(#) Synthetic Accessor !!! WARNING: Synthetic Accessor This is a warning. Id : `SyntheticAccessor` Summary : Synthetic Accessor Note : **This issue is disabled by default**; use `--enable SyntheticAccessor` Severity : Warning Category : Performance Platform : Android Vendor : Android Open Source Project Feedback : https://issuetracker.google.com/issues/new?component=192708 Since : 3.2.0 (September 2018) Affects : Kotlin and Java files Editing : This check runs on the fly in the IDE editor Implementation : [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/SyntheticAccessorDetector.kt) Tests : [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/SyntheticAccessorDetectorTest.kt) A private inner class which is accessed from the outer class will force the compiler to insert a synthetic accessor; this means that you are causing extra overhead. This is not important in small projects, but is important for large apps running up against the 64K method handle limit, and especially for **libraries** where you want to make sure your library is as small as possible for the cases where your library is used in an app running up against the 64K limit. !!! Tip This lint check has an associated quickfix available in the IDE. (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text src/test/pkg/AccessTest.java:33:Warning: Access to private constructor of class AccessTest requires synthetic accessor [SyntheticAccessor] new AccessTest(); // ERROR ---------------- src/test/pkg/AccessTest.java:36:Warning: Access to private field field1 of class AccessTest requires synthetic accessor [SyntheticAccessor] int f1 = field1; // ERROR ------ src/test/pkg/AccessTest.java:40:Warning: Access to private field field5 of class AccessTest requires synthetic accessor [SyntheticAccessor] Inner[] f5 = field5; // ERROR ------ src/test/pkg/AccessTest.java:42:Warning: Access to private method method1 of class AccessTest requires synthetic accessor [SyntheticAccessor] method1(); // ERROR ------- src/test/pkg/AccessTest.java:66:Warning: Access to private constructor of class AccessTest requires synthetic accessor [SyntheticAccessor] new AccessTest(); // ERROR ---------------- src/test/pkg/AccessTest.java:69:Warning: Access to private field field1 of class AccessTest requires synthetic accessor [SyntheticAccessor] int f1 = field1; // ERROR ------ src/test/pkg/AccessTest.java:73:Warning: Access to private field field5 of class AccessTest requires synthetic accessor [SyntheticAccessor] Inner[] f5 = field5; // ERROR ------ src/test/pkg/AccessTest.java:75:Warning: Access to private method method1 of class AccessTest requires synthetic accessor [SyntheticAccessor] method1(); // ERROR ------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `src/test/pkg/AccessTest.java`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers package test.pkg; @SuppressWarnings({"unused", "WeakerAccess", "FieldCanBeLocal", "ClassNameDiffersFromFileName"}) public class AccessTest { private int field1; int field2; public int field3; private final int field4 = 100; private final Inner[] field5 = new Inner[100]; private AccessTest() { } AccessTest(int x) { } private void method1() { int f = field1; // OK - private but same class } void method2() { method1(); // OK - private but same class } public void method3() { } class Inner { @SuppressWarnings("ResultOfObjectAllocationIgnored") private void innerMethod() { new AccessTest(); // ERROR new AccessTest(42); // OK - package private int f1 = field1; // ERROR int f2 = field2; // OK - package private int f3 = field3; // OK - public int f4 = field4; // OK (constants inlined) Inner[] f5 = field5; // ERROR method1(); // ERROR method2(); // OK - package private method3(); // OK - public } private void testSuppress() { //noinspection SyntheticAccessor method1(); // OK - suppressed //noinspection PrivateMemberAccessBetweenOuterAndInnerClass method1(); // OK - suppressed with IntelliJ similar inspection id //noinspection SyntheticAccessorCall method1(); // OK - suppressed with IntelliJ similar inspection id } @SuppressWarnings("PrivateMemberAccessBetweenOuterAndInnerClass") private void testSuppressAlias() { method1(); } } @SuppressWarnings("ResultOfObjectAllocationIgnored") public void viaAnonymousInner() { Object btn = new Object() { public void method4() { new AccessTest(); // ERROR new AccessTest(42); // OK - package private int f1 = field1; // ERROR int f2 = field2; // OK - package private int f3 = field3; // OK - public int f4 = field4; // OK (constants inlined) Inner[] f5 = field5; // ERROR method1(); // ERROR method2(); // OK - package private method3(); // OK - public } }; } } @SuppressWarnings("ClassNameDiffersFromFileName") class Outer { void method(AccessTest o) { // TODO: Shouldn't flag this: compiler won't accept it anyway because it's a private reference // int f = o.field1; } } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can also visit the [source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/SyntheticAccessorDetectorTest.kt) for the unit tests for this check to see additional scenarios. The above example was automatically extracted from the first unit test found for this lint check, `SyntheticAccessorDetector.testBasicJava`. To report a problem with this extracted sample, visit https://issuetracker.google.com/issues/new?component=192708. (##) Suppressing You can suppress false positives using one of the following mechanisms: * Using a suppression annotation like this on the enclosing element: ```kt // Kotlin @Suppress("SyntheticAccessor") fun method() { problematicStatement() } ``` or ```java // Java @SuppressWarnings("SyntheticAccessor") void method() { problematicStatement(); } ``` * Using a suppression comment like this on the line above: ```kt //noinspection SyntheticAccessor problematicStatement() ``` * Using a special `lint.xml` file in the source tree which turns off the check in that folder and any sub folder. A simple file might look like this: ```xml <?xml version="1.0" encoding="UTF-8"?> <lint> <issue id="SyntheticAccessor" severity="ignore" /> </lint> ``` Instead of `ignore` you can also change the severity here, for example from `error` to `warning`. You can find additional documentation on how to filter issues by path, regular expression and so on [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html). * In Gradle projects, using the DSL syntax to configure lint. For example, you can use something like ```gradle lintOptions { disable 'SyntheticAccessor' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore SyntheticAccessor ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).