From ee5e33eb9910edf8d86d7e510b38c461741444f6 Mon Sep 17 00:00:00 2001
From: Benedek Halasi <t0h3ow7t2@mozmail.com>
Date: Fri, 20 Jan 2023 13:32:39 +0100
Subject: [PATCH] Introduce `Flux.to{Stream,Iterable}` Refaster rules fixes
 #468

---
 .../refasterrules/ReactorRules.java           | 33 +++++++++++++++++++
 .../refasterrules/ReactorRulesTestInput.java  | 12 ++++++-
 .../refasterrules/ReactorRulesTestOutput.java | 12 ++++++-
 3 files changed, 55 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 c99c77482a..ed3700d421 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
@@ -4,6 +4,7 @@
 import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
 import static java.util.function.Function.identity;
+import static java.util.stream.Collectors.toList;
 import static org.assertj.core.api.Assertions.assertThat;
 import static reactor.function.TupleUtils.function;
 
@@ -27,6 +28,7 @@
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
+import java.util.stream.Stream;
 import org.jspecify.annotations.Nullable;
 import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
@@ -1303,4 +1305,35 @@ Duration after(StepVerifier.LastStep step, Duration duration) {
       return step.verifyTimeout(duration);
     }
   }
+
+  /** Avoid accidental blocking with {@link Flux#toStream()} */
+  // XXX: The alternative may lose some performance due to
+  // buffering and prefetching
+  static final class FluxToStream<T> {
+
+    @BeforeTemplate
+    Stream<T> before(Flux<T> flux) {
+      return flux.toStream();
+    }
+
+    @AfterTemplate
+    Stream<T> after(Flux<T> flux) {
+      return flux.collect(toList()).block().stream();
+    }
+  }
+
+  /** Avoid accidental blocking with {@link Flux#toIterable()} */
+  // XXX: The alternative may lose some performance due to buffering and prefetching
+  static final class FluxToIterable<T> {
+
+    @BeforeTemplate
+    Iterable<T> before(Flux<T> flux) {
+      return flux.toIterable();
+    }
+
+    @AfterTemplate
+    Iterable<T> after(Flux<T> flux) {
+      return flux.collect(toList()).block();
+    }
+  }
 }
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 25596c5cc3..16c3f9f198 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
@@ -12,6 +12,8 @@
 import java.util.Optional;
 import java.util.concurrent.Callable;
 import java.util.function.Supplier;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
@@ -23,7 +25,7 @@
 final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
   @Override
   public ImmutableSet<?> elidedTypesAndStaticImports() {
-    return ImmutableSet.of(assertThat(0), HashMap.class, ImmutableMap.class);
+    return ImmutableSet.of(assertThat(0), Collectors.class, HashMap.class, ImmutableMap.class);
   }
 
   ImmutableSet<Mono<?>> testMonoFromSupplier() {
@@ -402,4 +404,12 @@ Duration testStepVerifierLastStepVerifyErrorMessage() {
   Duration testStepVerifierLastStepVerifyTimeout() {
     return StepVerifier.create(Mono.empty()).expectTimeout(Duration.ZERO).verify();
   }
+
+  Stream<Integer> testFluxToStream() {
+    return Flux.just(1, 2, 3).toStream();
+  }
+
+  Iterable<Integer> testFluxToIterable() {
+    return Flux.just(1, 2, 3).toIterable();
+  }
 }
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 7c471e5314..679a27e1d7 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
@@ -14,6 +14,8 @@
 import java.util.Optional;
 import java.util.concurrent.Callable;
 import java.util.function.Supplier;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.function.TupleUtils;
@@ -26,7 +28,7 @@
 final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
   @Override
   public ImmutableSet<?> elidedTypesAndStaticImports() {
-    return ImmutableSet.of(assertThat(0), HashMap.class, ImmutableMap.class);
+    return ImmutableSet.of(assertThat(0), Collectors.class, HashMap.class, ImmutableMap.class);
   }
 
   ImmutableSet<Mono<?>> testMonoFromSupplier() {
@@ -391,4 +393,12 @@ Duration testStepVerifierLastStepVerifyErrorMessage() {
   Duration testStepVerifierLastStepVerifyTimeout() {
     return StepVerifier.create(Mono.empty()).verifyTimeout(Duration.ZERO);
   }
+
+  Stream<Integer> testFluxToStream() {
+    return Flux.just(1, 2, 3).collect(Collectors.toList()).block().stream();
+  }
+
+  Iterable<Integer> testFluxToIterable() {
+    return Flux.just(1, 2, 3).collect(Collectors.toList()).block();
+  }
 }