[improvement] Ensure Optional#orElse argument is not method invocation

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

@@ -0,0 +1,73 @@
+/*
+ * (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.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+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.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.source.tree.Tree;
+
+@AutoService(BugChecker.class)
+@BugPattern(
+        name = "OptionalOrElseMethodInvocation",
+        link = "https://github.com/palantir/gradle-baseline#baseline-error-prone-checks",
+        linkType = BugPattern.LinkType.CUSTOM,
+        severity = SeverityLevel.ERROR,
+        summary = "Expression passed to Optional#orElse invokes a method, use Optional#orElseGet instead")
+public final class OptionalOrElseMethodInvocation extends BugChecker implements MethodInvocationTreeMatcher {
+
+    private static final long serialVersionUID = 1L;
+
+    private static final Matcher<ExpressionTree> OR_ELSE_METHOD = MethodMatchers.instanceMethod()
+            .onExactClass("java.util.Optional")
+            .named("orElse");
+
+    private static final Matcher<Tree> METHOD_INVOCATIONS =
+            Matchers.contains(ExpressionTree.class, MethodMatchers.anyMethod());
+
+    @Override
+    public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+        if (!OR_ELSE_METHOD.matches(tree, state)) {
+            return Description.NO_MATCH;
+        }
+
+        ExpressionTree orElseArg = tree.getArguments().get(0);
+
+        if (!METHOD_INVOCATIONS.matches(orElseArg, state)) {
+            return Description.NO_MATCH;
+        }
+
+        return buildDescription(tree)
+                .setMessage("Expression passed to Optional#orElse invokes a method")
+                .addFix(SuggestedFix.builder()
+                        .postfixWith(tree.getMethodSelect(), "Get")
+                        .prefixWith(orElseArg, "() -> ")
+                        .build())
+                .build();
+    }
+
+}

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

@@ -0,0 +1,98 @@
+/*
+ * (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.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.Before;
+import org.junit.Test;
+
+public final class OptionalOrElseMethodInvocationTests {
+
+    private CompilationTestHelper compilationHelper;
+    private BugCheckerRefactoringTestHelper refactoringTestHelper;
+
+    @Before
+    public void before() {
+        compilationHelper = CompilationTestHelper.newInstance(OptionalOrElseMethodInvocation.class, getClass());
+        refactoringTestHelper = BugCheckerRefactoringTestHelper.newInstance(
+                new OptionalOrElseMethodInvocation(), getClass());
+    }
+
+    private void test(String expr) {
+        compilationHelper
+                .addSourceLines(
+                        "Test.java",
+                        "import java.util.Optional;",
+                        "class Test {",
+                        "  String f() { return \"hello\"; }",
+                        "  String s = \"world\";",
+                        "  // BUG: Diagnostic contains: invokes a method",
+                        "  private final String string = Optional.of(\"hello\").orElse(" + expr + ");",
+                        "}")
+                .doTest();
+    }
+
+    @Test
+    public void testNonCompileTimeConstantExpression() {
+        test("f()");
+        test("s + s");
+        test("\"world\" + s");
+        test("\"world\".substring(1)");
+    }
+
+    @Test
+    public void testNonCompileTimeConstantExpression_replacement() {
+        refactoringTestHelper
+                .addInputLines(
+                        "Test.java",
+                        "import java.util.Optional;",
+                        "class Test {",
+                        "  String f() { return \"hello\"; }",
+                        "  private final String string = Optional.of(\"hello\").orElse(f());",
+                        "}")
+                .addOutputLines(
+                        "Test.java",
+                        "import java.util.Optional;",
+                        "class Test {",
+                        "  String f() { return \"hello\"; }",
+                        "  private final String string = Optional.of(\"hello\").orElseGet(() -> f());",
+                        "}")
+                .doTest(BugCheckerRefactoringTestHelper.TestMode.TEXT_MATCH);
+    }
+
+    @Test
+    public void negative() {
+        compilationHelper
+                .addSourceLines(
+                        "Test.java",
+                        "import java.util.Optional;",
+                        "class Test {",
+                        "  private static final String compileTimeConstant = \"constant\";",
+                        "  String f() { return \"hello\"; }",
+                        "  void test() {",
+                        "    Optional.of(\"hello\").orElse(\"constant\");",
+                        "    Optional.of(\"hello\").orElse(compileTimeConstant);",
+                        "    String string = f();",
+                        "    Optional.of(\"hello\").orElse(string);",
+                        "    Optional.of(\"hello\").orElseGet(() -> f());",
+                        "  }",
+                        "}")
+                .doTest();
+    }
+
+}