Add check replacing stream.sorted().findFirst() with stream.min()

baseline-error-prone/src/main/java/com/palantir/baseline/errorprone/SortedStreamFirstElement.java

@@ -0,0 +1,115 @@
+/*
+ * (c) Copyright 2023 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.
+ */
+
+package com.palantir.baseline.errorprone;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.BugPattern.SeverityLevel;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.fixes.SuggestedFix;
+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 com.sun.source.tree.Tree;
+import com.sun.tools.javac.tree.JCTree.JCMethodInvocation;
+import java.util.Comparator;
+import java.util.stream.Stream;
+
+@AutoService(BugChecker.class)
+@BugPattern(
+        link = "https://github.com/palantir/gradle-baseline#baseline-error-prone-checks",
+        linkType = BugPattern.LinkType.CUSTOM,
+        severity = SeverityLevel.SUGGESTION,
+        summary = "Using Stream::min is more efficient than finding the first element of the sorted stream. "
+                + "Stream::min performs a linear scan through the stream to find the smallest element.")
+public final class SortedStreamFirstElement extends BugChecker implements BugChecker.MethodInvocationTreeMatcher {
+
+    private static final Matcher<ExpressionTree> STREAM_FIND_FIRST_MATCHER = MethodMatchers.instanceMethod()
+            .onDescendantOf(Stream.class.getName())
+            .named("findFirst")
+            .withNoParameters();
+
+    private static final Matcher<MethodInvocationTree> RECEIVER_OF_STREAM_SORTED_NO_PARAMS_MATCHER =
+            Matchers.receiverOfInvocation(MethodMatchers.instanceMethod()
+                    .onDescendantOf(Stream.class.getName())
+                    .named("sorted")
+                    .withNoParameters());
+
+    private static final Matcher<MethodInvocationTree> RECEIVER_OF_STREAM_SORTED_WITH_COMPARATOR_MATCHER =
+            Matchers.receiverOfInvocation(MethodMatchers.instanceMethod()
+                    .onDescendantOf(Stream.class.getName())
+                    .named("sorted")
+                    .withParameters(Comparator.class.getName()));
+
+    private static final Matcher<MethodInvocationTree> MATCHER = Matchers.allOf(
+            STREAM_FIND_FIRST_MATCHER,
+            Matchers.anyOf(
+                    RECEIVER_OF_STREAM_SORTED_NO_PARAMS_MATCHER, RECEIVER_OF_STREAM_SORTED_WITH_COMPARATOR_MATCHER));
+
+    @Override
+    public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+        if (!MATCHER.matches(tree, state)) {
+            return Description.NO_MATCH;
+        }
+
+        ExpressionTree sorted = ASTHelpers.getReceiver(tree);
+        if (sorted == null) {
+            // Not expected.
+            return Description.NO_MATCH;
+        }
+        MethodInvocationTree sortedTree = (MethodInvocationTree) sorted;
+        ExpressionTree stream = ASTHelpers.getReceiver(sorted);
+        if (stream == null) {
+            // Not expected.
+            return Description.NO_MATCH;
+        }
+
+        if (RECEIVER_OF_STREAM_SORTED_NO_PARAMS_MATCHER.matches(tree, state)) {
+            return describeMatch(
+                    tree,
+                    SuggestedFix.builder()
+                            .replace(
+                                    getStartPosition(tree),
+                                    state.getEndPosition(tree),
+                                    state.getSourceForNode(stream) + ".min(Comparator.naturalOrder())")
+                            .addImport(Comparator.class.getCanonicalName())
+                            .build());
+        } else if (RECEIVER_OF_STREAM_SORTED_WITH_COMPARATOR_MATCHER.matches(tree, state)) {
+            return describeMatch(
+                    tree,
+                    SuggestedFix.builder()
+                            .replace(
+                                    getStartPosition(tree),
+                                    state.getEndPosition(tree),
+                                    state.getSourceForNode(stream) + ".min("
+                                            + state.getSourceForNode(
+                                                    sortedTree.getArguments().get(0)) + ")")
+                            .build());
+        }
+
+        return Description.NO_MATCH;
+    }
+
+    private static int getStartPosition(Tree tree) {
+        return ((JCMethodInvocation) tree).getStartPosition();
+    }
+}

baseline-error-prone/src/test/java/com/palantir/baseline/errorprone/SortedStreamFirstElementTest.java

@@ -0,0 +1,133 @@
+/*
+ * (c) Copyright 2023 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.
+ */
+
+package com.palantir.baseline.errorprone;
+
+import java.util.Comparator;
+import java.util.Optional;
+import java.util.stream.Stream;
+import org.junit.jupiter.api.Test;
+
+public class SortedStreamFirstElementTest {
+
+    @Test
+    public void test_basic() {
+        fix().addInputLines(
+                        "TestBasic.java",
+                        "import " + Optional.class.getCanonicalName() + ";",
+                        "import " + Stream.class.getCanonicalName() + ";",
+                        "class TestBasic {",
+                        "  public Optional<Integer> basic(Stream<Integer> s) {",
+                        "    return s.sorted().findFirst();",
+                        "  }",
+                        "}")
+                .addOutputLines(
+                        "TestBasic.java",
+                        "import " + Comparator.class.getCanonicalName() + ";",
+                        "import " + Optional.class.getCanonicalName() + ";",
+                        "import " + Stream.class.getCanonicalName() + ";",
+                        "class TestBasic {",
+                        "  public Optional<Integer> basic(Stream<Integer> s) {",
+                        "    return s.min(Comparator.naturalOrder());",
+                        "  }",
+                        "}")
+                .doTest();
+    }
+
+    @Test
+    public void test_comparator_already_imported() {
+        fix().addInputLines(
+                        "TestComparatorAlreadyImported.java",
+                        "import " + Comparator.class.getCanonicalName() + ";",
+                        "import " + Optional.class.getCanonicalName() + ";",
+                        "import " + Stream.class.getCanonicalName() + ";",
+                        "class TestComparatorAlreadyImported {",
+                        "  public Optional<Integer> f(Stream<Integer> s) {",
+                        "    return s.sorted().findFirst();",
+                        "  }",
+                        "  public Optional<Integer> g(Stream<Integer> s) {",
+                        "    return s.min(Comparator.naturalOrder());",
+                        "  }",
+                        "}")
+                .addOutputLines(
+                        "TestComparatorAlreadyImported.java",
+                        "import " + Comparator.class.getCanonicalName() + ";",
+                        "import " + Optional.class.getCanonicalName() + ";",
+                        "import " + Stream.class.getCanonicalName() + ";",
+                        "class TestComparatorAlreadyImported {",
+                        "  public Optional<Integer> f(Stream<Integer> s) {",
+                        "    return s.min(Comparator.naturalOrder());",
+                        "  }",
+                        "  public Optional<Integer> g(Stream<Integer> s) {",
+                        "    return s.min(Comparator.naturalOrder());",
+                        "  }",
+                        "}")
+                .doTest();
+    }
+
+    @Test
+    public void test_templated() {
+        fix().addInputLines(
+                        "TestBasic.java",
+                        "import " + Optional.class.getCanonicalName() + ";",
+                        "import " + Stream.class.getCanonicalName() + ";",
+                        "class TestBasic<T extends Comparable<? super T>> {",
+                        "  public Optional<T> basic(Stream<T> s) {",
+                        "    return s.sorted().findFirst();",
+                        "  }",
+                        "}")
+                .addOutputLines(
+                        "TestBasic.java",
+                        "import " + Comparator.class.getCanonicalName() + ";",
+                        "import " + Optional.class.getCanonicalName() + ";",
+                        "import " + Stream.class.getCanonicalName() + ";",
+                        "class TestBasic<T extends Comparable<? super T>> {",
+                        "  public Optional<T> basic(Stream<T> s) {",
+                        "    return s.min(Comparator.naturalOrder());",
+                        "  }",
+                        "}")
+                .doTest();
+    }
+
+    @Test
+    public void test_comparator() {
+        fix().addInputLines(
+                        "TestComparator.java",
+                        "import " + Comparator.class.getCanonicalName() + ";",
+                        "import " + Optional.class.getCanonicalName() + ";",
+                        "import " + Stream.class.getCanonicalName() + ";",
+                        "class TestComparator {",
+                        "  public Optional<Integer> f(Stream<Integer> s, Comparator c) {",
+                        "    return s.sorted(c).findFirst();",
+                        "  }",
+                        "}")
+                .addOutputLines(
+                        "TestComparator.java",
+                        "import " + Comparator.class.getCanonicalName() + ";",
+                        "import " + Optional.class.getCanonicalName() + ";",
+                        "import " + Stream.class.getCanonicalName() + ";",
+                        "class TestComparator {",
+                        "  public Optional<Integer> f(Stream<Integer> s, Comparator c) {",
+                        "    return s.min(c);",
+                        "  }",
+                        "}")
+                .doTest();
+    }
+
+    private RefactoringValidator fix() {
+        return RefactoringValidator.of(SortedStreamFirstElement.class, getClass());
+    }
+}

changelog/@unreleased/pr-2555.v2.yml

@@ -0,0 +1,5 @@
+type: feature
+feature:
+  description: Add check replacing `stream.sorted().findFirst()` with `stream.min()`
+  links:
+  - https://github.com/palantir/gradle-baseline/pull/2555