wasm gc: improve exception stack trace when exception is thrown from wasm and rethrown between Java and JS

classlib/src/main/java/org/teavm/classlib/java/lang/TThrowable.java

@@ -111,10 +111,14 @@ public class TThrowable extends RuntimeException {
             stackTrace = (TStackTraceElement[]) (Object) ExceptionHandling.fillStackTrace();
         } else if (PlatformDetector.isWebAssemblyGC()) {
             lazyStackTrace = takeWasmGCStack();
+            decorateException(this);
         }
         return this;
     }
 
+    @Import(name = "decorateException")
+    private static native void decorateException(Object obj);
+
     private void ensureStackTrace() {
         if (PlatformDetector.isWebAssemblyGC()) {
             if (lazyStackTrace != null) {

core/src/main/java/org/teavm/backend/wasm/WasmGCTarget.java

@@ -46,8 +46,13 @@ import org.teavm.backend.wasm.intrinsics.gc.WasmGCIntrinsicFactory;
 import org.teavm.backend.wasm.intrinsics.gc.WasmGCIntrinsics;
 import org.teavm.backend.wasm.model.WasmCustomSection;
 import org.teavm.backend.wasm.model.WasmFunction;
+import org.teavm.backend.wasm.model.WasmLocal;
 import org.teavm.backend.wasm.model.WasmModule;
 import org.teavm.backend.wasm.model.WasmTag;
+import org.teavm.backend.wasm.model.WasmType;
+import org.teavm.backend.wasm.model.expression.WasmGetLocal;
+import org.teavm.backend.wasm.model.expression.WasmStructGet;
+import org.teavm.backend.wasm.model.expression.WasmStructSet;
 import org.teavm.backend.wasm.optimization.WasmUsageCounter;
 import org.teavm.backend.wasm.render.WasmBinaryRenderer;
 import org.teavm.backend.wasm.render.WasmBinaryStatsCollector;
@@ -279,11 +284,46 @@ public class WasmGCTarget implements TeaVMTarget, TeaVMWasmGCHost {
 
         moduleGenerator.generate();
         customGenerators.contributeToModule(module);
+        generateExceptionExports(declarationsGenerator);
         adjustModuleMemory(module);
 
         emitWasmFile(module, buildTarget, outputName, debugInfoBuilder);
     }
 
+    private void generateExceptionExports(WasmGCDeclarationsGenerator declarationsGenerator) {
+        var nativeExceptionField = declarationsGenerator.classInfoProvider().getThrowableNativeOffset();
+        if (nativeExceptionField < 0) {
+            return;
+        }
+
+        var throwableType = declarationsGenerator.classInfoProvider().getClassInfo("java.lang.Throwable")
+                .getStructure();
+
+        var getFunction = new WasmFunction(declarationsGenerator.functionTypes.of(
+                WasmType.Reference.EXTERN, throwableType.getReference()
+        ));
+        getFunction.setName("teavm.getJsException");
+        getFunction.setExportName("teavm.getJsException");
+        var getParam = new WasmLocal(throwableType.getReference(), "javaException");
+        getFunction.add(getParam);
+        var getField = new WasmStructGet(throwableType, new WasmGetLocal(getParam), nativeExceptionField);
+        getFunction.getBody().add(getField);
+        declarationsGenerator.module.functions.add(getFunction);
+
+        var setFunction = new WasmFunction(declarationsGenerator.functionTypes.of(null, throwableType.getReference(),
+                WasmType.Reference.EXTERN));
+        setFunction.setName("teavm.setJsException");
+        setFunction.setExportName("teavm.setJsException");
+        var setParam = new WasmLocal(throwableType.getReference(), "javaException");
+        var setValue = new WasmLocal(WasmType.Reference.EXTERN, "jsException");
+        setFunction.add(setParam);
+        setFunction.add(setValue);
+        var setField = new WasmStructSet(throwableType, new WasmGetLocal(setParam),
+                nativeExceptionField, new WasmGetLocal(setValue));
+        setFunction.getBody().add(setField);
+        declarationsGenerator.module.functions.add(setFunction);
+    }
+
     private WasmGCClassConsumerContext createClassConsumerContext(
             ClassReaderSource classes,
             WasmGCDeclarationsGenerator generator

core/src/main/java/org/teavm/backend/wasm/generate/gc/classes/WasmGCClassGenerator.java

@@ -147,6 +147,7 @@ public class WasmGCClassGenerator implements WasmGCClassInfoProvider, WasmGCInit
     private int arrayCopyOffset = -1;
     private int cloneOffset = -1;
     private int servicesOffset = -1;
+    private int throwableNativeOffset = -1;
     private WasmStructure arrayVirtualTableStruct;
     private WasmFunction arrayGetObjectFunction;
     private WasmFunction arrayLengthObjectFunction;
@@ -482,6 +483,11 @@ public class WasmGCClassGenerator implements WasmGCClassInfoProvider, WasmGCInit
         return servicesOffset;
     }
 
+    @Override
+    public int getThrowableNativeOffset() {
+        return throwableNativeOffset;
+    }
+
     private void initPrimitiveClass(WasmGCClassInfo classInfo, ValueType.Primitive type) {
         classInfo.initializer = target -> {
             int kind;
@@ -1221,6 +1227,11 @@ public class WasmGCClassGenerator implements WasmGCClassInfoProvider, WasmGCInit
             var field = new WasmField(WasmType.Reference.EXTERN.asStorage(), "nativeRef");
             fields.add(field);
         }
+        if (className.equals("java.lang.Throwable")) {
+            throwableNativeOffset = fields.size();
+            var field = new WasmField(WasmType.Reference.EXTERN.asStorage(), "nativeRef");
+            fields.add(field);
+        }
         if (className.equals("java.lang.Class")) {
             var cls = classSource.get("java.lang.Class");
             classFlagsOffset = fields.size();

core/src/main/java/org/teavm/backend/wasm/generate/gc/classes/WasmGCClassInfoProvider.java

@@ -73,6 +73,8 @@ public interface WasmGCClassInfoProvider {
 
     int getServicesOffset();
 
+    int getThrowableNativeOffset();
+
     default WasmGCClassInfo getClassInfo(String name) {
         return getClassInfo(ValueType.object(name));
     }

core/src/main/js/wasm-gc-runtime/runtime.js

@@ -58,6 +58,7 @@ class JavaError extends Error {
         super();
         this.#context = context;
         this[javaExceptionSymbol] = javaException;
+        context.exports["teavm.setJsException"](javaException, this);
     }
     get message() {
         let exceptionMessage = this.#context.exports["teavm.exceptionMessage"];
@@ -180,6 +181,9 @@ function coreImports(imports, context) {
                     return result;
                 }
             };
+        },
+        decorateException(javaException) {
+            new JavaError(context, javaException);
         }
     };
 }
@@ -195,7 +199,6 @@ function jsoImports(imports, context) {
     let primitiveWrappers = new Map();
     let primitiveFinalization = new FinalizationRegistry(token => primitiveWrappers.delete(token));
     let hashCodes = new WeakMap();
-    let javaExceptionWrappers = new WeakMap();
     let lastHashCode = 2463534242;
     let nextHashCode = () => {
         let x = lastHashCode;
@@ -235,21 +238,17 @@ function jsoImports(imports, context) {
     function javaExceptionToJs(e) {
         if (e instanceof WebAssembly.Exception) {
             let tag = context.exports["teavm.javaException"];
+            let getJsException = context.exports["teavm.getJsException"];
             if (e.is(tag)) {
                 let javaException = e.getArg(tag, 0);
                 let extracted = extractException(javaException);
                 if (extracted !== null) {
                     return extracted;
                 }
-                let wrapperRef = javaExceptionWrappers.get(javaException);
+                let wrapper = getJsException(javaException);
-                if (typeof wrapperRef != "undefined") {
+                if (typeof wrapper === "undefined") {
-                    let wrapper = wrapperRef.deref();
+                    wrapper = new JavaError(context, javaException);
-                    if (typeof wrapper !== "undefined") {
-                        return wrapper;
-                    }
                 }
-                let wrapper = new JavaError(context, javaException);
-                javaExceptionWrappers.set(javaException, new WeakRef(wrapper));
                 return wrapper;
             }
         }