Introduce Flux and Stream Refaster rules to suggest filtering bef…

…ore sorting (#393)

Fixes #386.

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

@@ -141,6 +141,22 @@ DoubleStream after(Stream<T> stream, DoubleFunction<? extends DoubleStream> func
     }
   }
 
+  /**
+   * Apply {@link DoubleStream#filter(DoublePredicate)} before {@link DoubleStream#sorted()} to
+   * reduce the number of elements to sort.
+   */
+  static final class DoubleStreamFilterSorted {
+    @BeforeTemplate
+    DoubleStream before(DoubleStream stream, DoublePredicate predicate) {
+      return stream.sorted().filter(predicate);
+    }
+
+    @AfterTemplate
+    DoubleStream after(DoubleStream stream, DoublePredicate predicate) {
+      return stream.filter(predicate).sorted();
+    }
+  }
+
   /** In order to test whether a stream has any element, simply try to find one. */
   static final class DoubleStreamIsEmpty {
     @BeforeTemplate

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

@@ -154,6 +154,22 @@ IntStream after(Stream<T> stream, IntFunction<? extends IntStream> function) {
     }
   }
 
+  /**
+   * Apply {@link IntStream#filter(IntPredicate)} before {@link IntStream#sorted()} to reduce the
+   * number of elements to sort.
+   */
+  static final class IntStreamFilterSorted {
+    @BeforeTemplate
+    IntStream before(IntStream stream, IntPredicate predicate) {
+      return stream.sorted().filter(predicate);
+    }
+
+    @AfterTemplate
+    IntStream after(IntStream stream, IntPredicate predicate) {
+      return stream.filter(predicate).sorted();
+    }
+  }
+
   /** In order to test whether a stream has any element, simply try to find one. */
   static final class IntStreamIsEmpty {
     @BeforeTemplate

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

@@ -154,6 +154,22 @@ LongStream after(Stream<T> stream, LongFunction<? extends LongStream> function)
     }
   }
 
+  /**
+   * Apply {@link LongStream#filter(LongPredicate)} before {@link LongStream#sorted()} to reduce the
+   * number of elements to sort.
+   */
+  static final class LongStreamFilterSorted {
+    @BeforeTemplate
+    LongStream before(LongStream stream, LongPredicate predicate) {
+      return stream.sorted().filter(predicate);
+    }
+
+    @AfterTemplate
+    LongStream after(LongStream stream, LongPredicate predicate) {
+      return stream.filter(predicate).sorted();
+    }
+  }
+
   /** In order to test whether a stream has any element, simply try to find one. */
   static final class LongStreamIsEmpty {
     @BeforeTemplate

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

@@ -17,6 +17,7 @@
 import com.google.errorprone.refaster.annotation.Placeholder;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.time.Duration;
+import java.util.Comparator;
 import java.util.HashMap;
 import java.util.Optional;
 import java.util.concurrent.Callable;
@@ -1062,6 +1063,38 @@ Flux<T> after(Flux<T> flux, Class<? extends Throwable> clazz, T fallbackValue) {
     }
   }
 
+  /**
+   * Apply {@link Flux#filter(Predicate)} before {@link Flux#sort()} to reduce the number of
+   * elements to sort.
+   */
+  static final class FluxFilterSort<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Predicate<? super T> predicate) {
+      return flux.sort().filter(predicate);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Predicate<? super T> predicate) {
+      return flux.filter(predicate).sort();
+    }
+  }
+
+  /**
+   * Apply {@link Flux#filter(Predicate)} before {@link Flux#sort(Comparator)} to reduce the number
+   * of elements to sort.
+   */
+  static final class FluxFilterSortWithComparator<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Predicate<? super T> predicate, Comparator<? super T> comparator) {
+      return flux.sort(comparator).filter(predicate);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Predicate<? super T> predicate, Comparator<? super T> comparator) {
+      return flux.filter(predicate).sort(comparator);
+    }
+  }
+
   /** Prefer {@link reactor.util.context.Context#empty()}} over more verbose alternatives. */
   // XXX: Consider introducing an `IsEmpty` matcher that identifies a wide range of guaranteed-empty
   // `Collection` and `Map` expressions.

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

@@ -167,6 +167,40 @@ Stream<R> after(Stream<T> stream, Function<? super S, ? extends Stream<? extends
     }
   }
 
+  /**
+   * Apply {@link Stream#filter(Predicate)} before {@link Stream#sorted()} to reduce the number of
+   * elements to sort.
+   */
+  static final class StreamFilterSorted<T> {
+    @BeforeTemplate
+    Stream<T> before(Stream<T> stream, Predicate<? super T> predicate) {
+      return stream.sorted().filter(predicate);
+    }
+
+    @AfterTemplate
+    Stream<T> after(Stream<T> stream, Predicate<? super T> predicate) {
+      return stream.filter(predicate).sorted();
+    }
+  }
+
+  /**
+   * Apply {@link Stream#filter(Predicate)} before {@link Stream#sorted(Comparator)} to reduce the
+   * number of elements to sort.
+   */
+  static final class StreamFilterSortedWithComparator<T> {
+    @BeforeTemplate
+    Stream<T> before(
+        Stream<T> stream, Predicate<? super T> predicate, Comparator<? super T> comparator) {
+      return stream.sorted(comparator).filter(predicate);
+    }
+
+    @AfterTemplate
+    Stream<T> after(
+        Stream<T> stream, Predicate<? super T> predicate, Comparator<? super T> comparator) {
+      return stream.filter(predicate).sorted(comparator);
+    }
+  }
+
   /**
    * Where possible, clarify that a mapping operation will be applied only to a single stream
    * element.

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

@@ -46,6 +46,10 @@ DoubleStream testFlatMapOuterStreamAfterFlatMapToDouble() {
     return Stream.of(1).flatMapToDouble(v -> DoubleStream.of(v * v).flatMap(DoubleStream::of));
   }
 
+  DoubleStream testDoubleStreamFilterSorted() {
+    return DoubleStream.of(1, 4, 3, 2).sorted().filter(d -> d % 2 == 0);
+  }
+
   ImmutableSet<Boolean> testDoubleStreamIsEmpty() {
     return ImmutableSet.of(
         DoubleStream.of(1).count() == 0,

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

@@ -46,6 +46,10 @@ DoubleStream testFlatMapOuterStreamAfterFlatMapToDouble() {
     return Stream.of(1).flatMapToDouble(v -> DoubleStream.of(v * v)).flatMap(DoubleStream::of);
   }
 
+  DoubleStream testDoubleStreamFilterSorted() {
+    return DoubleStream.of(1, 4, 3, 2).filter(d -> d % 2 == 0).sorted();
+  }
+
   ImmutableSet<Boolean> testDoubleStreamIsEmpty() {
     return ImmutableSet.of(
         DoubleStream.of(1).findAny().isEmpty(),

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

@@ -50,6 +50,10 @@ IntStream testFlatMapOuterStreamAfterFlatMapToInt() {
     return Stream.of(1).flatMapToInt(v -> IntStream.of(v * v).flatMap(IntStream::of));
   }
 
+  IntStream testIntStreamFilterSorted() {
+    return IntStream.of(1, 4, 3, 2).sorted().filter(i -> i % 2 == 0);
+  }
+
   ImmutableSet<Boolean> testIntStreamIsEmpty() {
     return ImmutableSet.of(
         IntStream.of(1).count() == 0,

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

@@ -50,6 +50,10 @@ IntStream testFlatMapOuterStreamAfterFlatMapToInt() {
     return Stream.of(1).flatMapToInt(v -> IntStream.of(v * v)).flatMap(IntStream::of);
   }
 
+  IntStream testIntStreamFilterSorted() {
+    return IntStream.of(1, 4, 3, 2).filter(i -> i % 2 == 0).sorted();
+  }
+
   ImmutableSet<Boolean> testIntStreamIsEmpty() {
     return ImmutableSet.of(
         IntStream.of(1).findAny().isEmpty(),

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

@@ -50,6 +50,10 @@ LongStream testFlatMapOuterStreamAfterFlatMapToLong() {
     return Stream.of(1).flatMapToLong(v -> LongStream.of(v * v).flatMap(LongStream::of));
   }
 
+  LongStream testLongStreamFilterSorted() {
+    return LongStream.of(1, 4, 3, 2).sorted().filter(l -> l % 2 == 0);
+  }
+
   ImmutableSet<Boolean> testLongStreamIsEmpty() {
     return ImmutableSet.of(
         LongStream.of(1).count() == 0,

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

@@ -50,6 +50,10 @@ LongStream testFlatMapOuterStreamAfterFlatMapToLong() {
     return Stream.of(1).flatMapToLong(v -> LongStream.of(v * v)).flatMap(LongStream::of);
   }
 
+  LongStream testLongStreamFilterSorted() {
+    return LongStream.of(1, 4, 3, 2).filter(l -> l % 2 == 0).sorted();
+  }
+
   ImmutableSet<Boolean> testLongStreamIsEmpty() {
     return ImmutableSet.of(
         LongStream.of(1).findAny().isEmpty(),

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

@@ -1,5 +1,6 @@
 package tech.picnic.errorprone.refasterrules;
 
+import static java.util.Comparator.reverseOrder;
 import static java.util.function.Function.identity;
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -327,6 +328,14 @@ Flux<Integer> testFluxOnErrorReturn() {
     return Flux.just(1).onErrorReturn(IllegalArgumentException.class::isInstance, 2);
   }
 
+  Flux<Integer> testFluxFilterSort() {
+    return Flux.just(1, 4, 3, 2).sort().filter(i -> i % 2 == 0);
+  }
+
+  Flux<Integer> testFluxFilterSortWithComparator() {
+    return Flux.just(1, 4, 3, 2).sort(reverseOrder()).filter(i -> i % 2 == 0);
+  }
+
   ImmutableSet<Context> testContextEmpty() {
     return ImmutableSet.of(Context.of(new HashMap<>()), Context.of(ImmutableMap.of()));
   }

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

@@ -1,6 +1,7 @@
 package tech.picnic.errorprone.refasterrules;
 
 import static com.google.common.collect.MoreCollectors.toOptional;
+import static java.util.Comparator.reverseOrder;
 import static java.util.function.Function.identity;
 import static org.assertj.core.api.Assertions.assertThat;
 import static reactor.function.TupleUtils.function;
@@ -322,6 +323,14 @@ Flux<Integer> testFluxOnErrorReturn() {
     return Flux.just(1).onErrorReturn(IllegalArgumentException.class, 2);
   }
 
+  Flux<Integer> testFluxFilterSort() {
+    return Flux.just(1, 4, 3, 2).filter(i -> i % 2 == 0).sort();
+  }
+
+  Flux<Integer> testFluxFilterSortWithComparator() {
+    return Flux.just(1, 4, 3, 2).filter(i -> i % 2 == 0).sort(reverseOrder());
+  }
+
   ImmutableSet<Context> testContextEmpty() {
     return ImmutableSet.of(Context.empty(), Context.empty());
   }

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

@@ -16,7 +16,7 @@
 final class StreamRulesTest implements RefasterRuleCollectionTestCase {
   @Override
   public ImmutableSet<?> elidedTypesAndStaticImports() {
-    return ImmutableSet.of(Objects.class, Streams.class, not(null), reverseOrder());
+    return ImmutableSet.of(Objects.class, Streams.class, not(null));
   }
 
   String testJoining() {
@@ -56,6 +56,14 @@ Stream<Integer> testFlatMapOuterStreamAfterFlatMap() {
     return Stream.of("foo").flatMap(v -> Stream.of(v.length()).flatMap(Stream::of));
   }
 
+  Stream<Integer> testStreamFilterSorted() {
+    return Stream.of(1, 4, 3, 2).sorted().filter(i -> i % 2 == 0);
+  }
+
+  Stream<Integer> testStreamFilterSortedWithComparator() {
+    return Stream.of(1, 4, 3, 2).sorted(reverseOrder()).filter(i -> i % 2 == 0);
+  }
+
   ImmutableSet<Optional<Integer>> testStreamMapFirst() {
     return ImmutableSet.of(
         Stream.of("foo").map(s -> s.length()).findFirst(),

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

@@ -18,7 +18,7 @@
 final class StreamRulesTest implements RefasterRuleCollectionTestCase {
   @Override
   public ImmutableSet<?> elidedTypesAndStaticImports() {
-    return ImmutableSet.of(Objects.class, Streams.class, not(null), reverseOrder());
+    return ImmutableSet.of(Objects.class, Streams.class, not(null));
   }
 
   String testJoining() {
@@ -57,6 +57,14 @@ Stream<Integer> testFlatMapOuterStreamAfterFlatMap() {
     return Stream.of("foo").flatMap(v -> Stream.of(v.length())).flatMap(Stream::of);
   }
 
+  Stream<Integer> testStreamFilterSorted() {
+    return Stream.of(1, 4, 3, 2).filter(i -> i % 2 == 0).sorted();
+  }
+
+  Stream<Integer> testStreamFilterSortedWithComparator() {
+    return Stream.of(1, 4, 3, 2).filter(i -> i % 2 == 0).sorted(reverseOrder());
+  }
+
   ImmutableSet<Optional<Integer>> testStreamMapFirst() {
     return ImmutableSet.of(
         Stream.of("foo").findFirst().map(s -> s.length()),