Refaster rule to remove unnecessary supplier creation (#1059)

Refaster rule to remove unnecessary supplier creation

baseline-refaster-rules/src/main/java/com/palantir/baseline/refaster/SupplierRedefinition.java

@@ -0,0 +1,42 @@
+/*
+ * (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.refaster;
+
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import java.util.function.Supplier;
+
+/** No reason to redefine a supplier when the target type is also a supplier. */
+final class SupplierRedefinition<T> {
+
+    @BeforeTemplate
+    @SuppressWarnings({"Convert2MethodRef", "FunctionalExpressionCanBeFolded"})
+    Supplier<T> before1(Supplier<T> input) {
+        return () -> input.get();
+    }
+
+    @BeforeTemplate
+    @SuppressWarnings("FunctionalExpressionCanBeFolded")
+    Supplier<T> before2(Supplier<T> input) {
+        return input::get;
+    }
+
+    @AfterTemplate
+    Supplier<T> after(Supplier<T> input) {
+        return input;
+    }
+}

baseline-refaster-rules/src/test/java/com/palantir/baseline/refaster/SupplierRedefinitionTest.java

@@ -0,0 +1,51 @@
+/*
+ * (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.refaster;
+
+import org.junit.Test;
+
+public class SupplierRedefinitionTest {
+
+    @Test
+    public void test() {
+        RefasterTestHelper
+                .forRefactoring(SupplierRedefinition.class)
+                .withInputLines(
+                        "Test",
+                        "import java.util.*;",
+                        "import java.util.function.*;",
+                        "class Test {",
+                        "  String func1(Optional<String> in, Supplier<String> defaultValue) {",
+                        "    return in.orElseGet(() -> defaultValue.get());",
+                        "  }",
+                        "  String func2(Optional<String> in, Supplier<String> defaultValue) {",
+                        "    return in.orElseGet(defaultValue::get);",
+                        "  }",
+                        "}")
+                .hasOutputLines(
+                        "import java.util.*;",
+                        "import java.util.function.*;",
+                        "class Test {",
+                        "  String func1(Optional<String> in, Supplier<String> defaultValue) {",
+                        "    return in.orElseGet(defaultValue);",
+                        "  }",
+                        "  String func2(Optional<String> in, Supplier<String> defaultValue) {",
+                        "    return in.orElseGet(defaultValue);",
+                        "  }",
+                        "}");
+    }
+}

changelog/@unreleased/pr-1059.v2.yml

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+type: improvement
+improvement:
+  description: Refaster rule to remove unnecessary supplier creation
+  links:
+  - https://github.com/palantir/gradle-baseline/pull/1059