Fix #656 DangerousStringInternUsage: Disallow String.intern() invocations

README.md

@@ -162,6 +162,7 @@ Safe Logging can be found at [github.com/palantir/safe-logging](https://github.c
 - `JUnit5RuleUsage`: Prevent accidental usage of `org.junit.Rule`/`org.junit.ClassRule` within Junit5 tests
 - `DangerousCompletableFutureUsage`: Disallow CompletableFuture asynchronous operations without an Executor.
 - `NonComparableStreamSort`: Stream.sorted() should only be called on streams of Comparable types.
+- `DangerousStringInternUsage`: Disallow String.intern() invocations in favor of more predictable, scalable alternatives.
 
 ## com.palantir.baseline-checkstyle
 Checkstyle rules can be suppressed on a per-line or per-block basis. (It is good practice to first consider formatting

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

@@ -0,0 +1,69 @@
+/*
+ * (c) Copyright 2019 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.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.matchers.method.MethodMatchers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+
+@AutoService(BugChecker.class)
+@BugPattern(
+        name = "DangerousStringInternUsage",
+        severity = SeverityLevel.WARNING,
+        summary = "Disallow String.intern() invocations.")
+public final class DangerousStringInternUsage extends BugChecker implements BugChecker.MethodInvocationTreeMatcher {
+    private static final String MESSAGE = "Should not use String.intern(). "
+            + "Java string intern is complex and unpredictable. In most cases intern performs worse than pure-java "
+            + "implementations such as Guava Interners "
+            + "(https://guava.dev/releases/27.0.1-jre/api/docs/com/google/common/collect/Interners.html). If you are "
+            + "confident that String.intern is the correct tool, please make sure you fully understand the "
+            + "consequences."
+            + "\nFrom https://shipilev.net/jvm/anatomy-quarks/10-string-intern/"
+            + "\n> For OpenJDK, String.intern() is the gateway to native JVM String table, and it comes with"
+            + "\n> caveats: throughput, memory footprint, pause time problems will await the users. It is very"
+            + "\n> easy to underestimate the impact of these caveats. Hand-rolled deduplicators/interners are working"
+            + "\n> much more reliably, because they are working on Java side, are just the regular Java objects,"
+            + "\n> generally better sized/resized, and also can be thrown away completely when not needed anymore."
+            + "\n> GC-assisted String deduplication does alleviate things even more."
+            + "\n> In almost every project we were taking care of, removing String.intern() from the hotpaths, "
+            + "\n> or optionally replacing it with a handrolled deduplicator, was the very profitable performance"
+            + "\n> optimization. Do not use String.intern() without thinking very hard about it, okay?";
+    private static final long serialVersionUID = 1L;
+
+    private static final Matcher<ExpressionTree> STRING_INTERN_METHOD_MATCHER =
+            MethodMatchers.instanceMethod()
+                    .onExactClass(String.class.getName())
+                    .named("intern")
+                    .withParameters();
+
+    @Override
+    public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+        if (STRING_INTERN_METHOD_MATCHER.matches(tree, state)) {
+            return buildDescription(tree)
+                    .setMessage(MESSAGE)
+                    .build();
+        }
+        return Description.NO_MATCH;
+    }
+}

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

@@ -0,0 +1,44 @@
+/*
+ * (c) Copyright 2019 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.errorprone.CompilationTestHelper;
+import org.junit.Before;
+import org.junit.Test;
+
+public class DangerousStringInternUsageTest {
+
+    private CompilationTestHelper compilationHelper;
+
+    @Before
+    public void before() {
+        compilationHelper = CompilationTestHelper.newInstance(DangerousStringInternUsage.class, getClass());
+    }
+
+    @Test
+    public void should_warn_when_parallel_with_no_arguments_is_invoked_on_subclass_of_java_stream() {
+        compilationHelper.addSourceLines(
+                "Test.java",
+                "class Test {",
+                "   String f() {",
+                "       // BUG: Diagnostic contains: Should not use String.intern().",
+                "       return getClass().getName().intern();",
+                "   }",
+                "}"
+        ).doTest();
+    }
+}

changelog/@unreleased/pr-754.v2.yml

@@ -0,0 +1,5 @@
+type: improvement
+improvement:
+  description: '`DangerousStringInternUsage`: Disallow String.intern() invocations'
+  links:
+  - https://github.com/palantir/gradle-baseline/pull/754