Add ability to override quoting style for scalar values

README.md

@@ -183,6 +183,7 @@ options:
 - `noCompatMode` _(default: `false`)_ - if `true` don't try to be compatible with older
   yaml versions. Currently: don't quote "yes", "no" and so on, as required for YAML 1.1
 - `condenseFlow` _(default: `false`)_ - if `true` flow sequences will be condensed, omitting the space between `a, b`. Eg. `'[a,b]'`, and omitting the space between `key: value` and quoting the key. Eg. `'{"a":b}'` Can be useful when using yaml for pretty URL query params as spaces are %-encoded.
+- `scalarQuoteStyle` _(default: `null`)_ set the quote style for scalar values. Valid values are `"single"` and `"double"`. Double quoted values will not be changed to single quotes.
 
 The following table show availlable styles (e.g. "canonical",
 "binary"...) available for each tag (.e.g. !!null, !!int ...). Yaml

lib/js-yaml/dumper.js

@@ -105,16 +105,17 @@ function encodeHex(character) {
 }
 
 function State(options) {
-  this.schema       = options['schema'] || DEFAULT_FULL_SCHEMA;
-  this.indent       = Math.max(1, (options['indent'] || 2));
-  this.skipInvalid  = options['skipInvalid'] || false;
-  this.flowLevel    = (common.isNothing(options['flowLevel']) ? -1 : options['flowLevel']);
-  this.styleMap     = compileStyleMap(this.schema, options['styles'] || null);
-  this.sortKeys     = options['sortKeys'] || false;
-  this.lineWidth    = options['lineWidth'] || 80;
-  this.noRefs       = options['noRefs'] || false;
-  this.noCompatMode = options['noCompatMode'] || false;
-  this.condenseFlow = options['condenseFlow'] || false;
+  this.schema           = options['schema'] || DEFAULT_FULL_SCHEMA;
+  this.indent           = Math.max(1, (options['indent'] || 2));
+  this.skipInvalid      = options['skipInvalid'] || false;
+  this.flowLevel        = (common.isNothing(options['flowLevel']) ? -1 : options['flowLevel']);
+  this.styleMap         = compileStyleMap(this.schema, options['styles'] || null);
+  this.sortKeys         = options['sortKeys'] || false;
+  this.lineWidth        = options['lineWidth'] || 80;
+  this.noRefs           = options['noRefs'] || false;
+  this.noCompatMode     = options['noCompatMode'] || false;
+  this.condenseFlow     = options['condenseFlow'] || false;
+  this.scalarQuoteStyle = options['scalarQuoteStyle'] || null;
 
   this.implicitTypes = this.schema.compiledImplicit;
   this.explicitTypes = this.schema.compiledExplicit;
@@ -246,6 +247,9 @@ var STYLE_PLAIN   = 1,
     STYLE_FOLDED  = 4,
     STYLE_DOUBLE  = 5;
 
+var SCALAR_QUOTE_STYLE_SINGLE = 'single',
+    SCALAR_QUOTE_STYLE_DOUBLE = 'double';
+
 // Determines which scalar styles are possible and returns the preferred style.
 // lineWidth = -1 => no limit.
 // Pre-conditions: str.length > 0.
@@ -324,6 +328,9 @@ function chooseScalarStyle(string, singleLineOnly, indentPerLevel, lineWidth, te
 function writeScalar(state, string, level, iskey) {
   state.dump = (function () {
     if (string.length === 0) {
+      if (state.scalarQuoteStyle === SCALAR_QUOTE_STYLE_DOUBLE) {
+        return '""';
+      }
       return "''";
     }
     if (!state.noCompatMode &&
@@ -350,7 +357,17 @@ function writeScalar(state, string, level, iskey) {
       return testImplicitResolving(state, string);
     }
 
-    switch (chooseScalarStyle(string, singleLineOnly, state.indent, lineWidth, testAmbiguity)) {
+    var scalarStyle = chooseScalarStyle(string, singleLineOnly, state.indent, lineWidth, testAmbiguity);
+
+    if (iskey !== true && (scalarStyle === STYLE_PLAIN || scalarStyle === STYLE_SINGLE)) {
+      if (state.scalarQuoteStyle === SCALAR_QUOTE_STYLE_SINGLE) {
+        scalarStyle = STYLE_SINGLE;
+      } else if (state.scalarQuoteStyle === SCALAR_QUOTE_STYLE_DOUBLE) {
+        scalarStyle = STYLE_DOUBLE;
+      }
+    }
+
+    switch (scalarStyle) {
       case STYLE_PLAIN:
         return string;
       case STYLE_SINGLE:

test/20-dumper.js

@@ -28,4 +28,15 @@ suite('Dumper', function () {
       }
     });
   });
+
+  test('single quote scalars', function () {
+    var serialized = yaml.dump({ k: 'v', empty: '' }, { schema: TEST_SCHEMA, scalarQuoteStyle: 'single' });
+    assert.equal(serialized, "k: 'v'\nempty: ''\n");
+  });
+
+  test('double quote scalars', function () {
+    var serialized = yaml.dump({ k: 'v', empty: '' }, { schema: TEST_SCHEMA, scalarQuoteStyle: 'double' });
+    assert.equal(serialized, 'k: "v"\nempty: ""\n');
+  });
+
 });