Add JsonLiteral.asConst, updated CHANGELOG

Fix edge cases with String encoding in JsonLiteral generator
And add tests

Author: kevmoo

CHANGELOG.md

@@ -1,6 +1,8 @@
 ## 0.2.2
 
 * Enable support for `enum` values.
+* Added `asConst` to `JsonLiteral`.
+* Improved the handling of Dart-specific characters in JSON strings.
 
 ## 0.2.1
 

analysis_options.yaml

@@ -35,7 +35,6 @@ linter:
     - only_throw_errors
     - prefer_final_fields
     - prefer_is_not_empty
-    # Waiting for linter 0.1.33 to land in SDK
-    #- prefer_single_quotes
+    - prefer_single_quotes
     - slash_for_doc_comments
     - type_init_formals

example/example.g.dart

@@ -2,9 +2,14 @@
 // 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.
 
-// TODO: option to make the literal a const
 class JsonLiteral {
+  /// The relative path from the Dart file with the annotation to the file
+  /// containing the source JSON.
   final String path;
 
-  const JsonLiteral(this.path);
+  /// `true` if the JSON literal should be written as a constant.
+  final bool asConst;
+
+  const JsonLiteral(this.path, {bool asConst: false})
+      : this.asConst = asConst ?? false;
 }

lib/src/json_literal.dart

@@ -28,14 +28,89 @@ class JsonLiteralGenerator extends GeneratorForAnnotation<JsonLiteral> {
         p.join(sourcePathDir, annotation.read('path').stringValue));
     var content = JSON.decode(await buildStep.readAsString(fileId));
 
-    var thing = JSON.encode(content);
+    var asConst = annotation.read('asConst').boolValue;
 
-    var marked = _isConstType(content) ? 'const' : 'final';
+    var thing = _jsonLiteralAsDart(content, asConst).toString();
+    var marked = asConst ? 'const' : 'final';
 
     return '$marked _\$${element.displayName}JsonLiteral = $thing;';
   }
 }
 
-bool _isConstType(value) {
-  return value == null || value is String || value is num || value is bool;
+/// Returns a [String] representing a valid Dart literal for [value].
+///
+/// If [asConst] is `true`, the returned [String] is encoded as a `const`
+/// literal.
+String _jsonLiteralAsDart(dynamic value, bool asConst) {
+  if (value == null) return 'null';
+
+  if (value is String) return _jsonStringAsDart(value);
+
+  if (value is bool || value is num) return value.toString();
+
+  if (value is List) {
+    var listItems =
+        value.map((v) => _jsonLiteralAsDart(v, asConst)).join(',\n');
+    return '${asConst ? 'const' : ''}[$listItems]';
+  }
+
+  if (value is Map) return _jsonMapAsDart(value, asConst);
+
+  throw new StateError(
+      'Should never get here – with ${value.runtimeType} - `$value`.');
+}
+
+String _jsonMapAsDart(Map value, bool asConst) {
+  var buffer = new StringBuffer();
+  if (asConst) {
+    buffer.write('const ');
+  }
+  buffer.write('{');
+
+  var first = true;
+  value.forEach((String k, v) {
+    if (first) {
+      first = false;
+    } else {
+      buffer.writeln(',');
+    }
+    buffer.write(_jsonStringAsDart(k));
+    buffer.write(':');
+    buffer.write(_jsonLiteralAsDart(v, asConst));
+  });
+
+  buffer.write('}');
+
+  return buffer.toString();
+}
+
+String _jsonStringAsDart(String value) {
+  var containsSingleQuote = value.contains("'");
+  var contains$ = value.contains(r'$');
+
+  if (containsSingleQuote) {
+    if (value.contains('"')) {
+      // `value` contains both single and double quotes as well as `$`.
+      // The only safe way to wrap the content is to escape all of the
+      // problematic characters.
+      var string = value
+          .replaceAll('\$', '\\\$')
+          .replaceAll('"', '\\"')
+          .replaceAll("'", "\\'");
+      return "'$string'";
+    } else if (contains$) {
+      // `value` contains "'" and "$", but not '"'.
+      // Safely wrap it in a raw string within double-quotes.
+      return 'r"$value"';
+    }
+    return '"$value"';
+  } else if (contains$) {
+    // `value` contains "$", but no "'"
+    // wrap it in a raw string using single quotes
+    return "r'$value'";
+  }
+
+  // `value` contains no problematic characters - except for '"' maybe.
+  // Wrap it in standard single-quotes.
+  return "'$value'";
 }

lib/src/json_literal_generator.dart

@@ -0,0 +1,24 @@
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:test/test.dart';
+import 'package:path/path.dart' as p;
+
+import 'test_files/json_literal.dart';
+import 'test_utils.dart';
+
+main() {
+  test('literal round-trip', () {
+    var dataFilePath =
+        p.join(getPackagePath(), 'test', 'test_files', 'data.json');
+    var dataFile = new File(dataFilePath);
+
+    var dataString = loudEncode(JSON.decode(dataFile.readAsStringSync()));
+    // FYI: nice to re-write the test data when it's changed to keep it pretty
+    // ... but not a good idea to ship this
+    // dataFile.writeAsStringSync(dataString);
+    var dartString = loudEncode(data);
+
+    expect(dartString, dataString);
+  });
+}

test/json_literal_test.dart

@@ -0,0 +1,27 @@
+[
+ "simple string",
+ "'string with single quotes'",
+ "\"string with double quotes\"",
+ "'With singles and \"doubles\"'",
+ "dollar $igns",
+ "'single quotes and dollor $ig$'",
+ "${'nice!'}",
+ "\"\"hello\"\"",
+ "\"\"$double quotes and dollar signs\"\"",
+ "$scary with 'single quotes' and triple-doubles \"\"\"oh no!",
+ null,
+ true,
+ false,
+ 5,
+ 5.5351,
+ -5.5,
+ {},
+ {
+  "null": null,
+  "int": 42,
+  "double": 42.0,
+  "string": "string",
+  "list": [],
+  "bool": true
+ }
+]

test/test_files/data.json

@@ -0,0 +1,14 @@
+// Copyright (c) 2017, 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.
+
+library json_serializable.example;
+
+import 'package:json_serializable/annotations.dart';
+part 'json_literal.g.dart';
+
+@JsonLiteral('data.json')
+List get data => _$dataJsonLiteral;
+
+@JsonLiteral('data.json', asConst: true)
+List get asConst => _$asConstJsonLiteral;

test/test_files/json_literal.dart

@@ -88,7 +88,7 @@ void roundTripObject(object, factory(Map<String, dynamic> json)) {
 /// Prints out nested causes before throwing `JsonUnsupportedObjectError`.
 String loudEncode(object) {
   try {
-    return const JsonEncoder.withIndent(' ').convert(object.toJson());
+    return const JsonEncoder.withIndent(' ').convert(object);
   } on JsonUnsupportedObjectError catch (e) {
     var error = e;
     do {