A list of strings the contain ansi formatted (for instance with
 colors) problem-texts as reported by the compiler.
+
 `plainTextFormatted`: A list of strings that contain formatted plaintext
 problem-texts as reported by the compiler.
 
+`severity`: An integer representing severity. This should match the index in
+`package:front_end/src/fasta/severity.dart`.
+
+`uri: A uri that this problems relates to.
+
 These values are subject to change, but this file will be updated along with any
 such changes. On the code-side these are defined in
 `package:front_end/src/fasta/fasta_codes.dart`.