Suggest avoiding default case in switch statements

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

@@ -0,0 +1,57 @@
+/*
+ * (c) Copyright 2018 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.Category;
+import com.google.errorprone.BugPattern.LinkType;
+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.sun.source.tree.CaseTree;
+import com.sun.source.tree.SwitchTree;
+import java.util.Objects;
+
+@AutoService(BugChecker.class)
+@BugPattern(
+        name = "SwitchStatementDefaultCase",
+        category = Category.ONE_OFF,
+        link = "https://github.com/palantir/gradle-baseline#baseline-error-prone-checks",
+        linkType = LinkType.CUSTOM,
+        severity = SeverityLevel.SUGGESTION,
+        summary = "Avoid default cases in switch statements to correctly handle new enum variants")
+public final class SwitchStatementDefaultCase extends BugChecker implements BugChecker.SwitchTreeMatcher {
+
+    @Override
+    public Description matchSwitch(SwitchTree tree, VisitorState state) {
+        if (hasDefaultCase(tree)) {
+            return buildDescription(tree)
+                    .setMessage("Avoid using default case in switch statement.")
+                    .build();
+        }
+
+        return Description.NO_MATCH;
+    }
+
+    private boolean hasDefaultCase(SwitchTree tree) {
+        return tree.getCases().stream()
+                .map(CaseTree::getExpression)
+                .anyMatch(Objects::isNull);
+    }
+}

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

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+/*
+ * (c) Copyright 2018 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 SwitchStatementDefaultCaseTest {
+
+    private CompilationTestHelper compilationHelper;
+
+    @Before
+    public void before() {
+        compilationHelper = CompilationTestHelper.newInstance(SwitchStatementDefaultCase.class, getClass());
+    }
+
+    @Test
+    public void testDefaultCase() {
+        compilationHelper
+                .addSourceLines(
+                        "Test.java",
+                        "class Test {",
+                        "  enum Case { ONE, TWO, THREE }",
+                        "  void m(Case c) {",
+                        "    // BUG: Diagnostic contains: Avoid using default case in switch statement.",
+                        "    switch (c) {",
+                        "      case ONE:",
+                        "      case TWO:",
+                        "      case THREE:",
+                        "      default:",
+                        "        break;",
+                        "    }",
+                        "  }",
+                        "}")
+                .doTest();
+    }
+
+    @Test
+    public void testNoDefaultCase() {
+        compilationHelper
+                .addSourceLines(
+                        "Test.java",
+                        "class Test {",
+                        "  enum Case { ONE, TWO, THREE }",
+                        "  void m(Case c) {",
+                        "    switch (c) {",
+                        "      case ONE:",
+                        "      case TWO:",
+                        "      case THREE:",
+                        "        break;",
+                        "    }",
+                        "  }",
+                        "}")
+                .doTest();
+    }
+}