Add support for selectordinal arguments

This adds support for parsing `selectordinal` arguments, which have
similar semantics to `plural` arguments but use ordinal pluralization.

Relates to: formatjs/intl-messageformat#84
See: formatjs/intl-messageformat#84 (comment)

src/parser.pegjs

@@ -67,6 +67,7 @@ argumentElement
 elementFormat
     = simpleFormat
     / pluralFormat
+    / selectOrdinalFormat
     / selectFormat
 
 simpleFormat
@@ -78,11 +79,22 @@ simpleFormat
     }
 
 pluralFormat
-    = 'plural' _ ',' _ offset:offset? _ options:optionalFormatPattern+ {
+    = 'plural' _ ',' _ pluralStyle:pluralStyle {
         return {
-            type   : 'pluralFormat',
-            offset : offset || 0,
-            options: options
+            type   : pluralStyle.type,
+            ordinal: false,
+            offset : pluralStyle.offset || 0,
+            options: pluralStyle.options
+        };
+    }
+
+selectOrdinalFormat
+    = 'selectordinal' _ ',' _ pluralStyle:pluralStyle {
+        return {
+            type   : pluralStyle.type,
+            ordinal: true,
+            offset : pluralStyle.offset || 0,
+            options: pluralStyle.options
         }
     }
 
@@ -91,7 +103,7 @@ selectFormat
         return {
             type   : 'selectFormat',
             options: options
-        }
+        };
     }
 
 selector
@@ -112,6 +124,15 @@ offset
         return number;
     }
 
+pluralStyle
+    = offset:offset? _ options:optionalFormatPattern+ {
+        return {
+            type   : 'pluralFormat',
+            offset : offset,
+            options: options
+        };
+    }
+
 // -- Helpers ------------------------------------------------------------------
 
 ws 'whitespace' = [ \t\n\r]+

test/unit/parser.js

@@ -173,6 +173,76 @@ describe('parse()', function () {
         });
     });
 
+    describe('parse("{floor, selectordinal, =0{ground} one{#st} two{#nd} few{#rd} other{#th}} floor")', function () {
+        var msg = '{floor, selectordinal, =0{ground} one{#st} two{#nd} few{#rd} other{#th}} floor';
+        var ast = parse(msg);
+
+        it('should contain 2 `elements`', function () {
+            expect(ast.elements).to.have.length(2);
+        });
+
+        it('should contain an `argumentElement`', function () {
+            var element = ast.elements[0];
+            expect(element).to.be.an('object');
+            expect(element).to.have.property('type');
+            expect(element.type).to.equal('argumentElement');
+            expect(element).to.have.property('id');
+            expect(element.id).to.equal('floor');
+            expect(element).to.have.property('format');
+
+            var format = element.format;
+            expect(format).to.be.an('object');
+            expect(format).to.have.property('type');
+            expect(format.type).to.equal('pluralFormat');
+            expect(format).to.have.property('offset');
+            expect(format.offset).to.equal(0);
+            expect(format.ordinal).to.equal(true);
+        });
+
+        it('should contain 5 `options`', function () {
+            var options = ast.elements[0].format.options;
+            expect(options).to.have.length(5);
+
+            var option = options[0];
+            expect(option).to.be.an('object');
+            expect(option).to.have.property('type');
+            expect(option.type).to.equal('optionalFormatPattern');
+            expect(option).to.have.property('selector');
+            expect(option.selector).to.equal('=0');
+            expect(option).to.have.property('value');
+            expect(option.value).to.be.an('object');
+
+            expect(options[1].selector).to.equal('one');
+            expect(options[2].selector).to.equal('two');
+            expect(options[3].selector).to.equal('few');
+            expect(options[4].selector).to.equal('other');
+        });
+
+        it('should contain nested `messageFormatPattern` values for each option', function () {
+            var options = ast.elements[0].format.options;
+
+            var value = options[0].value;
+            expect(value).to.have.property('type');
+            expect(value.type).to.equal('messageFormatPattern');
+            expect(value).to.have.property('elements');
+            expect(value.elements).to.be.an('array');
+            expect(value.elements).to.have.length(1);
+
+            var element = value.elements[0];
+            expect(element).to.be.an('object');
+            expect(element).to.have.property('type');
+            expect(element.type).to.equal('messageTextElement');
+            expect(element).to.have.property('value');
+            expect(element.value).to.equal('ground');
+
+            expect(options[0].value.elements[0].value).to.equal('ground');
+            expect(options[1].value.elements[0].value).to.equal('#st');
+            expect(options[2].value.elements[0].value).to.equal('#nd');
+            expect(options[3].value.elements[0].value).to.equal('#rd');
+            expect(options[4].value.elements[0].value).to.equal('#th');
+        });
+    });
+
     describe('parse("{gender, select, female {woman} male {man} other {person}}")', function () {
         var msg = '{gender, select, female {woman} male {man} other {person}}';
         var ast = parse(msg);