From ded0a48258264f93d25e5c1b036ce76befb90ba9 Mon Sep 17 00:00:00 2001
From: Dirk van Bokkem <dirkvanbokkem@live.nl>
Date: Thu, 22 Feb 2024 09:17:14 +0100
Subject: [PATCH] Introduce `FluxFromIterable` Refaster rule (#1047)

---
 .../errorprone/refasterrules/ReactorRules.java      | 13 +++++++++++++
 .../refasterrules/ReactorRulesTestInput.java        |  4 ++++
 .../refasterrules/ReactorRulesTestOutput.java       |  4 ++++
 3 files changed, 21 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 467c526f63..57cb55a636 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
@@ -1205,6 +1205,19 @@ Flux<T> after(Flux<? extends Iterable<T>> flux, int prefetch) {
     }
   }
 
+  /** Prefer {@link Flux#fromIterable(Iterable)} over less efficient alternatives. */
+  static final class FluxFromIterable<T> {
+    @BeforeTemplate
+    Flux<T> before(Collection<T> collection) {
+      return Flux.fromStream(collection.stream());
+    }
+
+    @AfterTemplate
+    Flux<T> after(Collection<T> collection) {
+      return Flux.fromIterable(collection);
+    }
+  }
+
   /**
    * Prefer {@link Flux#count()} followed by a conversion from {@code long} to {@code int} over
    * collecting into a list and counting its elements.
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 25e0f5144e..f2f04dc3ed 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
@@ -432,6 +432,10 @@ ImmutableSet<Flux<String>> testConcatMapIterableIdentityWithPrefetch() {
         Flux.just(ImmutableList.of("bar")).concatMap(Flux::fromIterable, 2));
   }
 
+  Flux<String> testFluxFromIterable() {
+    return Flux.fromStream(ImmutableList.of("foo").stream());
+  }
+
   ImmutableSet<Mono<Integer>> testFluxCountMapMathToIntExact() {
     return ImmutableSet.of(
         Flux.just(1).collect(toImmutableList()).map(Collection::size),
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 dd25437fb6..6bfd98f972 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
@@ -427,6 +427,10 @@ ImmutableSet<Flux<String>> testConcatMapIterableIdentityWithPrefetch() {
         Flux.just(ImmutableList.of("bar")).concatMapIterable(identity(), 2));
   }
 
+  Flux<String> testFluxFromIterable() {
+    return Flux.fromIterable(ImmutableList.of("foo"));
+  }
+
   ImmutableSet<Mono<Integer>> testFluxCountMapMathToIntExact() {
     return ImmutableSet.of(
         Flux.just(1).count().map(Math::toIntExact),