Add a scope in while loops

Summary:
Emit a scope in while loops, so that lexically scoped declarations in
the loop will have a different instance on each iteration.

Reviewed By: avp

Differential Revision: D56026167

fbshipit-source-id: 77cadc4e4d72b86f820bb183a5bd4ccbde498029

lib/IRGen/ESTreeIRGen-stmt.cpp

@@ -294,7 +294,25 @@ void ESTreeIRGen::genWhileLoop(ESTree::WhileStatementNode *loop) {
   genExpressionBranch(loop->_test, bodyBlock, exitBlock, nullptr);
   // Generate the body.
   Builder.setInsertionBlock(bodyBlock);
+
+  // Save the outer scope in case we create an inner scope.
+  auto *outerScope = curFunction()->curScope;
+
+  // If the body captures, create an inner scope for it. Note that unlike for
+  // loops, we don't care whether the test expression captures, since the loop
+  // does not create variables visible in the test expression.
+  if (Mod->getContext().getEnableES6BlockScoping() &&
+      !treeDoesNotCapture(loop->_body)) {
+    auto *bodyVarScope = curFunction()->getOrCreateInnerVariableScope(loop);
+    auto *bodyScope = Builder.createCreateScopeInst(bodyVarScope, outerScope);
+    curFunction()->curScope = bodyScope;
+  }
+
   genStatement(loop->_body);
+
+  // Restore the outer scope.
+  curFunction()->curScope = outerScope;
+
   // After executing the content of the body, jump to the post test block.
   Builder.createBranchInst(postTestBlock);
   Builder.setInsertionBlock(postTestBlock);

test/hermes/while-finally-nested.js

@@ -0,0 +1,44 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// RUN: %hermes %s -Xes6-block-scoping | %FileCheck --match-full-lines %s
+// RUN: %hermes -Xes6-block-scoping -lazy %s | %FileCheck --match-full-lines %s
+// RUN: %shermes -Xes6-block-scoping -exec %s | %FileCheck --match-full-lines %s
+
+let arr = (function (){
+  let arr = [];
+  try {
+    while (true) {
+      let x = 42;
+      // Make sure there is a capture to force a scope.
+      arr.push(()=>x);
+      return arr;
+    }
+  } finally {
+    // Test that emitting this finally block at the location of the return above
+    // (which is a different scope in the IR) works correctly.
+    while (arr.length < 10) {
+      let x = arr.length;
+      arr.push(()=>x);
+    }
+  }
+})();
+
+for (v of arr){
+  print(v());
+}
+
+// CHECK: 42
+// CHECK-NEXT: 1
+// CHECK-NEXT: 2
+// CHECK-NEXT: 3
+// CHECK-NEXT: 4
+// CHECK-NEXT: 5
+// CHECK-NEXT: 6
+// CHECK-NEXT: 7
+// CHECK-NEXT: 8
+// CHECK-NEXT: 9

test/hermes/while-let-capture.js

@@ -0,0 +1,34 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// RUN: %hermes -Xes6-block-scoping %s | %FileCheck --match-full-lines %s
+// RUN: %shermes -Xes6-block-scoping -exec %s | %FileCheck --match-full-lines %s
+
+(function (){
+  let arr = [];
+  let i = 0;
+  while (i < 10) {
+    let j = i;
+    arr.push(()=>j);
+    i++;
+  }
+
+  for(f of arr) {
+    print(f());
+  }
+})();
+
+// CHECK: 0
+// CHECK-NEXT: 1
+// CHECK-NEXT: 2
+// CHECK-NEXT: 3
+// CHECK-NEXT: 4
+// CHECK-NEXT: 5
+// CHECK-NEXT: 6
+// CHECK-NEXT: 7
+// CHECK-NEXT: 8
+// CHECK-NEXT: 9