From 81ffd04fe4fb88267d8f9c99f99f98668d42508b Mon Sep 17 00:00:00 2001
From: Phil Werli <phil.werli@teampicnic.com>
Date: Thu, 19 Jan 2023 13:49:57 +0100
Subject: [PATCH] Extend `MonoIdentity` Refaster rule (#470)

By flagging expressions of the form `mono.flux().singleOrEmpty()`.
---
 .../tech/picnic/errorprone/refasterrules/ReactorRules.java     | 3 ++-
 .../picnic/errorprone/refasterrules/ReactorRulesTestInput.java | 1 +
 .../errorprone/refasterrules/ReactorRulesTestOutput.java       | 2 +-
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ReactorRules.java b/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ReactorRules.java
index b4cd081f1b..6c49792fb8 100644
--- a/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ReactorRules.java
+++ b/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ReactorRules.java
@@ -369,7 +369,8 @@ Flux<T> after(Flux<T> flux, T object) {
   static final class MonoIdentity<T> {
     @BeforeTemplate
     Mono<T> before(Mono<T> mono) {
-      return Refaster.anyOf(mono.switchIfEmpty(Mono.empty()), mono.flux().next());
+      return Refaster.anyOf(
+          mono.switchIfEmpty(Mono.empty()), mono.flux().next(), mono.flux().singleOrEmpty());
     }
 
     @BeforeTemplate
diff --git a/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ReactorRulesTestInput.java b/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ReactorRulesTestInput.java
index 3377b40e25..25596c5cc3 100644
--- a/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ReactorRulesTestInput.java
+++ b/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ReactorRulesTestInput.java
@@ -119,6 +119,7 @@ ImmutableSet<Mono<?>> testMonoIdentity() {
     return ImmutableSet.of(
         Mono.just(1).switchIfEmpty(Mono.empty()),
         Mono.just(2).flux().next(),
+        Mono.just(3).flux().singleOrEmpty(),
         Mono.<Void>empty().then());
   }
 
diff --git a/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ReactorRulesTestOutput.java b/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ReactorRulesTestOutput.java
index e5bee9e4e5..7c471e5314 100644
--- a/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ReactorRulesTestOutput.java
+++ b/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ReactorRulesTestOutput.java
@@ -121,7 +121,7 @@ ImmutableSet<Flux<String>> testFluxDefaultIfEmpty() {
   }
 
   ImmutableSet<Mono<?>> testMonoIdentity() {
-    return ImmutableSet.of(Mono.just(1), Mono.just(2), Mono.<Void>empty());
+    return ImmutableSet.of(Mono.just(1), Mono.just(2), Mono.just(3), Mono.<Void>empty());
   }
 
   ImmutableSet<Flux<Integer>> testFluxSwitchIfEmptyOfEmptyPublisher() {