Handle REPL 'let' declared variables properly for 'delete'

REPL 'let' declared variables use VariableLocation::REPL_GLOBAL which
was not handled by a switch in the bytecode generator. The default
case ran into an UNREACHABLE.

This CL fixes this by properly handling VariableLocation::REPL_GLOBAL
for delete.

Drive-by: Replaced the default case with an explicit case for
VariableLocation::MODULE.

Bug: chromium:1052721
Change-Id: I1330ff2f2c6f042a596a8298599a5d58769894f3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2060488
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66301}

src/interpreter/bytecode-generator.cc

@@ -5124,7 +5124,8 @@ void BytecodeGenerator::VisitDelete(UnaryOperation* unary) {
     switch (variable->location()) {
       case VariableLocation::PARAMETER:
       case VariableLocation::LOCAL:
-      case VariableLocation::CONTEXT: {
+      case VariableLocation::CONTEXT:
+      case VariableLocation::REPL_GLOBAL: {
         // Deleting local var/let/const, context variables, and arguments
         // does not have any effect.
         builder()->LoadFalse();
@@ -5145,7 +5146,9 @@ void BytecodeGenerator::VisitDelete(UnaryOperation* unary) {
             .CallRuntime(Runtime::kDeleteLookupSlot, name_reg);
         break;
       }
-      default:
+      case VariableLocation::MODULE:
+        // Modules are always in strict mode and unqualified identifers are not
+        // allowed in strict mode.
         UNREACHABLE();
     }
   } else {

test/inspector/runtime/regression-1052721-expected.txt

+Deleting REPL let does not crash V8 crbug.com/105271
+
+Running test: deleteReplLetDeclaration
+{
+    id : <messageId>
+    result : {
+        result : {
+            type : boolean
+            value : false
+        }
+    }
+}

test/inspector/runtime/regression-1052721.js

+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+let {session, contextGroup, Protocol} = InspectorTest.start('Deleting REPL let does not crash V8 crbug.com/105271');
+
+InspectorTest.runAsyncTestSuite([
+  async function deleteReplLetDeclaration() {
+    await Protocol.Runtime.enable();
+    const response = await Protocol.Runtime.evaluate({
+      expression: 'let x = 1; delete x;',
+      replMode: true,
+    });
+    InspectorTest.logMessage(response);
+    await Protocol.Runtime.disable();
+  }
+]);