Prefer Streams#concat over contrived alternative

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

@@ -27,6 +27,7 @@
 import com.google.errorprone.refaster.annotation.MayOptionallyUse;
 import com.google.errorprone.refaster.annotation.NotMatches;
 import com.google.errorprone.refaster.annotation.Placeholder;
+import com.google.errorprone.refaster.annotation.Repeated;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.util.Arrays;
 import java.util.Collection;
@@ -635,4 +636,16 @@ Stream<T> after(Stream<T> s1, Stream<T> s2) {
       return Stream.concat(s1, s2);
     }
   }
+
+  static final class StreamsConcat<T> {
+    @BeforeTemplate
+    Stream<T> before(@Repeated Stream<T> stream) {
+      return Stream.of(Refaster.asVarargs(stream)).flatMap(Function.identity());
+    }
+
+    @AfterTemplate
+    Stream<T> after(@Repeated Stream<T> stream) {
+      return Streams.concat(Refaster.asVarargs(stream));
+    }
+  }
 }

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

@@ -254,4 +254,9 @@ ImmutableSet<Integer> testStreamFlatMapCollect() {
   Stream<Integer> testStreamConcat() {
     return Stream.of(Stream.of(1), Stream.of(2)).flatMap(Function.identity());
   }
+
+  Stream<Integer> testStreamsConcat() {
+    return Stream.of(Stream.of(1), Stream.of(2), Stream.of(3), Stream.of(4))
+        .flatMap(Function.identity());
+  }
 }

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

@@ -255,4 +255,8 @@ ImmutableSet<Integer> testStreamFlatMapCollect() {
   Stream<Integer> testStreamConcat() {
     return Stream.concat(Stream.of(1), Stream.of(2));
   }
+
+  Stream<Integer> testStreamsConcat() {
+    return Streams.concat(Stream.of(1), Stream.of(2), Stream.of(3), Stream.of(4));
+  }
 }