From 658fbcbdfd2b16f8c014e8d5d6238d1c2a332231 Mon Sep 17 00:00:00 2001
From: Stephan Schroevers <stephan.schroevers@teampicnic.com>
Date: Wed, 4 Oct 2023 21:39:37 +0200
Subject: [PATCH] Introduce `ClassRules` Refaster rule collection

---
 .../errorprone/refasterrules/ClassRules.java  | 65 +++++++++++++++++++
 .../refasterrules/ClassRulesTestInput.java    | 25 +++++++
 .../refasterrules/ClassRulesTestOutput.java   | 25 +++++++
 3 files changed, 115 insertions(+)
 create mode 100644 error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ClassRules.java
 create mode 100644 error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ClassRulesTestInput.java
 create mode 100644 error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ClassRulesTestOutput.java

diff --git a/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ClassRules.java b/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ClassRules.java
new file mode 100644
index 00000000000..2890dd1b9f4
--- /dev/null
+++ b/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ClassRules.java
@@ -0,0 +1,65 @@
+package tech.picnic.errorprone.refasterrules;
+
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import java.util.function.Predicate;
+import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+
+/** Refaster rules related to expressions dealing with classes. */
+@OnlineDocumentation
+final class ClassRules {
+  private ClassRules() {}
+
+  /** Prefer {@link Class#isInstance(Object)} over more contrived alternatives. */
+  static final class ClassIsInstance<T, S> {
+    @BeforeTemplate
+    boolean before(Class<T> clazz, S object) {
+      return clazz.isAssignableFrom(object.getClass());
+    }
+
+    @AfterTemplate
+    boolean after(Class<T> clazz, S object) {
+      return clazz.isInstance(object);
+    }
+  }
+
+  /** Prefer using the {@code instanceof} keyword over less idiomatic alternatives. */
+  static final class Instanceof<T, S> {
+    @BeforeTemplate
+    boolean before(S object) {
+      return Refaster.<T>clazz().isInstance(object);
+    }
+
+    @AfterTemplate
+    boolean after(S object) {
+      return Refaster.<T>isInstance(object);
+    }
+  }
+
+  /** Prefer {@link Class#isInstance(Object)} method references over more verbose alternatives. */
+  static final class ClassLiteralIsInstancePredicate<T, S> {
+    @BeforeTemplate
+    Predicate<S> before() {
+      return o -> Refaster.<T>isInstance(o);
+    }
+
+    @AfterTemplate
+    Predicate<S> after() {
+      return Refaster.<T>clazz()::isInstance;
+    }
+  }
+
+  /** Prefer {@link Class#isInstance(Object)} method references over more verbose alternatives. */
+  static final class ClassReferenceIsInstancePredicate<T, S> {
+    @BeforeTemplate
+    Predicate<S> before(Class<T> clazz) {
+      return o -> clazz.isInstance(o);
+    }
+
+    @AfterTemplate
+    Predicate<S> after(Class<T> clazz) {
+      return clazz::isInstance;
+    }
+  }
+}
diff --git a/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ClassRulesTestInput.java b/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ClassRulesTestInput.java
new file mode 100644
index 00000000000..d59e3e18d28
--- /dev/null
+++ b/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ClassRulesTestInput.java
@@ -0,0 +1,25 @@
+package tech.picnic.errorprone.refasterrules;
+
+import com.google.common.collect.ImmutableSet;
+import java.io.IOException;
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class ClassRulesTest implements RefasterRuleCollectionTestCase {
+  boolean testClassIsInstance() throws IOException {
+    return CharSequence.class.isAssignableFrom("foo".getClass());
+  }
+
+  ImmutableSet<Boolean> testInstanceof() throws IOException {
+    Class<?> clazz = CharSequence.class;
+    return ImmutableSet.of(CharSequence.class.isInstance("foo"), clazz.isInstance("bar"));
+  }
+
+  Predicate<String> testClassLiteralIsInstancePredicate() throws IOException {
+    return s -> s instanceof CharSequence;
+  }
+
+  Predicate<String> testClassReferenceIsInstancePredicate() throws IOException {
+    Class<?> clazz = CharSequence.class;
+    return s -> clazz.isInstance(s);
+  }
+}
diff --git a/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ClassRulesTestOutput.java b/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ClassRulesTestOutput.java
new file mode 100644
index 00000000000..548fa314394
--- /dev/null
+++ b/error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/ClassRulesTestOutput.java
@@ -0,0 +1,25 @@
+package tech.picnic.errorprone.refasterrules;
+
+import com.google.common.collect.ImmutableSet;
+import java.io.IOException;
+import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
+
+final class ClassRulesTest implements RefasterRuleCollectionTestCase {
+  boolean testClassIsInstance() throws IOException {
+    return CharSequence.class.isInstance("foo");
+  }
+
+  ImmutableSet<Boolean> testInstanceof() throws IOException {
+    Class<?> clazz = CharSequence.class;
+    return ImmutableSet.of("foo" instanceof CharSequence, clazz.isInstance("bar"));
+  }
+
+  Predicate<String> testClassLiteralIsInstancePredicate() throws IOException {
+    return CharSequence.class::isInstance;
+  }
+
+  Predicate<String> testClassReferenceIsInstancePredicate() throws IOException {
+    Class<?> clazz = CharSequence.class;
+    return clazz::isInstance;
+  }
+}