From 5ee07033372dae847f87be4073d88efc56c67b20 Mon Sep 17 00:00:00 2001
From: Rick Ossendrijver <rick.ossendrijver@gmail.com>
Date: Mon, 20 Feb 2023 09:09:24 +0100
Subject: [PATCH] Introduce `MonoSingleOptional` Refaster rule

---
 .../errorprone/refasterrules/ReactorRules.java      | 13 +++++++++++++
 1 file changed, 13 insertions(+)

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 c99c77482a5..85b0e69ce7f 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
@@ -717,6 +717,19 @@ Mono<Optional<T>> after(Mono<T> mono) {
     }
   }
 
+  /** Prefer {@link Mono#singleOptional()} over more contrived alternatives. */
+  static final class MonoSingleOptional<T> {
+    @BeforeTemplate
+    Mono<Optional<T>> before(Mono<T> mono) {
+      return mono.flux().collect(toOptional());
+    }
+
+    @AfterTemplate
+    Mono<Optional<T>> after(Mono<T> mono) {
+      return mono.singleOptional();
+    }
+  }
+
   /** Prefer {@link Mono#cast(Class)} over {@link Mono#map(Function)} with a cast. */
   static final class MonoCast<T, S> {
     @BeforeTemplate