[MSFT 13209141]: Defer default expressions in a formals list if the function containing them is going to be deferred. We know that the expressions can't be evaluated until the function has been fully compiled, so compiling the expressions up front is wasted work. And generating code for a function nested inside a deferred function creates inconsistencies.

pleath · pleath · commit 83090a9d6554 · 2017-08-29T14:54:12.000-07:00
diff --git a/lib/Parser/Parse.cpp b/lib/Parser/Parse.cpp
@@ -5195,7 +5195,7 @@ bool Parser::ParseFncDeclHelper(ParseNodePtr pnodeFnc, LPCOLESTR pNameHint, usho
                 saveDeferredStub = m_currDeferredStub;
                 m_currDeferredStub = nullptr;
             }
-            this->ParseFncFormals<buildAST>(pnodeFnc, pnodeFncParent, flags);
+            this->ParseFncFormals<buildAST>(pnodeFnc, pnodeFncParent, flags, isTopLevelDeferredFunc);
             if (buildAST)
             {
                 m_currDeferredStub = saveDeferredStub;
@@ -6227,7 +6227,7 @@ void Parser::UpdateOrCheckForDuplicateInFormals(IdentPtr pid, SList<IdentPtr> *f
 }
 
 template<bool buildAST>
-void Parser::ParseFncFormals(ParseNodePtr pnodeFnc, ParseNodePtr pnodeParentFnc, ushort flags)
+void Parser::ParseFncFormals(ParseNodePtr pnodeFnc, ParseNodePtr pnodeParentFnc, ushort flags, bool isTopLevelDeferredFunc)
 {
     bool fLambda = (flags & fFncLambda) != 0;
     bool fMethod = (flags & fFncMethod) != 0;
@@ -6439,9 +6439,21 @@ void Parser::ParseFncFormals(ParseNodePtr pnodeFnc, ParseNodePtr pnodeParentFnc,
                     }
 
                     m_pscan->Scan();
-                    ParseNodePtr pnodeInit = ParseExpr<buildAST>(koplCma, nullptr, TRUE, FALSE, pNameHint, &nameHintLength, &nameHintOffset);
 
-                    if (buildAST && pnodeInit->nop == knopFncDecl)
+                    ParseNodePtr pnodeInit;
+                    if (isTopLevelDeferredFunc)
+                    {
+                        // Defer default expressions if the function will be deferred, since we know they can't be evaluated
+                        // until the function is fully compiled, and generating code for a function nested inside a deferred function
+                        // creates inconsistencies.
+                        pnodeInit = ParseExpr<false>(koplCma, nullptr, TRUE, FALSE, pNameHint, &nameHintLength, &nameHintOffset);
+                    }
+                    else
+                    {
+                        pnodeInit = ParseExpr<buildAST>(koplCma, nullptr, TRUE, FALSE, pNameHint, &nameHintLength, &nameHintOffset);
+                    }
+
+                    if (buildAST && pnodeInit && pnodeInit->nop == knopFncDecl)
                     {
                         Assert(nameHintLength >= nameHintOffset);
                         pnodeInit->sxFnc.hint = pNameHint;
diff --git a/lib/Parser/Parse.h b/lib/Parser/Parse.h
@@ -773,7 +773,7 @@ class Parser
     template<bool buildAST> ParseNodePtr ParseMemberGetSet(OpCode nop, LPCOLESTR* ppNameHint);
     template<bool buildAST> ParseNodePtr ParseFncDecl(ushort flags, LPCOLESTR pNameHint = NULL, const bool needsPIDOnRCurlyScan = false, bool resetParsingSuperRestrictionState = true, bool fUnaryOrParen = false);
     template<bool buildAST> bool ParseFncNames(ParseNodePtr pnodeFnc, ParseNodePtr pnodeFncParent, ushort flags, ParseNodePtr **pLastNodeRef);
-    template<bool buildAST> void ParseFncFormals(ParseNodePtr pnodeFnc, ParseNodePtr pnodeParentFnc, ushort flags);
+    template<bool buildAST> void ParseFncFormals(ParseNodePtr pnodeFnc, ParseNodePtr pnodeParentFnc, ushort flags, bool isTopLevelDeferredFunc = false);
     template<bool buildAST> bool ParseFncDeclHelper(ParseNodePtr pnodeFnc, LPCOLESTR pNameHint, ushort flags, bool *pHasName, bool fUnaryOrParen, bool noStmtContext, bool *pNeedScanRCurly, bool skipFormals = false);
     template<bool buildAST> void ParseExpressionLambdaBody(ParseNodePtr pnodeFnc);
     template<bool buildAST> void UpdateCurrentNodeFunc(ParseNodePtr pnodeFnc, bool fLambda);
diff --git a/test/es6/classes_bugfixes.js b/test/es6/classes_bugfixes.js
@@ -464,6 +464,16 @@ var tests = [
         assert.areEqual('Bsetter;Bgetter;', result);
     }
   },
+  {
+    name: "MSFT:13209141: Confusion on deferred function containing non-deferred extends cause calling eval",
+    body: function () {
+      function foo(a = class c extends eval("") {}) {}
+      try {
+        foo();
+      }
+      catch(e) {}
+    }
+  },
 ];
 
 testRunner.runTests(tests, { verbose: WScript.Arguments[0] != "summary" });
