Handle failures in the block passed to Promise#flat_map

Author: obrok

lib/concurrent/promise.rb

@@ -126,10 +126,14 @@ def flat_map(&block)
 
       on_error { |e| child.on_reject(e) }
       on_success do |result1|
-        inner = block.call(result1)
-        inner.execute
-        inner.on_success { |result2| child.on_fulfill(result2) }
-        inner.on_error { |e| child.on_reject(e) }
+        begin
+          inner = block.call(result1)
+          inner.execute
+          inner.on_success { |result2| child.on_fulfill(result2) }
+          inner.on_error { |e| child.on_reject(e) }
+        rescue => e
+          child.on_reject(e)
+        end
       end
 
       child

spec/concurrent/promise_spec.rb

@@ -289,6 +289,12 @@ module Concurrent
         expect(child).to be_rejected
       end
 
+      it 'fails if the generating block fails' do
+        child = Promise.new(executor: executor) { }.flat_map { fail }.execute.wait
+
+        expect(child).to be_rejected
+      end
+
     end
 
     describe '#zip' do