fix(#74): correct exponentiation precedence

Closes #74.

Author: davidbonnet

docs/demo/astring.min.js

@@ -113,7 +113,13 @@ function expressionNeedsParenthesis(node, parentNode, isRightHand) {
   const parentNodePrecedence = EXPRESSIONS_PRECEDENCE[parentNode.type]
   if (nodePrecedence !== parentNodePrecedence) {
     // Different node types
-    return nodePrecedence < parentNodePrecedence
+    return (
+      (!isRightHand &&
+        nodePrecedence === 15 &&
+        parentNodePrecedence === 14 &&
+        parentNode.operator === '**') ||
+      nodePrecedence < parentNodePrecedence
+    )
   }
   if (nodePrecedence !== 13 && nodePrecedence !== 14) {
     // Not a `LogicalExpression` or `BinaryExpression`
@@ -843,17 +849,16 @@ export const baseGenerator = {
     this[node.right.type](node.right, state)
   },
   BinaryExpression: (BinaryExpression = function(node, state) {
-    if (node.operator === 'in') {
+    const isIn = node.operator === 'in'
+    if (isIn) {
       // Avoids confusion in `for` loops initializers
       state.write('(')
-      formatBinaryExpressionPart(state, node.left, node, false)
-      state.write(' ' + node.operator + ' ')
-      formatBinaryExpressionPart(state, node.right, node, true)
+    }
+    formatBinaryExpressionPart(state, node.left, node, false)
+    state.write(' ' + node.operator + ' ')
+    formatBinaryExpressionPart(state, node.right, node, true)
+    if (isIn) {
       state.write(')')
-    } else {
-      formatBinaryExpressionPart(state, node.left, node, false)
-      state.write(' ' + node.operator + ' ')
-      formatBinaryExpressionPart(state, node.right, node, true)
     }
   }),
   LogicalExpression: BinaryExpression,

docs/demo/astring.min.js.map

@@ -24,6 +24,8 @@ var r = (/ab+c/i).exec('abc');
 a = b ** 2 * 3;
 c = (d ** 2) ** 3;
 e = f ** 2 ** 3;
+e = (+2) ** 3;
+e = 2 ** +3;
 f = a + (b = 3);
 g = 1 && (() => {});
 g = (() => {}) && 1;

src/astring.js

@@ -39,7 +39,12 @@ test('Syntax check', assert => {
   files.forEach(filename => {
     const code = readFile(path.join(dirname, filename))
     const ast = parse(code, options)
-    assert.is(generate(ast), code, filename.substring(0, filename.length - 3))
+    assert.is(
+      generate(ast),
+      code,
+      filename.substring(0, filename.length - 3),
+      'Generates code with the expected format',
+    )
   })
 })
 
@@ -60,6 +65,7 @@ test('Tree comparison', assert => {
       formattedAst,
       ast,
       filename.substring(0, filename.length - 3),
+      'Generates code with the same meaning',
     )
   })
 })