fix($parse): validate assignment lval in parser phase

The parser always threw an error in the case of an invalid left-value
assignment but it was an unhelpful:

```
Cannot set property 'undefined' of undefined
```

This commit provides a more meaningful error message, so it is not a
breaking change.

Closes angular#15234

Author: jbedard

src/ng/parse.js

@@ -436,6 +436,10 @@ AST.prototype = {
   assignment: function() {
     var result = this.ternary();
     if (this.expect('=')) {
+      if (!isAssignable(result)) {
+        throw $parseMinErr('lval', 'Trying to assign a value to a non l-value');
+      }
+
       result = { type: AST.AssignmentExpression, left: result, right: this.assignment(), operator: '='};
     }
     return result;
@@ -1148,9 +1152,6 @@ ASTCompiler.prototype = {
     case AST.AssignmentExpression:
       right = this.nextId();
       left = {};
-      if (!isAssignable(ast.left)) {
-        throw $parseMinErr('lval', 'Trying to assign a value to a non l-value');
-      }
       this.recurse(ast.left, undefined, left, function() {
         self.if_(self.notNull(left.context), function() {
           self.recurse(ast.right, right);

test/ng/parseSpec.js

@@ -2128,6 +2128,20 @@ describe('parser', function() {
         expect(scope.b).toEqual(234);
       });
 
+      it('should throw with invalid left-val in assignments', function() {
+        expect(function() { scope.$eval('1 = 1'); }).toThrowMinErr('$parse', 'lval');
+        expect(function() { scope.$eval('{} = 1'); }).toThrowMinErr('$parse', 'lval');
+        expect(function() { scope.$eval('[] = 1'); }).toThrowMinErr('$parse', 'lval');
+        expect(function() { scope.$eval('true = 1'); }).toThrowMinErr('$parse', 'lval');
+        expect(function() { scope.$eval('(a=b) = 1'); }).toThrowMinErr('$parse', 'lval');
+        expect(function() { scope.$eval('(1<2) = 1'); }).toThrowMinErr('$parse', 'lval');
+        expect(function() { scope.$eval('(1+2) = 1'); }).toThrowMinErr('$parse', 'lval');
+        expect(function() { scope.$eval('!v = 1'); }).toThrowMinErr('$parse', 'lval');
+        expect(function() { scope.$eval('this = 1'); }).toThrowMinErr('$parse', 'lval');
+        expect(function() { scope.$eval('+v = 1'); }).toThrowMinErr('$parse', 'lval');
+        expect(function() { scope.$eval('(1?v1:v2) = 1'); }).toThrowMinErr('$parse', 'lval');
+      });
+
       it('should evaluate assignments in ternary operator', function() {
         scope.$eval('a = 1 ? 2 : 3');
         expect(scope.a).toBe(2);