feat: Add an option for reporting duplicate object keys as an error

Author: prantlf

.vscode/launch.json

@@ -19,7 +19,7 @@
       "type": "node",
       "request": "launch",
       "name": "test",
-      "program": "${workspaceRoot}/test/parse1.js",
+      "program": "${workspaceRoot}/test/parse2.js",
       "args": [
         "--native-parser"
       ],

README.md

@@ -15,7 +15,7 @@ This is a fork of the original package with the following enhancements:
 * Walks directories recursively (by Paul Vollmer).
 * Provides 100% compatible interface to the native `JSON.parse` method.
 * Optionally recognizes JavaScript-style comments and single quoted strings.
-* Optionally ignores trailing commas in objects and arrays.
+* Optionally ignores trailing commas and reports duplicate object keys as an error.
 * Supports [JSON Schema] drafts 04, 06 and 07.
 * Prefers the native JSON parser to gain the [best performance], while showing error messages of the same quality.
 * Implements JavaScript modules using [UMD] to work everywhere.
@@ -81,6 +81,7 @@ By default, `jsonlint` will either report a syntax error with details or pretty-
       -C, --comments               recognize and ignore JavaScript-style comments
       -S, --single-quoted-strings  support single quotes as string delimiters
       -T, --trailing-commas'       ignore trailing commas in objects and arrays
+      -D, --no-duplicate-keys      report duplicate object keys as an error
       -V, --validate [file]        JSON schema file to use for validation
       -e, --environment [env]      which specification of JSON Schema
                                    the validation file uses
@@ -132,6 +133,7 @@ The `parse` method offers more detailed [error information](#error-handling), th
 | `ignoreComments`           | ignores single-line and multi-line JavaScript-style comments during parsing as another "whitespace" (boolean) |
 | `ignoreTrailingCommas`     | ignores trailing commas in objects and arrays (boolean) |
 | `allowSingleQuotedStrings` | accepts strings delimited by single-quotes too (boolean) |
+| `allowDuplicateObjectKeys` | allows reporting duplicate object keys as an error (boolean) |
 | `mode`                     | sets multiple options according to the type of input data (string) |
 
 The `mode` parameter (string) sets parsing options to match a common format of input data:

lib/cli.js

@@ -25,6 +25,7 @@ var options = require('commander')
   .option('-C, --comments', 'recognize and ignore JavaScript-style comments')
   .option('-S, --single-quoted-strings', 'support single quotes as string delimiters')
   .option('-T, --trailing-commas', 'ignore trailing commas in objects and arrays')
+  .option('-D, --no-duplicate-keys', 'report duplicate object keys as an error')
   .option('-V, --validate [file]', 'JSON schema file to use for validation')
   .option('-e, --environment [env]', 'which specification of JSON Schema the validation file uses')
   .option('-q, --quiet', 'do not print the parsed json to stdin')
@@ -56,7 +57,8 @@ function parse (source, file) {
       mode: options.mode,
       ignoreComments: options.comments,
       ignoreTrailingCommas: options.trailingCommas,
-      allowSingleQuotedStrings: options.singleQuotedStrings
+      allowSingleQuotedStrings: options.singleQuotedStrings,
+      allowDuplicateObjectKeys: options.duplicateKeys
     }
     parsed = parser.parse(source, parserOptions)
     if (options.sortKeys) {

lib/validator.js

@@ -57,7 +57,8 @@
         mode: options.mode,
         ignoreComments: options.ignoreComments,
         ignoreTrailingCommas: options.ignoreTrailingCommas,
-        allowSingleQuotedStrings: options.allowSingleQuotedStrings
+        allowSingleQuotedStrings: options.allowSingleQuotedStrings,
+        allowDuplicateObjectKeys: options.allowDuplicateObjectKeys
       })
       validate = ajv.compile(schema)
     } catch (error) {

src/configurable-parser.js

@@ -22,6 +22,10 @@ function processOptions (options) {
       changed.allowSingleQuotedStrings = this.allowSingleQuotedStrings
       this.allowSingleQuotedStrings = options.allowSingleQuotedStrings
     }
+    if (options.allowDuplicateObjectKeys !== undefined) {
+      changed.allowDuplicateObjectKeys = this.allowDuplicateObjectKeys
+      this.allowDuplicateObjectKeys = options.allowDuplicateObjectKeys
+    }
     if (options.mode !== undefined) {
       changed.mode = this.mode
       this.mode = options.mode
@@ -47,9 +51,9 @@ var isSafari = typeof navigator !== 'undefined' && /Safari/.test(navigator.userA
 var oldNode = typeof process !== 'undefined' && process.version.startsWith('v4.')
 
 function needsCustomParser () {
-  return this.ignoreComments || this.allowSingleQuotedStrings ||
-    this.ignoreTrailingCommas || this.mode === 'cjson' || this.mode === 'json5' ||
-    isSafari || oldNode
+  return this.ignoreComments || this.ignoreTrailingCommas ||
+    this.allowSingleQuotedStrings || this.allowDuplicateObjectKeys === false ||
+    this.mode === 'cjson' || this.mode === 'json5' || isSafari || oldNode
 }
 
 function getReviver (options) {

src/custom-parser.js

@@ -46,6 +46,7 @@ function parseCustom (input, options) { // eslint-disable-line no-unused-vars
   var ignoreComments = options.ignoreComments || options.mode === 'cjson' || json5
   var ignoreTrailingCommas = options.ignoreTrailingCommas || json5
   var allowSingleQuotedStrings = options.allowSingleQuotedStrings || json5
+  var allowDuplicateObjectKeys = options.allowDuplicateObjectKeys
   var reviver = options.reviver
 
   var isLineTerminator = json5 ? Uni.isLineTerminator : Uni.isLineTerminatorJSON
@@ -227,6 +228,9 @@ function parseCustom (input, options) { // eslint-disable-line no-unused-vars
     while (position < inputLength) {
       skipWhiteSpace()
       var key = parseKey()
+      if (allowDuplicateObjectKeys === false && result[key]) {
+        fail('Duplicate key: ' + key)
+      }
       skipWhiteSpace()
 
       var char = input[position++]

test/parse2.js

@@ -152,6 +152,11 @@ addTest('[1,\r\n2,\r3,\n]')
 
 assert.throws(parse.bind(null, '{-1:42}', { mode: 'json5' }))
 
+assert.deepEqual(parse('{ "key": 1, "key": 2}'), { key: 2 })
+assert.throws(function () {
+  parse('{ "key": 1, "key": 2}', { allowDuplicateObjectKeys: false })
+})
+
 for (i = 0; i < 100; ++i) {
   var str = '-01.e'.split('')
 

web/jsonlint.html

@@ -104,6 +104,10 @@ <h1>JSON Lint</h1>
             <input type="checkbox" id="single-quoted-strings">
             <label for="single-quoted-strings">Recognize single-quoted strings</label>
           </div>
+          <div>
+            <input type="checkbox" checked id="duplicate-object-keys">
+            <label for="single-quoted-strings">Allow duplicate object keys</label>
+          </div>
           <div>
             <input type="checkbox" id="with-schema">
             <label for="with-schema">Use schema</label>
@@ -144,7 +148,8 @@ <h2>Result</h2>
           var parserOptions = {
             ignoreComments: document.getElementById('comments').checked,
             ignoreTrailingCommas: document.getElementById('trailing-commas').checked,
-            allowSingleQuotedStrings: document.getElementById('single-quoted-strings').checked
+            allowSingleQuotedStrings: document.getElementById('single-quoted-strings').checked,
+            allowDuplicateObjectKeys: document.getElementById('duplicate-object-keys').checked,
           }
           var parsed = parser.parse(document.getElementById('data').value, parserOptions)
           if (document.getElementById('with-schema').checked) {