gradle-animalsniffer-plugin

About

Gradle AnimalSniffer plugin for Java, Groovy (only with @CompileStatic!), Kotlin or Scala projects (may work with other jvm-based languages too). Initially, AnimalSniffer was created to check compatibility with lower Java versions (to prevent situations when newer API methods called).

But it's a general tool: signatures could be created for any library to check api compatibility against older library versions. For example, AnimalSniffer was adopted by Android community to verify lower android SDK compatibility.

Plugin implemented in the same way as core Gradle quality plugins (Checkstyle, PMD, etc.): Verification task is registered for each source set (animalsnifferMain, animalsnifferTest) and attached to the check task.

Advanced features:

• Signature build task
• Check task classpath caching to speed-up subsequent checks (useful when check runs often without clean)
• Merging check signatures (when small 3rd party lib signatures are used)
• Viewing signature content task

Used by:

• Mockito for java and android compatibility checks
• Okhttp for java and android compatibility checks (using kotlin multiplatform)

Applicability

NOTE: JDK 9+ signatires are not published:

Starting with JDK9+ you can't define a full API signature cause based on the module system you can define your own (limited view on JDK). Apart from that you can use the release configuration in maven-compiler-plugin with JDK9+ to have exactly what animal sniffer offers and that's the reason why there are no JDK9+ signatures.

To check JDK 9+ compatibility use --release flag instead of plugin (or build signatures manually with maven plugin):

compileJava {
  options.release = 11
}

Plugin could still be useful:

• For Android projects to check API compatibility (because Android API signatures are published).
• To check strong compatibility with some library: you'll need to generate signatures for this library and will be able to use them to check project compatibility (on API level, ofc) with older library versions.

Summary

• Configuration extensions:
  • animalsniffer - check configuration
  • animalsnifferSignature - signature build configuration (optional)
• Tasks:
  • check[Main] - check source set task
  • animalsnifferSignature - build signature (active when animalsnifferSignature configuration declared)
  • type:BuildSignatureTask - custom signature build task may be used to merge signatures
  • type:SignatureInfoTask - view signature "contents"
• Dependencies configuration: signature - signatures for check

Setup

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'ru.vyarus:gradle-animalsniffer-plugin:1.7.1'
    }
}
apply plugin: 'ru.vyarus.animalsniffer'

OR

plugins {
    id 'ru.vyarus.animalsniffer' version '1.7.1'
}

Example projects (with intentional errors to see output):

• Java (including android signatures)
• Groovy
• Kotlin
• Scala
• Signature build examples

Compatibility

IMPORTANT: Plugin only works when java-base plugin (activated by any java-related plugin like java-library, groovy, scala, org.jetbrains.kotlin.jvm, etc.) is enabled, otherwise nothing will be registered. There is no support for the Android plugin (java-base plugin must be used to perform animalsniffer check).

For kotlin multiplatform plugin enable java support:

kotlin {
    jvm().withJava()
}

The plugin is compiled for Java 8, and is compatible with Java 11.

Usage

Additional tasks will be assigned to the check task. So animalsniffer checks will be executed during:

$ gradlew check

NOTE: in case of configuration problems use animalsniffer.debug option to see actual task configuration

Signatures

AnimalSniffer requires a signature file to check against. To define a signature (or multiple signatures) use the signature configuration.

To check Java version compatibility:

repositories { mavenCentral() }
dependencies {
    signature 'org.codehaus.mojo.signature:java16:1.1@signature'
}

Java signatures

To check Android compatibility (in java project):

repositories { mavenCentral() }
dependencies {
    signature 'net.sf.androidscents.signature:android-api-level-14:4.0_r4@signature'
}

Android signatures

To check both Java version and Android compatibility:

dependencies {
    signature 'org.codehaus.mojo.signature:java16:1.1@signature'
    signature 'net.sf.androidscents.signature:android-api-level-14:4.0_r4@signature'
}

In the last case animalsniffer will run 2 times for each signature. You may see the same errors two times if a class/method is absent in both signatures. Each error message in the log (and file) will also contain the signature name to avoid confusion.

When no signatures are defined animalsniffer tasks will always pass.

You can also use custom libraries signatures to check version compatibility.

Scope

All project dependencies are excluded from the analysis: only classes from your source set are checked.

By default, all source sets are checked. To only check main sources:

animalsniffer {
    sourceSets = [sourceSets.main]
}

Output

Violations are always printed to the console. Example output:

2 AnimalSniffer violations were found in 1 files. See the report at: file:///myproject/build/reports/animalsniffer/main.text

[Undefined reference] invalid.(Sample.java:9)
  >> int Boolean.compare(boolean, boolean)

[Undefined reference] invalid.(Sample.java:14)
  >> java.nio.file.Path java.nio.file.Paths.get(String, String[])

NOTE: text report file will contain simplified report (error per line):

invalid.Sample:9  Undefined reference: int Boolean.compare(boolean, boolean)
invalid.Sample:14  Undefined reference: java.nio.file.Path java.nio.file.Paths.get(String, String[])

NOTE: when multiple signatures are used, output will contain the signature name in the error message to avoid confusion.

Suppress violations

An annotation could be used to suppress violations: examples

Default annotation

Add dependency on the annotation artifact:

implementation "org.codehaus.mojo:animal-sniffer-annotations:1.16"

Use provided scope if you can. Annotation is configured by default, so you can simply use annotation to suppress violation:

@IgnoreJRERequirement
private Optional param;

Custom annotation

You can define your own annotation:

package com.mycompany

@Retention(RetentionPolicy.CLASS)
@Documented
@Target({ElementType.METHOD, ElementType.CONSTRUCTOR, ElementType.TYPE})
public @interface SuppressSignatureCheck {}

Configure annotation:

animalsniffer {
    annotation = 'com.mycompany.SuppressSignatureCheck'
}

Now check will skip blocks annotated with your annotation:

@SuppressSignatureCheck
private Optional param;

Extend signature

Your project could target multiple Java versions and so reference classes, not present in a signature.

For example, your implementation could try to use Java 7 Paths and if the class is not available, fall back to the Java 6 implementation. In this case Paths could be added to the ignored classes:

animalsniffer {
    ignore 'java.nio.file.Paths'
}

Now usages of Paths will not cause warnings.

Multiple ignored classes could be defined:

animalsniffer {
    ignore 'java.nio.file.Paths', 'some.other.Class'
}

Or

animalsniffer {
    ignore 'java.nio.file.Paths'
    ignore 'some.other.Class'
}

Or by directly assigning collection:

animalsniffer {
    ignore  = ['java.nio.file.Paths', 'some.other.Class']
}

Entire packages could be ignored using asterisk:

animalsniffer {
    ignore 'some.pkg.*'
}

See more info in the documentation.

Configuration

Configuration example:

animalsniffer {
    toolVersion = '1.23'
    sourceSets = [sourceSets.main]
    ignoreFailures = true
    reportsDir = file("$project.buildDir/animalsnifferReports")
    annotation = 'com.mypackage.MyAnnotation'
    ignore = ['java.nio.file.Paths']
}

There are no required configurations - the plugin will generate defaults for all of them.

NOTE: ignore does not exclude your classes from check, it allows you to use classes not mentioned in the signature. See more details above.

Tasks

The animalsniffer task is registered for each source set:

• animalsnifferMain - run AnimalAniffer for compiled main classes
• animalsnifferTest - run AnimalSniffer for compiled test classes
• animalsniffer[SourceSet] - run AnimalSniffer for compiled [SourceSet] classes

The check task will depend only on tasks from configured in animalsniffer.sourceSets source sets.

Tasks support text report, enabled by default.

To disable reports for a task:

animalsnifferMain.reports.text.enabled = false

or for all tasks:

tasks.withType(AnimalSniffer) {
    reports.text.enabled = false
}

Animalsniffer task is a SourceTask and may be configured to include/exclude classes from check.

NOTE: The task operates on compiled classes and not sources! Be careful when defining patterns.

For example, to exclude classes in a 'invalid' subpackage from check:

animalsnifferMain {
    exclude('**/invalid/*')
}

Advanced features

Read wiki for advanced features:

• Build your project signature
• Optimize often check task calls to speed-up subsequent checks (useful when check runs often without clean)
• Merging library signatures (when small 3rd party lib signatures used)
• View signature content

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