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Add StreamFlatMapOptional error-prone check #2946
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79 changes: 79 additions & 0 deletions
79
...ine-error-prone/src/main/java/com/palantir/baseline/errorprone/StreamFlatMapOptional.java
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/* | ||
* (c) Copyright 2024 Palantir Technologies Inc. All rights reserved. | ||
* | ||
* Licensed under the Apache License, Version 2.0 (the "License"); | ||
* you may not use this file except in compliance with the License. | ||
* You may obtain a copy of the License at | ||
* | ||
* http://www.apache.org/licenses/LICENSE-2.0 | ||
* | ||
* Unless required by applicable law or agreed to in writing, software | ||
* distributed under the License is distributed on an "AS IS" BASIS, | ||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
* See the License for the specific language governing permissions and | ||
* limitations under the License. | ||
*/ | ||
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package com.palantir.baseline.errorprone; | ||
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import com.google.auto.service.AutoService; | ||
import com.google.errorprone.BugPattern; | ||
import com.google.errorprone.VisitorState; | ||
import com.google.errorprone.bugpatterns.BugChecker; | ||
import com.google.errorprone.fixes.SuggestedFix; | ||
import com.google.errorprone.fixes.SuggestedFixes; | ||
import com.google.errorprone.matchers.ChildMultiMatcher.MatchType; | ||
import com.google.errorprone.matchers.Description; | ||
import com.google.errorprone.matchers.Matcher; | ||
import com.google.errorprone.matchers.Matchers; | ||
import com.google.errorprone.matchers.method.MethodMatchers; | ||
import com.google.errorprone.util.ASTHelpers; | ||
import com.sun.source.tree.ExpressionTree; | ||
import com.sun.source.tree.MethodInvocationTree; | ||
import java.util.Optional; | ||
import java.util.function.Function; | ||
import java.util.stream.Stream; | ||
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@AutoService(BugChecker.class) | ||
@BugPattern( | ||
link = "https://github.com/palantir/gradle-baseline#baseline-error-prone-checks", | ||
linkType = BugPattern.LinkType.CUSTOM, | ||
severity = BugPattern.SeverityLevel.WARNING, | ||
summary = "`Stream.filter(Optional::isPresent).map(Optional::get)` is more efficient than " | ||
+ "`Stream.flatMap(Optional::stream)`") | ||
public final class StreamFlatMapOptional extends BugChecker implements BugChecker.MethodInvocationTreeMatcher { | ||
private static final long serialVersionUID = 1L; | ||
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private static final Matcher<ExpressionTree> STREAM_FLAT_MAP = MethodMatchers.instanceMethod() | ||
.onDescendantOf(Stream.class.getName()) | ||
.namedAnyOf("flatMap") | ||
.withParameters(Function.class.getName()); | ||
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private static final Matcher<ExpressionTree> OPTIONAL_STREAM = MethodMatchers.instanceMethod() | ||
.onDescendantOf(Optional.class.getName()) | ||
.named("stream") | ||
.withNoParameters(); | ||
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private static final Matcher<ExpressionTree> STREAM_FLATMAP_OPTIONAL_STREAM = Matchers.methodInvocation( | ||
STREAM_FLAT_MAP, | ||
// Any of the three MatchTypes are reasonable in this case, given a single arg | ||
MatchType.LAST, | ||
OPTIONAL_STREAM); | ||
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@Override | ||
public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) { | ||
if (STREAM_FLATMAP_OPTIONAL_STREAM.matches(tree, state)) { | ||
ExpressionTree receiver = ASTHelpers.getReceiver(tree.getMethodSelect()); | ||
if (receiver != null) { | ||
SuggestedFix.Builder fix = SuggestedFix.builder(); | ||
String optionalType = SuggestedFixes.qualifyType(state, fix, Optional.class.getCanonicalName()); | ||
String replacement = ".filter(" + optionalType + "::isPresent).map(" + optionalType + "::get)"; | ||
return buildDescription(tree) | ||
.addFix(fix.replace(state.getEndPosition(receiver), state.getEndPosition(tree), replacement) | ||
.build()) | ||
.build(); | ||
} | ||
} | ||
return Description.NO_MATCH; | ||
} | ||
} |
72 changes: 72 additions & 0 deletions
72
...error-prone/src/test/java/com/palantir/baseline/errorprone/StreamFlatmapOptionalTest.java
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/* | ||
* (c) Copyright 2024 Palantir Technologies Inc. All rights reserved. | ||
* | ||
* Licensed under the Apache License, Version 2.0 (the "License"); | ||
* you may not use this file except in compliance with the License. | ||
* You may obtain a copy of the License at | ||
* | ||
* http://www.apache.org/licenses/LICENSE-2.0 | ||
* | ||
* Unless required by applicable law or agreed to in writing, software | ||
* distributed under the License is distributed on an "AS IS" BASIS, | ||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
* See the License for the specific language governing permissions and | ||
* limitations under the License. | ||
*/ | ||
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package com.palantir.baseline.errorprone; | ||
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import org.junit.jupiter.api.Test; | ||
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class StreamFlatmapOptionalTest { | ||
@Test | ||
public void test() { | ||
fix().addInputLines( | ||
"Test.java", | ||
"import java.util.Collection;", | ||
"import java.util.Optional;", | ||
"import java.util.stream.Stream;", | ||
"public class Test {", | ||
" Stream<String> f1(Stream<Collection<Optional<String>>> in) {", | ||
" return in.flatMap(Collection::stream).flatMap(Optional::stream);", | ||
" }", | ||
" Stream<String> f2(Stream<Collection<Optional<String>>> in) {", | ||
" return in.flatMap(list -> list.stream().flatMap(Optional::stream));", | ||
" }", | ||
" Stream<String> f3(Stream<Collection<Optional<String>>> in) {", | ||
" return in.flatMap(list -> list.stream()).flatMap(Optional::stream);", | ||
" }", | ||
" Stream<String> f4(Stream<Optional<Optional<String>>> in) {", | ||
" return in.flatMap(Optional::stream).flatMap(Optional::stream);", | ||
" }", | ||
"}") | ||
.addOutputLines( | ||
"Test.java", | ||
"import java.util.Collection;", | ||
"import java.util.Optional;", | ||
"import java.util.stream.Stream;", | ||
"public class Test {", | ||
" Stream<String> f1(Stream<Collection<Optional<String>>> in) {", | ||
" return in.flatMap(Collection::stream)" | ||
+ ".filter(Optional::isPresent).map(Optional::get);", | ||
" }", | ||
" Stream<String> f2(Stream<Collection<Optional<String>>> in) {", | ||
" return in.flatMap(list -> list.stream()" | ||
+ ".filter(Optional::isPresent).map(Optional::get));", | ||
" }", | ||
" Stream<String> f3(Stream<Collection<Optional<String>>> in) {", | ||
" return in.flatMap(list -> list.stream())" | ||
+ ".filter(Optional::isPresent).map(Optional::get);", | ||
" }", | ||
" Stream<String> f4(Stream<Optional<Optional<String>>> in) {", | ||
" return in.filter(Optional::isPresent).map(Optional::get)" | ||
+ ".filter(Optional::isPresent).map(Optional::get);", | ||
" }", | ||
"}") | ||
.doTest(); | ||
} | ||
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private RefactoringValidator fix() { | ||
return RefactoringValidator.of(StreamFlatMapOptional.class, getClass()); | ||
} | ||
} |
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type: improvement | ||
improvement: | ||
description: |- | ||
If one has a `Stream<Optional<T>> stream` of size `N` and does `stream.flatMap(Optional::stream)`, you’ll end up allocating `N` extra streams — one for each `Optional` input element. When `N` is large, those allocations can cause extra GC cycles and pauses if allocation rate is high enough leading to issues with latency, throughput, and allocation sensitive code paths. | ||
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`Stream.filter(Optional::isPresent).map(Optional::get)` is more efficient than `Stream.flatMap(Optional::stream)` as it does not allocate a new `Stream` for every element in the stream. | ||
links: | ||
- https://github.com/palantir/gradle-baseline/pull/2946 |
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Should we use
orElseThrow
instead ofget
? The Java docs state thatorElseThrow
should be preferred and I've come to agree with this recommendation.https://docs.oracle.com/javase/10/docs/api/java/util/Optional.html#get()
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Good call #2950