REPL mode must only re-write AST on successful parses

This CL fixes a parser crash in REPL mode. Some SyntaxErrors can cause
the AST to contain NULL nodes, resulting in a crash when we want to
rewrite the AST after parsing.

Instead of re-writing a broken AST we bail early.

R=leszeks@chromium.org

Bug: chromium:1040034, chromium:1045758
Change-Id: I9c559f6de5969c8db17833ccbdb1608627b46311
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2023547Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66008}

src/parsing/parser.cc

@@ -735,6 +735,8 @@ void Parser::ParseREPLProgram(ParseInfo* info, ScopedPtrList<Statement>* body,
     block = factory()->NewBlock(true, statements);
   }
 
+  if (has_error()) return;
+
   base::Optional<VariableProxy*> maybe_result =
       Rewriter::RewriteBody(info, scope, block->statements());
   Expression* result_value =

test/inspector/runtime/evaluate-repl-mode-expected.txt

 Tests that Runtime.evaluate works with REPL mode.
 Test 'let' re-declaration
+SyntaxError in REPL mode does not crash the parser
 {
     id : <messageId>
     result : {
@@ -36,3 +37,29 @@ Test 'let' re-declaration
         }
     }
 }
+{
+    id : <messageId>
+    result : {
+        exceptionDetails : {
+            columnNumber : 10
+            exception : {
+                className : SyntaxError
+                description : SyntaxError: Unexpected token 'const'
+                objectId : <objectId>
+                subtype : error
+                type : object
+            }
+            exceptionId : <exceptionId>
+            lineNumber : 0
+            scriptId : <scriptId>
+            text : Uncaught
+        }
+        result : {
+            className : SyntaxError
+            description : SyntaxError: Unexpected token 'const'
+            objectId : <objectId>
+            subtype : error
+            type : object
+        }
+    }
+}

test/inspector/runtime/evaluate-repl-mode.js

@@ -13,6 +13,10 @@ Protocol.Runtime.enable();
   evaluateRepl('let x = 42;');
   evaluateRepl('x;');
 
+  // Regression test for crbug.com/1040034.
+  InspectorTest.log("SyntaxError in REPL mode does not crash the parser");
+  evaluateRepl('if (true) const x');
+
   InspectorTest.completeTest();
 })();