Log a backtrace on panic

RELEASE_NOTES.md

@@ -6,3 +6,5 @@ v0.91.0
 - Add `UserBasedAuthorization.UnrestrictedUnauthenticatedAccess` / `unrestrictedUnauthenticatedAccess` / `'unrestricted'` for `UnauthKeysService.getPreKeys` (and for 1:1 sealed sender messages in the future).
 
 - Log more details on gRPC failure
+
+- Log backtraces on panic

java/android/src/androidTest/java/org/signal/libsignal/util/AndroidJUnitRunner.java

@@ -17,7 +17,8 @@ public class AndroidJUnitRunner extends androidx.test.runner.AndroidJUnitRunner
     super.onCreate(bundle);
 
     // Make sure libsignal logs get caught correctly.
-    SignalProtocolLoggerProvider.setProvider(new AndroidSignalProtocolLogger());
+    SignalProtocolLoggerProvider.setProvider(
+        new TestLoggerDecorator(new AndroidSignalProtocolLogger()));
     SignalProtocolLoggerProvider.initializeLogging(SignalProtocolLogger.VERBOSE);
 
     // Propagate any "environment variables" the test might need into System properties.

java/server/build.gradle

@@ -42,12 +42,13 @@ sourceSets {
 
 dependencies {
     testImplementation 'junit:junit:4.13'
+    testImplementation 'org.jetbrains.kotlin:kotlin-test:2.1.0'
 }
 
 test {
     jvmArgs '-Xcheck:jni'
     testLogging {
-        events 'passed','skipped','failed'
+        events 'passed', 'skipped', 'failed'
         showStandardStreams = true
         showExceptions = true
         exceptionFormat = 'full'

java/shared/test/java/org/signal/libsignal/PanicLogTest.kt

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2026 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.signal.libsignal
+
+import org.junit.Assert
+import org.junit.ClassRule
+import org.junit.Test
+import org.junit.function.ThrowingRunnable
+import org.signal.libsignal.internal.NativeTesting
+import org.signal.libsignal.util.TestLogger
+import org.signal.libsignal.util.TestLoggerDecorator
+import kotlin.test.assertContains
+import kotlin.test.assertEquals
+
+class PanicLogTest {
+  companion object {
+    @ClassRule
+    @JvmField
+    val logger = TestLogger()
+  }
+
+  @Test
+  public fun testPanicsLog() {
+    TestLoggerDecorator.logs.set(mutableListOf())
+    try {
+      Assert.assertThrows(
+        AssertionError::class.java,
+        ThrowingRunnable {
+          @Suppress("PLATFORM_CLASS_MAPPED_TO_KOTLIN")
+          NativeTesting.TESTING_PanicOnBorrowSync("123" as Object)
+        },
+      )
+      val logs = TestLoggerDecorator.logs.get()!!
+      assertEquals(1, logs.size)
+      assertContains(logs[0].message, "panicked at")
+    } finally {
+      TestLoggerDecorator.logs.set(null)
+    }
+  }
+}

java/shared/test/java/org/signal/libsignal/util/TestLogger.java

@@ -27,7 +27,7 @@ public class TestLogger extends ExternalResource {
     }
 
     SignalProtocolLoggerProvider.initializeLogging(SignalProtocolLogger.VERBOSE);
-    SignalProtocolLoggerProvider.setProvider(new StderrLogger());
+    SignalProtocolLoggerProvider.setProvider(new TestLoggerDecorator(new StderrLogger()));
   }
 
   @Override

java/shared/test/java/org/signal/libsignal/util/TestLoggerDecorator.kt

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2026 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.signal.libsignal.util
+
+import org.signal.libsignal.protocol.logging.SignalProtocolLogger
+
+public class TestLoggerDecorator(
+  private val inner: SignalProtocolLogger,
+) : SignalProtocolLogger {
+  public data class LogRecord(
+    val priority: Int,
+    val tag: String,
+    val message: String,
+  )
+
+  companion object {
+    public val logs = ThreadLocal<MutableList<LogRecord>>()
+  }
+
+  override fun log(
+    priority: Int,
+    tag: String?,
+    message: String?,
+  ) {
+    logs.get()?.add(LogRecord(priority, tag!!, message!!))
+    inner.log(priority, tag, message)
+  }
+}

rust/bridge/shared/src/logging.rs

@@ -30,7 +30,9 @@ pub fn log_enabled_in_apps(metadata: &log::Metadata) -> bool {
         // Other libsignal crates:
         b'a' => check("attest"),
         b'd' => check("device_transfer"),
-        b'p' => check("poksho"),
+        // target == "panic" isn't a libsignal crate, it's the log_panics crate
+        // In log_panics, they manually override the log target to be "panic" rather than log_panics
+        b'p' => check("poksho") || target == "panic",
         b'u' => check("usernames"),
         b'z' => check("zkgroup") || check("zkcredential"),
 
@@ -49,6 +51,16 @@ mod tests {
 
     use super::*;
 
+    #[test]
+    fn test_panic() {
+        assert!(log_enabled_in_apps(
+            &log::Metadata::builder()
+                .target("panic")
+                .level(log::Level::Error)
+                .build()
+        ));
+    }
+
     #[test_matrix([
         "libsignal_foo",
         "signal_foo",