Introduce MonoFromFutureAsyncLoadingCacheGet Refaster rule (#1290)

error-prone-contrib/pom.xml

@@ -67,6 +67,11 @@
             <artifactId>jackson-annotations</artifactId>
             <scope>provided</scope>
         </dependency>
+        <dependency>
+            <groupId>com.github.ben-manes.caffeine</groupId>
+            <artifactId>caffeine</artifactId>
+            <scope>provided</scope>
+        </dependency>
         <dependency>
             <groupId>com.google.auto.service</groupId>
             <artifactId>auto-service-annotations</artifactId>

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ReactorRules.java

@@ -13,6 +13,7 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static reactor.function.TupleUtils.function;
 
+import com.github.benmanes.caffeine.cache.AsyncLoadingCache;
 import com.google.common.collect.ImmutableCollection;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
@@ -1956,6 +1957,22 @@ Mono<T> after(CompletableFuture<T> future, boolean suppressCancel) {
     }
   }
 
+  /**
+   * Don't propagate {@link Mono} cancellations to an upstream cache value computation, as
+   * completion of such computations may benefit concurrent or subsequent cache usages.
+   */
+  static final class MonoFromFutureAsyncLoadingCacheGet<K, V> {
+    @BeforeTemplate
+    Mono<V> before(AsyncLoadingCache<K, V> cache, K key) {
+      return Mono.fromFuture(() -> cache.get(key));
+    }
+
+    @AfterTemplate
+    Mono<V> after(AsyncLoadingCache<K, V> cache, K key) {
+      return Mono.fromFuture(() -> cache.get(key), /* suppressCancel= */ true);
+    }
+  }
+
   /**
    * Prefer {@link Flux#fromStream(Supplier)} over {@link Flux#fromStream(Stream)}, as the former
    * yields a {@link Flux} that is more likely to behave as expected when subscribed to more than

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ReactorRulesTestInput.java

@@ -10,6 +10,7 @@
 import static java.util.stream.Collectors.toCollection;
 import static org.assertj.core.api.Assertions.assertThat;
 
+import com.github.benmanes.caffeine.cache.AsyncLoadingCache;
 import com.google.common.collect.ImmutableCollection;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
@@ -664,6 +665,10 @@ Mono<Void> testMonoFromFutureSupplierBoolean() {
     return Mono.fromFuture(CompletableFuture.completedFuture(null), true);
   }
 
+  Mono<String> testMonoFromFutureAsyncLoadingCacheGet() {
+    return Mono.fromFuture(() -> ((AsyncLoadingCache<Integer, String>) null).get(0));
+  }
+
   Flux<Integer> testFluxFromStreamSupplier() {
     return Flux.fromStream(Stream.of(1));
   }

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ReactorRulesTestOutput.java

@@ -12,6 +12,7 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static reactor.function.TupleUtils.function;
 
+import com.github.benmanes.caffeine.cache.AsyncLoadingCache;
 import com.google.common.collect.ImmutableCollection;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
@@ -644,6 +645,10 @@ Mono<Void> testMonoFromFutureSupplierBoolean() {
     return Mono.fromFuture(() -> CompletableFuture.completedFuture(null), true);
   }
 
+  Mono<String> testMonoFromFutureAsyncLoadingCacheGet() {
+    return Mono.fromFuture(() -> ((AsyncLoadingCache<Integer, String>) null).get(0), true);
+  }
+
   Flux<Integer> testFluxFromStreamSupplier() {
     return Flux.fromStream(() -> Stream.of(1));
   }

pom.xml

@@ -300,6 +300,11 @@
                 <type>pom</type>
                 <scope>import</scope>
             </dependency>
+            <dependency>
+                <groupId>com.github.ben-manes.caffeine</groupId>
+                <artifactId>caffeine</artifactId>
+                <version>3.1.8</version>
+            </dependency>
             <dependency>
                 <groupId>com.google.auto</groupId>
                 <artifactId>auto-common</artifactId>