From 36e8e07cbe530b0296a8af71050e8d35c4251f48 Mon Sep 17 00:00:00 2001
From: Brendan Long <self@brendanlong.com>
Date: Sat, 4 Nov 2017 12:06:25 -0400
Subject: Keep the original exception in Future.map/flat_map

If a chain of maps fails, the final `exception` should be the actual
exception, not a semi-useless `FutureError.EXCEPTION`.

Fixes https://gitlab.gnome.org/GNOME/libgee/issues/23
---
 gee/future.vala | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/gee/future.vala b/gee/future.vala
index 654041b..9a004b2 100644
--- a/gee/future.vala
+++ b/gee/future.vala
@@ -134,6 +134,8 @@ public interface Gee.Future<G> : Object {
 		wait_async.begin ((obj, res) => {
 			try {
 				promise.set_value (func (wait_async.end (res)));
+			} catch (FutureError.EXCEPTION e) {
+				promise.set_exception (this.exception);
 			} catch (Error ex) {
 				promise.set_exception ((owned)ex);
 			}
@@ -234,8 +236,15 @@ public interface Gee.Future<G> : Object {
 	private static async void do_flat_map<A, B> (owned FlatMapFunc<B, A> func, Future<A> future, Promise<B> promise) {
 		try {
 			A input = yield future.wait_async ();
-			B output = yield func (input).wait_async ();
-			promise.set_value ((owned)output);
+			Future<B> output_future = func (input);
+			try {
+				B output = yield output_future.wait_async ();
+				promise.set_value ((owned)output);
+			} catch (FutureError.EXCEPTION e) {
+				promise.set_exception (output_future.exception);
+			}
+		} catch (FutureError.EXCEPTION e) {
+			promise.set_exception (future.exception);
 		} catch (Error ex) {
 			promise.set_exception ((owned)ex);
 		}
-- 
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