# API Lint Metalava can optionally run warn about various API problems based on the Android API Council's guidelines, described in go/android-api-guidelines. These rules are not always exact. For example, you should avoid using acronyms in names; e.g. a method should be named handleUri, not handleURI. But what about getZOrder? This is probably better than getZorder, but metalava can't tell without consulting a dictionary. Therefore, there are cases where you want to say "ok, that's good advice in general, but wrong here". In order to avoid having this warningshow up again and again, there are two ways to mark an issue such that it is no longer flagged. (Note that metalava will not report issues on classes, methods and fields that are deprecated since these are presumably already known to be bad and are already discouraged.) ## Suppressing with @Suppress Next to an error message, metalava will include the issue id. For example, here's a sample error message: src/android/pkg/MyStringImpl.java:3: error: Don't expose your implementation details: MyStringImpl ends with Impl [EndsWithImpl] Here the id is "EndsWithImpl". You can suppress this with the @SuppressLint annotation: ... import android.annotation.SuppressLint; ... @SuppressLint("EndsWithImpl") public class MyStringImpl { ... ## Suppressing with baselines Metalava also has support for "baselines", which are files which record all the current warnings and errors in the codebase. When metalava runs, it looks up the baseline to see if a given issue is already listed in the baseline, and if so, it is silently ignored. You can pass a flag to metalava ("--update-baseline") to tell it to update the baseline files with any new errors it comes across instead of reporting them. With soong, if you specify the baseline explicitly, like this: --- a/Android.bp +++ b/Android.bp @@ -1678,6 +1678,7 @@ droidstubs { }, api_lint: { enabled: true, ==> baseline_filename: "api/baseline.txt", <== } jdiff_enabled: true, } then the build system will automatically supply `--update-baseline` on your behalf to a generated file in the out/ folder, and if there's a failure metalava will tell you where to find the updated baseline which you can then copy into place: ... 93 new API lint issues were found. See tools/metalava/API-LINT.md for how to handle these. ************************************************************ Your API changes are triggering API Lint warnings or errors. To make these errors go away, you have two choices: 1. You can suppress the errors with @SuppressLint("") 2. You can update the baseline by executing the following command: cp \ out/soong/.intermediates/frameworks/base/system-api-stubs-docs/android_common/api/system-baseline.txt \ frameworks/base/api/system-baseline.txt To submit the revised baseline.txt to the main Android repository, you will need approval. ************************************************************ Then re-run the build and you should now see diffs to the baseline file; git diff to make sure you're really only marking the issues you intended to include. $ git status ... Untracked files: (use "git add ..." to include in what will be committed) baseline.txt ## Copying File Manually In the near future the build system will not allow source files to be modified by the build. At that point you'll need to manually copy in the file instead. During the build, before failing, metalava will emit a message like this: ... metalava wrote updated baseline to out/something/baseline.txt ... At that point you can copy the file to where you need: ```sh $ cp out/something/baseline.txt frameworks/base/api/baseline.txt ``` ## Existing Issues You can view the exact set of existing issues (current APIs that get flagged by API lint) by inspecting the baseline files in the source tree, but to get a sense of the types of issues that are more likely to have a false positive, here's the existing distribution as of early 2019: Count Issue Id Rule Severity -------------------------------------------------- 932 ProtectedMember M7 error 321 OnNameExpected warning 288 ArrayReturn warning 269 ActionValue C4 error 266 NoByteOrShort FW12 warning 221 ExecutorRegistration L1 warning 211 AllUpper C2 error 206 GetterSetterNames M6 error 185 BannedThrow error 172 SamShouldBeLast warning 159 NoClone error 159 ParcelNotFinal FW8 error 119 NotCloseable warning 105 ListenerLast M3 warning 81 ConcreteCollection CL2 error 78 StaticUtils error 76 IntentName C3 error 74 VisiblySynchronized M5 error 72 GenericException S1 error 65 KotlinOperator warning 57 AcronymName S1 warning 55 ParcelCreator FW3 error 54 ParcelConstructor FW3 error 53 UseIcu warning 48 Enum F5 error 41 RethrowRemoteException FW9 error 37 AutoBoxing M11 error 35 StreamFiles M10 warning 28 IntentBuilderName FW1 warning 27 ServiceName C4 error 26 ListenerInterface L1 error 25 ContextFirst M3 error 25 InterfaceConstant C4 error 24 CallbackInterface CL3 error 24 RegistrationName L3 error 23 IllegalStateException S1 warning 22 EqualsAndHashCode M8 error 22 PackageLayering FW6 warning 18 MinMaxConstant C8 warning 18 SingletonConstructor error 17 MethodNameUnits error 15 MissingBuildMethod warning 15 UserHandleName warning 14 UserHandle warning 13 ResourceFieldName error 12 ManagerLookup error 11 ManagerConstructor error 9 CallbackMethodName L1 error 9 ParcelableList warning 8 CallbackName L1 warning 7 HeavyBitSet error 7 ResourceValueFieldName C7 error 6 CompileTimeConstant error 6 SetterReturnsThis M4 warning 4 EndsWithImpl error 4 TopLevelBuilder warning 4 UseParcelFileDescriptor FW11 error 3 MentionsGoogle error 3 StartWithLower S1 error 2 AbstractInner warning 2 BuilderSetStyle warning 2 OverlappingConstants C1 warning 2 PairedRegistration L2 error 2 SingularCallback L1 error 2 StartWithUpper S1 error 1 ContextNameSuffix C4 error 1 KotlinKeyword error -------------------------------------------------- 4902 (This is generated when metalava is invoked with both --verbose and --update-baseline.)