Fix variable resolution in switch statements with let declarations

Fixed the regression introduced by 2ba6e57, which made `switch`
a proper `Scope`.

The issue was that `Scope.splitScope()` creates an outer block scope
and moves the symbol table from the switch to the block, but doesn't
update the switch's `parentScope` pointer. This breaks the scope chain
used for variable resolution, causing it to skip the block where
symbols are stored.

Fixed by manually fixing the scope chain, and follow the same pattern as
`transformForLoop()` for manually managing `currentScope` instead
of using `pushScope`/`popScope`, since the scope hierarchy is modified
after parsing.

Author: andreabergia

rhino/src/main/java/org/mozilla/javascript/IRFactory.java

@@ -1179,8 +1179,15 @@ private Node transformSwitch(SwitchStatement node) {
         Scope block = Scope.splitScope(node);
         block.setLineColumnNumber(node.getLineno(), node.getColumn());
         block.addChildToBack(node);
+        node.setParentScope(block);
 
-        parser.pushScope(node);
+        // Can't use pushScope/popScope here since splitScope moves the symbol table
+        // We set currentScope to 'node' (not 'block') so nested scopes can be pushed,
+        // since their parent pointers were set to 'node' during parsing. Variable resolution
+        // works correctly because it walks up the parentScope chain, where node.parentScope =
+        // block.
+        Scope savedScope = parser.currentScope;
+        parser.currentScope = node;
         try {
             Node switchExpr = transform(node.getExpression());
             node.addChildToBack(switchExpr);
@@ -1205,7 +1212,7 @@ private Node transformSwitch(SwitchStatement node) {
             closeSwitch(block);
             return block;
         } finally {
-            parser.popScope();
+            parser.currentScope = savedScope;
         }
     }
 

tests/src/test/java/org/mozilla/javascript/tests/es5/LetTest.java

@@ -94,4 +94,35 @@ void letInsideBodyOfSwitchES6Strict() {
                         + "})()\n";
         Utils.assertWithAllModes_ES6(1, script);
     }
+
+    @Test
+    void letInsideFunctionSwitchIf() {
+        String script =
+                "(function () {\n"
+                        + "    switch (0) {\n"
+                        + "        default:\n"
+                        + "            let a = 0;\n"
+                        + "            if (a == 0) {\n"
+                        + "                a++;\n"
+                        + "            }\n"
+                        + "            return a;\n"
+                        + "    }\n"
+                        + "})();\n";
+        Utils.assertWithAllModes_1_8(1, script);
+    }
+
+    @Test
+    void letInsideFunctionWhileIf() {
+        String script =
+                "(function () {\n"
+                        + "    while (true) {\n"
+                        + "            let a = 0;\n"
+                        + "            if (a == 0) {\n"
+                        + "                a++;\n"
+                        + "            }\n"
+                        + "            return a;\n"
+                        + "    }\n"
+                        + "})();\n";
+        Utils.assertWithAllModes_1_8(1, script);
+    }
 }