Fix parsing error in exponent expressions with unary left-hand sides (#…

…201)

* Fix parsing error in exponent expressions with unary left-hand sides.

Esprima (correctly) rejects expressions like -1**2. - jquery/esprima#2070
However, expressions like (-1)**2 are valid but still rejected.
This commit fixes this issue by identifying when the left operand
is parenthesized.

Fixes jquery/esprima#1981

* add test for unary left side

src/Esprima/JavascriptParser.cs

@@ -1861,10 +1861,14 @@ private Expression ParseUnaryExpression()
 
  private Expression ParseExponentiationExpression()
  {
- var startToken = _lookahead;
-
- var expr = InheritCoverGrammar(parseUnaryExpression);
- if (expr.Type != Nodes.UnaryExpression && Match("**"))
+ var startToken = _lookahead;
+
+ var isLeftParenthesized = this.Match("(");
+ var expr = InheritCoverGrammar(parseUnaryExpression);
+
+ var exponentAllowed = expr.Type != Nodes.UnaryExpression || isLeftParenthesized;
+
+ if (exponentAllowed && Match("**"))
  {
  NextToken();
  _context.IsAssignmentTarget = false;

test/Esprima.Tests/Fixtures/invalid-syntax/unary_left_side.js

@@ -0,0 +1 @@
+(+2)**4;

test/Esprima.Tests/Fixtures/invalid-syntax/unary_left_side.tree.json

@@ -0,0 +1,112 @@
+{
+ "type": "Program",
+ "body": [
+ {
+ "type": "ExpressionStatement",
+ "expression": {
+ "type": "BinaryExpression",
+ "operator": "**",
+ "left": {
+ "type": "UnaryExpression",
+ "operator": "+",
+ "argument": {
+ "type": "Literal",
+ "value": 2,
+ "raw": "2",
+ "range": [
+ 2,
+ 3
+ ],
+ "loc": {
+ "start": {
+ "line": 1,
+ "column": 2
+ },
+ "end": {
+ "line": 1,
+ "column": 3
+ }
+ }
+ },
+ "prefix": true,
+ "range": [
+ 1,
+ 3
+ ],
+ "loc": {
+ "start": {
+ "line": 1,
+ "column": 1
+ },
+ "end": {
+ "line": 1,
+ "column": 3
+ }
+ }
+ },
+ "right": {
+ "type": "Literal",
+ "value": 4,
+ "raw": "4",
+ "range": [
+ 6,
+ 7
+ ],
+ "loc": {
+ "start": {
+ "line": 1,
+ "column": 6
+ },
+ "end": {
+ "line": 1,
+ "column": 7
+ }
+ }
+ },
+ "range": [
+ 0,
+ 7
+ ],
+ "loc": {
+ "start": {
+ "line": 1,
+ "column": 0
+ },
+ "end": {
+ "line": 1,
+ "column": 7
+ }
+ }
+ },
+ "range": [
+ 0,
+ 8
+ ],
+ "loc": {
+ "start": {
+ "line": 1,
+ "column": 0
+ },
+ "end": {
+ "line": 1,
+ "column": 8
+ }
+ }
+ }
+ ],
+ "sourceType": "script",
+ "range": [
+ 0,
+ 8
+ ],
+ "loc": {
+ "start": {
+ "line": 1,
+ "column": 0
+ },
+ "end": {
+ "line": 1,
+ "column": 8
+ }
+ }
+}