Implement text serialization of strings

Use json.encode/json.decode.  This gets some strings wrong but it
should be enough to make more progress.

Testing with hardcoded strings is already getting awkward.

Change-Id: Ie0b168bec611ed93da13fff90f86232bb56c713f
Reviewed-on: https://dart-review.googlesource.com/c/87663
Reviewed-by: Daniel Hillerström <hillerstrom@google.com>
Commit-Queue: Kevin Millikin <kmillikin@google.com>

pkg/kernel/lib/text/serializer_combinators.dart

@@ -4,6 +4,8 @@
 
 library kernel.serializer_combinators;
 
+import 'dart:convert' show json;
+
 import '../ast.dart' show Expression;
 import 'text_serializer.dart' show ExpressionTagger;
 
@@ -28,7 +30,23 @@ class Nothing extends TextSerializer<void> {
   bool get isEmpty => true;
 }
 
-// == Serializer/deserializers for basic Dart types
+class DartString extends TextSerializer<String> {
+  const DartString();
+
+  String readFrom(Iterator<Object> stream) {
+    if (stream.current is! String) {
+      throw StateError("expected an atom, found a list");
+    }
+    String result = json.decode(stream.current);
+    stream.moveNext();
+    return result;
+  }
+
+  void writeTo(StringBuffer buffer, String object) {
+    buffer.write(json.encode(object));
+  }
+}
+
 class DartInt extends TextSerializer<int> {
   const DartInt();
 

pkg/kernel/lib/text/text_reader.dart

@@ -21,6 +21,8 @@ class TextIterator implements Iterator<Object /* String | TextIterator */ > {
   static int space = ' '.codeUnitAt(0);
   static int lparen = '('.codeUnitAt(0);
   static int rparen = ')'.codeUnitAt(0);
+  static int dquote = '"'.codeUnitAt(0);
+  static int bslash = '\\'.codeUnitAt(0);
 
   final String input;
   int index;
@@ -44,11 +46,33 @@ class TextIterator implements Iterator<Object /* String | TextIterator */ > {
   }
 
   void skipToEndOfAtom() {
+    bool isQuoted = false;
+    if (index < input.length && input.codeUnitAt(index) == dquote) {
+      ++index;
+      isQuoted = true;
+    }
     do {
       if (index >= input.length) return;
       int codeUnit = input.codeUnitAt(index);
-      if (codeUnit == space || codeUnit == rparen) return;
-      ++index;
+      if (isQuoted) {
+        // Terminator.
+        if (codeUnit == dquote) {
+          ++index;
+          return;
+        }
+        // Escaped double quote.
+        if (codeUnit == bslash &&
+            index < input.length + 1 &&
+            input.codeUnitAt(index + 1) == dquote) {
+          index += 2;
+        } else {
+          ++index;
+        }
+      } else {
+        // Terminator.
+        if (codeUnit == space || codeUnit == rparen) return;
+        ++index;
+      }
     } while (true);
   }
 

pkg/kernel/lib/text/text_serializer.dart

@@ -13,6 +13,7 @@ import '../visitor.dart' show ExpressionVisitor;
 class ExpressionTagger extends ExpressionVisitor<String> {
   const ExpressionTagger();
 
+  String visitStringLiteral(StringLiteral _) => "string";
   String visitIntLiteral(IntLiteral _) => "int";
   String visitDoubleLiteral(DoubleLiteral _) => "double";
   String visitBoolLiteral(BoolLiteral _) => "bool";
@@ -21,17 +22,26 @@ class ExpressionTagger extends ExpressionVisitor<String> {
 
 // ==== Serializers for BasicLiterals
 const TextSerializer<BasicLiteral> basicLiteralSerializer = Case([
+  "string",
   "int",
   "double",
   "bool",
   "null"
 ], [
+  stringLiteralSerializer,
   intLiteralSerializer,
   doubleLiteralSerializer,
   boolLiteralSerializer,
   nullLiteralSerializer
 ]);
 
+const TextSerializer<StringLiteral> stringLiteralSerializer =
+    Wrapped(unwrapStringLiteral, wrapStringLiteral, DartString());
+
+String unwrapStringLiteral(StringLiteral literal) => literal.value;
+
+StringLiteral wrapStringLiteral(String value) => new StringLiteral(value);
+
 const TextSerializer<IntLiteral> intLiteralSerializer =
     Wrapped(unwrapIntLiteral, wrapIntLiteral, DartInt());
 

pkg/kernel/test/text_serializer_test.dart

@@ -31,13 +31,17 @@ String writeBasicLiteral(BasicLiteral literal) {
 void test() {
   List<String> failures = [];
   List<String> tests = [
+    "(string \"Hello, 'string'!\")",
+    "(string \"Hello, \\\"string\\\"!\")",
+    "(string \"Yeah nah yeah, here is\\nthis really long string haiku\\n"
+        "blowing in the wind\\n\")",
     "(int 42)",
     "(int 0)",
     "(int -1001)",
     "(double 3.14159)",
     "(bool true)",
     "(bool false)",
-    "(null)"
+    "(null)",
   ];
   for (var test in tests) {
     var literal = readBasicLiteral(test);