Serialize undefined as null in collections, remove it in mappings

fix #571
fix #325

CHANGELOG.md

@@ -23,6 +23,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Line and column in exceptions are now formatted as `(X:Y)` instead of
   `at line X, column Y` (also present in compact format), #332.
 - Code snippet created in exceptions now contains multiple lines with line numbers.
+- `dump()` now serializes `undefined` as `null` in collections and removes keys with
+  `undefined` in mappings, #571.
+- `dump()` with `skipInvalid=true` now serializes invalid items in collections as null.
 
 ### Added
 - Added `.mjs` (es modules) support.

lib/dumper.js

@@ -565,9 +565,12 @@ function writeFlowSequence(state, level, object) {
       length;
 
   for (index = 0, length = object.length; index < length; index += 1) {
-    // Write only valid elements.
-    if (writeNode(state, level, object[index], false, false)) {
-      if (index !== 0) _result += ',' + (!state.condenseFlow ? ' ' : '');
+    // Write only valid elements, put null instead of invalid elements.
+    if (writeNode(state, level, object[index], false, false) ||
+        (typeof object[index] === 'undefined' &&
+         writeNode(state, level, null, false, false))) {
+
+      if (_result !== '') _result += ',' + (!state.condenseFlow ? ' ' : '');
       _result += state.dump;
     }
   }
@@ -583,9 +586,12 @@ function writeBlockSequence(state, level, object, compact) {
       length;
 
   for (index = 0, length = object.length; index < length; index += 1) {
-    // Write only valid elements.
-    if (writeNode(state, level + 1, object[index], true, true, false, true)) {
-      if (!compact || index !== 0) {
+    // Write only valid elements, put null instead of invalid elements.
+    if (writeNode(state, level + 1, object[index], true, true, false, true) ||
+        (typeof object[index] === 'undefined' &&
+         writeNode(state, level + 1, null, true, true, false, true))) {
+
+      if (!compact || _result !== '') {
         _result += generateNextLine(state, level);
       }
 
@@ -616,7 +622,7 @@ function writeFlowMapping(state, level, object) {
   for (index = 0, length = objectKeyList.length; index < length; index += 1) {
 
     pairBuffer = '';
-    if (index !== 0) pairBuffer += ', ';
+    if (_result !== '') pairBuffer += ', ';
 
     if (state.condenseFlow) pairBuffer += '"';
 
@@ -671,7 +677,7 @@ function writeBlockMapping(state, level, object, compact) {
   for (index = 0, length = objectKeyList.length; index < length; index += 1) {
     pairBuffer = '';
 
-    if (!compact || index !== 0) {
+    if (!compact || _result !== '') {
       pairBuffer += generateNextLine(state, level);
     }
 
@@ -823,6 +829,8 @@ function writeNode(state, level, object, block, compact, iskey, isblockseq) {
       if (state.tag !== '?') {
         writeScalar(state, state.dump, level, iskey, inblock);
       }
+    } else if (type === '[object Undefined]') {
+      return false;
     } else {
       if (state.skipInvalid) return false;
       throw new YAMLException('unacceptable kind of an object to dump ' + type);

test/issues/0571.js

@@ -0,0 +1,114 @@
+'use strict';
+
+
+const assert = require('assert');
+const yaml   = require('../../');
+
+
+describe('Undefined', function () {
+  let undef = new yaml.Type('!undefined', {
+    kind: 'scalar',
+    resolve: () => true,
+    construct: () => {},
+    predicate: object => typeof object === 'undefined',
+    represent: () => ''
+  });
+
+  let undef_schema = yaml.DEFAULT_SCHEMA.extend(undef);
+
+
+  it('Should replace undefined with null in collections', function () {
+    let str;
+
+    str = yaml.dump([ undefined, 1, undefined, null, 2 ], { flowLevel: 0 });
+    assert(str.match(/^\[/));
+    assert.deepStrictEqual(
+      yaml.load(str),
+      [ null, 1, null, null, 2 ]
+    );
+
+    str = yaml.dump([ undefined, 1, undefined, null, 2 ], { flowLevel: -1 });
+    assert(str.match(/^- /));
+    assert.deepStrictEqual(
+      yaml.load(str),
+      [ null, 1, null, null, 2 ]
+    );
+  });
+
+
+  it('Should remove keys with undefined in mappings', function () {
+    let str;
+
+    str = yaml.dump({ t: undefined, foo: 1, bar: undefined, baz: null }, { flowLevel: 0 });
+    assert(str.match(/^\{/));
+    assert.deepStrictEqual(
+      yaml.load(str),
+      { foo: 1, baz: null }
+    );
+
+    str = yaml.dump({ t: undefined, foo: 1, bar: undefined, baz: null }, { flowLevel: -1 });
+    assert(str.match(/^foo:/));
+    assert.deepStrictEqual(
+      yaml.load(str),
+      { foo: 1, baz: null }
+    );
+  });
+
+
+  it("Should serialize top-level undefined to ''", function () {
+    assert.strictEqual(yaml.dump(undefined), '');
+  });
+
+
+  it('Should serialize undefined if schema is available', function () {
+    assert.deepStrictEqual(
+      yaml.load(
+        yaml.dump([ 1, undefined, null, 2 ], { schema: undef_schema }),
+        { schema: undef_schema }
+      ),
+      [ 1, undefined, null, 2 ]
+    );
+
+    assert.deepStrictEqual(
+      yaml.load(
+        yaml.dump({ foo: 1, bar: undefined, baz: null }, { schema: undef_schema }),
+        { schema: undef_schema }
+      ),
+      { foo: 1, bar: undefined, baz: null }
+    );
+  });
+
+
+  it('Should respect null formatting', function () {
+    assert.strictEqual(
+      yaml.dump([ undefined ], { styles: { '!!null': 'uppercase' } }),
+      '- NULL\n'
+    );
+  });
+
+
+  it('Should return an error if neither null nor undefined schemas are available', function () {
+    assert.throws(() => {
+      yaml.dump([ 'foo', undefined, 'bar' ], { schema: yaml.FAILSAFE_SCHEMA });
+    }, /unacceptable kind of an object to dump/);
+  });
+
+
+  it('Should skip leading values correctly', function () {
+    assert.strictEqual(
+      yaml.dump([ () => {}, 'a' ], { flowLevel: 0, skipInvalid: true }),
+      '[a]\n');
+
+    assert.strictEqual(
+      yaml.dump([ () => {}, 'a' ], { flowLevel: -1, skipInvalid: true }),
+      '- a\n');
+
+    assert.strictEqual(
+      yaml.dump({ a: () => {}, b: 'a' }, { flowLevel: 0, skipInvalid: true }),
+      '{b: a}\n');
+
+    assert.strictEqual(
+      yaml.dump({ a: () => {}, b: 'a' }, { flowLevel: -1, skipInvalid: true }),
+      'b: a\n');
+  });
+});

test/units/skip-invalid.js

@@ -7,7 +7,6 @@ var yaml   = require('../../');
 
 var sample = {
   number: 42,
-  undef:  undefined,
   string: 'hello',
   func:   function (a, b) { return a + b; },
   regexp: /^hel+o/,