don't throw wasm compile exception after finishing bytecode gen

lib/WasmReader/WasmByteCodeGenerator.cpp

@@ -483,10 +483,6 @@ void WasmBytecodeGenerator::GenerateFunctionBytecode(Js::ScriptContext* scriptCo
 {
     WasmBytecodeGenerator generator(scriptContext, readerinfo, validateOnly);
     generator.GenerateFunction();
-    if (!generator.GetReader()->IsCurrentFunctionCompleted())
-    {
-        throw WasmCompilationException(_u("Invalid function format"));
-    }
 }
 
 void WasmBytecodeGenerator::ValidateFunction(Js::ScriptContext* scriptContext, WasmReaderInfo* readerinfo)
@@ -548,7 +544,12 @@ void WasmBytecodeGenerator::GenerateFunction()
                 gen->m_originalWriter->Reset();
             }
         }
-        void Complete() { gen = nullptr; }
+        void Complete()
+        {
+            gen->m_writer->End();
+            gen->GetReader()->FunctionEnd();
+            gen = nullptr;
+        }
     };
     AutoCleanupGeneratorState autoCleanupGeneratorState(this);
     Js::ByteCodeLabel exitLabel = m_writer->DefineLabel();
@@ -574,8 +575,12 @@ void WasmBytecodeGenerator::GenerateFunction()
     m_writer->MarkAsmJsLabel(exitLabel);
     m_writer->EmptyAsm(Js::OpCodeAsmJs::Ret);
     m_writer->SetCallSiteCount(this->currentProfileId);
-    m_writer->End();
-    GetReader()->FunctionEnd();
+
+    if (!GetReader()->IsCurrentFunctionCompleted())
+    {
+        throw WasmCompilationException(_u("Invalid function format"));
+    }
+
     autoCleanupGeneratorState.Complete();
     // Make sure we don't have any unforeseen exceptions as we finalize the body
     AutoDisableInterrupt autoDisableInterrupt(m_scriptContext->GetThreadContext(), true);

test/wasm/badfuncformat.js

@@ -0,0 +1,18 @@
+//-------------------------------------------------------------------------------------------------------
+// Copyright (C) Microsoft Corporation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE.txt file in the project root for full license information.
+//-------------------------------------------------------------------------------------------------------
+
+var wasmCode = new Uint8Array([0,97,115,109,1,0,0,0,1,5,1,96,0,1,127,3,2,1,0,5,4,1,1,0,0,7,5,1,1,102,0,0,10,6,1,4,0,0,11,11,0,11,4,110,97,109,101,1,4,1,0,1,102]);
+var wasmModule = new WebAssembly.Module(wasmCode);
+var wasmInstance = new WebAssembly.Instance(wasmModule, {});
+let threw = false;
+try
+{
+    wasmInstance.exports.f();
+}
+catch(e)
+{
+    threw = true;
+}
+print(threw ? "Pass" : "Fail");

test/wasm/rlexe.xml

@@ -164,6 +164,11 @@
     <compile-flags>-wasm</compile-flags>
   </default>
 </test>
+<test>
+  <default>
+    <files>badfuncformat.js</files>
+  </default>
+</test>
 <test>
   <default>
     <files>table_imports.js</files>