throw error on illegal context (#934)

src/parse/state/mustache.ts

@@ -1,6 +1,7 @@
 import readExpression from '../read/expression';
 import { whitespace } from '../../utils/patterns';
 import { trimStart, trimEnd } from '../../utils/trim';
+import reservedNames from '../../utils/reservedNames';
 import { Parser } from '../index';
 import { Node } from '../../interfaces';
 
@@ -168,8 +169,15 @@ export default function mustache(parser: Parser) {
 
 				do {
 					parser.allowWhitespace();
+
+					const start = parser.index;
 					const destructuredContext = parser.read(validIdentifier);
+
 					if (!destructuredContext) parser.error(`Expected name`);
+					if (reservedNames.has(destructuredContext)) {
+						parser.error(`'${destructuredContext}' is a reserved word in JavaScript and cannot be used here`, start);
+					}
+
 					block.destructuredContexts.push(destructuredContext);
 					parser.allowWhitespace();
 				} while (parser.eat(','));
@@ -180,7 +188,11 @@ export default function mustache(parser: Parser) {
 				parser.allowWhitespace();
 				parser.eat(']', true);
 			} else {
-				block.context = parser.read(validIdentifier); // TODO check it's not a keyword
+				const start = parser.index;
+				block.context = parser.read(validIdentifier);
+				if (reservedNames.has(block.context)) {
+					parser.error(`'${block.context}' is a reserved word in JavaScript and cannot be used here`, start);
+				}
 
 				if (!block.context) parser.error(`Expected name`);
 			}

src/utils/reservedNames.ts

@@ -49,7 +49,4 @@ const reservedNames = new Set([
 	'yield',
 ]);
 
-// prevent e.g. `{{#each states as state}}` breaking
-reservedNames.add('state');
-
 export default reservedNames;

test/validator/samples/each-block-invalid-context-destructured/errors.json

@@ -0,0 +1,8 @@
+[{
+	"message": "'case' is a reserved word in JavaScript and cannot be used here",
+	"loc": {
+		"line": 1,
+		"column": 18
+	},
+	"pos": 18
+}]

test/validator/samples/each-block-invalid-context-destructured/input.html

@@ -0,0 +1,3 @@
+{{#each cases as [case]}}
+	{{case.title}}
+{{/each}}

test/validator/samples/each-block-invalid-context/errors.json

@@ -0,0 +1,8 @@
+[{
+	"message": "'case' is a reserved word in JavaScript and cannot be used here",
+	"loc": {
+		"line": 1,
+		"column": 17
+	},
+	"pos": 17
+}]

test/validator/samples/each-block-invalid-context/input.html

@@ -0,0 +1,3 @@
+{{#each cases as case}}
+	{{case.title}}
+{{/each}}