[New] add getSymbolDescription and getInferredName helpers

helpers/getInferredName.js

@@ -0,0 +1,10 @@
+'use strict';
+
+var getInferredName;
+try {
+	// eslint-disable-next-line no-new-func
+	getInferredName = Function('s', 'return { [s]() {} }[s].name;');
+} catch (e) {}
+
+var inferred = function () {};
+module.exports = getInferredName && inferred.name === 'inferred' ? getInferredName : null;

helpers/getSymbolDescription.js

@@ -0,0 +1,30 @@
+'use strict';
+
+var GetIntrinsic = require('../GetIntrinsic');
+
+var callBound = require('./callBound');
+
+var $SyntaxError = GetIntrinsic('%SyntaxError%');
+var symToStr = callBound('Symbol.prototype.toString', true);
+
+var getInferredName = require('./getInferredName');
+
+module.exports = function getSymbolDescription(symbol) {
+	if (!symToStr) {
+		throw new $SyntaxError('Symbols are not supported in this environment');
+	}
+	var str = symToStr(symbol); // will throw if not a symbol
+
+	if (getInferredName) {
+		var name = getInferredName(symbol);
+		if (name === '') { return; }
+		// eslint-disable-next-line consistent-return
+		return name.slice(1, -1); // name.slice('['.length, -']'.length);
+	}
+
+	var desc = str.slice(7, -1); // str.slice('Symbol('.length, -')'.length);
+	if (desc) {
+		// eslint-disable-next-line consistent-return
+		return desc;
+	}
+};

test/helpers/getSymbolDescription.js

@@ -0,0 +1,50 @@
+'use strict';
+
+var test = require('tape');
+var debug = require('object-inspect');
+var forEach = require('foreach');
+
+var v = require('./values');
+var getSymbolDescription = require('../../helpers/getSymbolDescription');
+
+test('getSymbolDescription', function (t) {
+	t.test('no symbols', { skip: v.hasSymbols }, function (st) {
+		st['throws'](
+			getSymbolDescription,
+			SyntaxError,
+			'requires Symbol support'
+		);
+
+		st.end();
+	});
+
+	forEach(v.nonSymbolPrimitives.concat(v.objects), function (nonSymbol) {
+		t['throws'](
+			function () { getSymbolDescription(nonSymbol); },
+			TypeError,
+			debug(nonSymbol) + ' is not a Symbol'
+		);
+	});
+
+	t.test('with symbols', { skip: !v.hasSymbols }, function (st) {
+		forEach(
+			[
+				[Symbol(), undefined],
+				[Symbol(undefined), undefined],
+				[Symbol(null), 'null'],
+				[Symbol(''), ''],
+				[Symbol.iterator, 'Symbol.iterator'],
+				[Symbol('foo'), 'foo']
+			],
+			function (pair) {
+				var sym = pair[0];
+				var desc = pair[1];
+				st.equal(getSymbolDescription(sym), desc, debug(sym) + ' yields ' + debug(desc));
+			}
+		);
+
+		st.end();
+	});
+
+	t.end();
+});