kotlin: use Throwable.stackTraceToString to show more info

Author: flisky

fixtures/callbacks/tests/bindings/test_callbacks.kts

@@ -102,7 +102,7 @@ try {
     throw RuntimeException("Expected ComplexException.UnexpectedErrorWithReason")
 } catch (e: ComplexException.UnexpectedErrorWithReason) {
     // Expected error
-    assert(e.reason == RuntimeException("something failed").toString())
+    assert(e.reason.startsWith(RuntimeException("something failed").toString()))
 }
 
 

uniffi_bindgen/src/bindings/kotlin/templates/Helpers.kt

@@ -102,8 +102,9 @@ internal inline fun<T> uniffiTraitInterfaceCall(
     try {
         writeReturn(makeCall())
     } catch(e: kotlin.Exception) {
+        val err = try { e.stackTraceToString() } catch(_: Throwable) { "" }
         callStatus.code = UNIFFI_CALL_UNEXPECTED_ERROR
-        callStatus.error_buf = {{ Type::String.borrow()|lower_fn }}(e.toString())
+        callStatus.error_buf = {{ Type::String.borrow()|lower_fn }}(err)
     }
 }
 
@@ -120,8 +121,9 @@ internal inline fun<T, reified E: Throwable> uniffiTraitInterfaceCallWithError(
             callStatus.code = UNIFFI_CALL_ERROR
             callStatus.error_buf = lowerError(e)
         } else {
+            val err = try { e.stackTraceToString() } catch(_: Throwable) { "" }
             callStatus.code = UNIFFI_CALL_UNEXPECTED_ERROR
-            callStatus.error_buf = {{ Type::String.borrow()|lower_fn }}(e.toString())
+            callStatus.error_buf = {{ Type::String.borrow()|lower_fn }}(err)
         }
     }
 }