Merge pull request #31480 from andrewbranch/bug/25487

Fix invalid JSXExpressions having identifier-ish things in their trivia, improve error messages for comma expressions in JSX

src/compiler/checker.ts

@@ -20033,6 +20033,7 @@ namespace ts {
         }
 
         function checkJsxExpression(node: JsxExpression, checkMode?: CheckMode) {
+            checkGrammarJsxExpression(node);
             if (node.expression) {
                 const type = checkExpression(node.expression, checkMode);
                 if (node.dotDotDotToken && type !== anyType && !isArrayType(type)) {
@@ -31912,6 +31913,12 @@ namespace ts {
             }
         }
 
+        function checkGrammarJsxExpression(node: JsxExpression) {
+            if (node.expression && isCommaSequence(node.expression)) {
+                return grammarErrorOnNode(node.expression, Diagnostics.JSX_expressions_may_not_use_the_comma_operator_Did_you_mean_to_write_an_array);
+            }
+        }
+
         function checkGrammarForInOrForOfStatement(forInOrOfStatement: ForInOrOfStatement): boolean {
             if (checkGrammarStatementInAmbientContext(forInOrOfStatement)) {
                 return true;

src/compiler/diagnosticMessages.json

@@ -5009,5 +5009,9 @@
     "Classes may not have a field named 'constructor'.": {
         "category": "Error",
         "code": 18006
+    },
+    "JSX expressions may not use the comma operator. Did you mean to write an array?": {
+        "category": "Error",
+        "code": 18007
     }
 }

src/compiler/parser.ts

@@ -4430,14 +4430,18 @@ namespace ts {
 
             if (token() !== SyntaxKind.CloseBraceToken) {
                 node.dotDotDotToken = parseOptionalToken(SyntaxKind.DotDotDotToken);
-                node.expression = parseAssignmentExpressionOrHigher();
+                // Only an AssignmentExpression is valid here per the JSX spec,
+                // but we can unambiguously parse a comma sequence and provide
+                // a better error message in grammar checking.
+                node.expression = parseExpression();
             }
             if (inExpressionContext) {
                 parseExpected(SyntaxKind.CloseBraceToken);
             }
             else {
-                parseExpected(SyntaxKind.CloseBraceToken, /*message*/ undefined, /*shouldAdvance*/ false);
-                scanJsxText();
+                if (parseExpected(SyntaxKind.CloseBraceToken, /*message*/ undefined, /*shouldAdvance*/ false)) {
+                    scanJsxText();
+                }
             }
 
             return finishNode(node);