Log Java stack trace for uncaught JniExceptions

Summary: `JniException::what` is used as the abort message when a `JniException` is uncaught. It is currently missing the stack trace information you'd need to debug the underlying Java `Exception`.

Reviewed By: mhorowitz

Differential Revision: D55830419

fbshipit-source-id: 82992db5e60871cf78a779d56aa3528c2c8b8e68

cxx/fbjni/detail/Exceptions.cpp

@@ -427,7 +427,13 @@ local_ref<JThrowable> JniException::getThrowable() const noexcept {
 void JniException::populateWhat() const noexcept {
   try {
     ThreadScope ts;
-    what_ = throwable_->toString();
+    static auto exceptionHelperClass =
+        findClassStatic("com/facebook/jni/ExceptionHelper");
+    static auto getErrorDescriptionMethod =
+        exceptionHelperClass->getStaticMethod<std::string(jthrowable)>(
+            "getErrorDescription");
+    what_ = getErrorDescriptionMethod(exceptionHelperClass, throwable_.get())
+                ->toStdString();
     isMessageExtracted_ = true;
   } catch (...) {
     what_ = kExceptionMessageFailure;

java/com/facebook/jni/ExceptionHelper.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.facebook.jni;
+
+import com.facebook.jni.annotations.DoNotStrip;
+import java.io.PrintWriter;
+import java.io.StringWriter;
+
+@DoNotStrip
+class ExceptionHelper {
+  @DoNotStrip
+  private static String getErrorDescription(Throwable throwable) {
+    final StringWriter stringWriter = new StringWriter();
+    throwable.printStackTrace(new PrintWriter(stringWriter));
+    return stringWriter.toString();
+  }
+}

test/FBJniTests.java

@@ -639,23 +639,43 @@ public void testHandleNoRttiException() {
   @Test
   public void testCopyConstructor() {
     assertThat(nativeTestCopyConstructor())
-        .isEqualTo("com.facebook.jni.FBJniTests$CustomException: getMessages: 1");
+        .startsWith(
+            "com.facebook.jni.FBJniTests$CustomException: getMessages: 1\n"
+                + "\tat com.facebook.jni.FBJniTests.customExceptionThrower(FBJniTests.java:")
+        .contains(
+            ")\n"
+                + "\tat com.facebook.jni.FBJniTests.nativeTestCopyConstructor(Native Method)\n"
+                + "\tat com.facebook.jni.FBJniTests.testCopyConstructor(FBJniTests.java:");
   }
 
   private native String nativeTestCopyConstructor();
 
   @Test
   public void testMoveConstructorWithEmptyWhat() {
     assertThat(nativeTestMoveConstructorWithEmptyWhat())
-        .isEqualTo("com.facebook.jni.FBJniTests$CustomException: getMessages: 1");
+        .startsWith(
+            "com.facebook.jni.FBJniTests$CustomException: getMessages: 1\n"
+                + "\tat com.facebook.jni.FBJniTests.customExceptionThrower(FBJniTests.java:")
+        .contains(
+            ")\n"
+                + "\tat com.facebook.jni.FBJniTests.nativeTestMoveConstructorWithEmptyWhat(Native"
+                + " Method)\n"
+                + "\tat com.facebook.jni.FBJniTests.testMoveConstructorWithEmptyWhat(FBJniTests.java:");
   }
 
   private native String nativeTestMoveConstructorWithEmptyWhat();
 
   @Test
   public void testMoveConstructorWithPopulatedWhat() {
     assertThat(nativeTestMoveConstructorWithPopulatedWhat())
-        .isEqualTo("com.facebook.jni.FBJniTests$CustomException: getMessages: 1");
+        .startsWith(
+            "com.facebook.jni.FBJniTests$CustomException: getMessages: 1\n"
+                + "\tat com.facebook.jni.FBJniTests.customExceptionThrower(FBJniTests.java:")
+        .contains(
+            ")\n"
+                + "\tat com.facebook.jni.FBJniTests.nativeTestMoveConstructorWithPopulatedWhat(Native"
+                + " Method)\n"
+                + "\tat com.facebook.jni.FBJniTests.testMoveConstructorWithPopulatedWhat(FBJniTests.java:");
   }
 
   private native String nativeTestMoveConstructorWithPopulatedWhat();