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JApicmp Gradle Plugin

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The japicmp-gradle-plugin provides binary compatibility reporting through JApicmp using Gradle.

Installation

This plugin requires Gradle 6+. Use the following snippet inside a Gradle build file:

plugins {
    id 'me.champeau.gradle.japicmp' version '0.4.1'
}

or (not recommended):

build.gradle
buildscript {
    repositories {
        mavenCentral()
    }

    dependencies {
        classpath 'me.champeau.gradle:japicmp-gradle-plugin:0.4.1'
    }
}
apply plugin: 'me.champeau.gradle.japicmp'

Configuration

The plugin provides a new task type: me.champeau.gradle.japicmp.JapicmpTask that you can use to compare two jars. This task exposes the following properties as part of its configuration:

oldClasspath

The classpath of the baseline library to compare. Type: FileCollection

newClasspath

The classpath of the current version of the library, which you want to check binary compatibility Type: FileCollection

oldArchives

The jar files which will be used as the baseline for comparison. Type: FileCollection.

newArchives

The jar files we want to analyze. Type: Type: FileCollection.

onlyModified

Outputs only modified classes/methods. If not set to true, all classes and methods are printed. Type: boolean. Default value: false

onlyBinaryIncompatibleModified

Outputs only classes/methods with modifications that result in binary incompatibility. Type: boolean. Default value: false

reportOnlySummary

Reports only a breakdown of classes and their status. Type: boolean. Default value: false

packageIncludes

List of package names to include, * can be used as wildcard. Type: List<String>

packageExcludes

List of package names to exclude, * can be used as wildcard. Type: List<String>

classIncludes

List of classes to include. Type: List<String>

classExcludes

List of classes to exclude. Type: List<String>

methodIncludes

List of methods to include. Type: List<String>

methodExcludes

List of methods to exclude. Type: List<String>

fieldIncludes

List of fields to include. Type: List<String>

fieldExcludes

List of fields to exclude. Type: List<String>

annotationIncludes

List of annotations to include. The string must begin with '@'. Type: List<String>

annotationExcludes

List of annotations to exclude. The string must begin with '@'. Type: List<String>

compatibilityChangeExcludes

List of compatibility changes to exclude, marking them as source and binary compatible. The string must match a value of the japicmp.model.JApiCompatibilityChange enum. Type: List<String>

accessModifier

Sets the access modifier level (public, package, protected, private). Type: String. Default value: public

failOnSourceIncompatibility

Fails if the changes result in source level incompatibility. Setting this to true also implicitly enables failOnModification. imType: boolean. Default value: false

failOnModification

When set to true, the build fails in case a modification has been detected. Type: boolean. Default value: false

xmlOutputFile

Path to the generated XML report. Type: File. Default value: null

htmlOutputFile

Path to the generated HTML report. Type: File. Default value: null

mdOutputFile

Path to the generated Markdown report. Type: File. Default value: null

txtOutputFile

Path to the generated TXT report. Type: File. Default value: null

semverOutputFile

Path to the generated semantic versioning report. Type: File. Default value: null

includeSynthetic

Synthetic classes and class members (like e.g. bridge methods) are not tracked per default. This new option enables the tracking of such kind of classes and class members

ignoreMissingClasses

Ignores all superclasses or interfaces that missing on the classpath. Default value: false

If you don’t set oldArchives and newArchives, the plugin will infer them from the oldClasspath and newClasspath properties:

  • if you set the classpath to a configuration, the archives to compare will be the first level dependencies of that configuration

  • if you set the classpath to a simple file collection, all archives will be compared

Usage

Add the following to your build file:

tasks.register("japicmp", me.champeau.gradle.japicmp.JapicmpTask) {
    oldClasspath.from(files('path/to/reference.jar'))
    newClasspath.from(tasks.named('jar'))
    onlyModified = true
    failOnModification = true
    txtOutputFile = layout.buildDirectory.file("reports/japi.txt")
}

JApiCompatibilityChange filtering

The plugin supports simple exclusion for identified compatibility changes, turning these into binary and source compatible during API comparison:

tasks.register("japicmp", me.champeau.gradle.japicmp.JapicmpTask) {
   ...
   compatibilityChangeExcludes = [ "METHOD_NEW_DEFAULT" ]
}

The JApiCompatibilityChange enum from japicmp represents the list of identified compatibility changes which can be excluded. For simplicity, the plugin is configured with a List<String> instead.

Custom filtering

The plugin supports adding filters for bytecode members before they are considered for API comparison:

tasks.register("japicmp", me.champeau.gradle.japicmp.JapicmpTask) {
   ...
   addIncludeFilter(MyCustomFilter)
   addExcludeFilter(MyOtherFilter)
}

where MyIncludeFilter and MyExcludeFilter are classes implementing types inheriting from japicmp.filter.Filter.

For example, adding the following filter as an exclude filter will hide fields that are annotated with @Custom or have a name that contains Custom from the API comparison:

class MyOtherFilter implements FieldFilter {
    @Override
    boolean matches(CtField field) {
        return field.hasAnnotation("Custom") || field.name.contains("Custom")
    }
}

Custom reports and failure conditions

The plugin supports a DSL to generate custom reports based on the API comparison result. This has several advantages:

  • you can generate a report that focuses only on your public API, leaving the internal APIs out

  • you can implement custom rules to determine if the build should fail or not

  • the report can be presented to users and provide guidance for migration from one version to the other

Configuration

The report can be configured using the richReport block:

tasks.register("japicmp", me.champeau.gradle.japicmp.JapicmpTask) {
   ...
   richReport {
      ...
   }
}

Options for the rich report are:

renderer

The renderer used to generate the report. By default, it uses the GroovyReportRenderer

includedClasses

A list of strings representing inclusion patterns (interpreted as regular expressions). Only classes matching this pattern will be included.

excludedClasses

A list of strings representing exclusion patterns. If a class fully qualified name matches any of those patterns, it will not be included.

destinationDir

the directory where to store the report

reportName

file name of the generated report (defaults to rich-report.html)

title

a title for the report

description

a description for the report

addDefaultRules

a boolean, indicating whether the default rules should be added or not.

If no rules are explicitly defined, the default rules are applied. If any rule is added, the default rules won’t be applied unless addDefaultRules is set to true.

Custom rules

Rules are used to add violations to the report. The "violation" term must be taken in a simple sense, as it represents data to be shown in the report, whether it’s a critical violation or just information.

A violation consists of a triplet (member, severity, explanation), that will be seen in the report. For example, if a binary incompatibility is found, you can create a violation using:

Violation.notBinaryCompatible(member)

which will automatically assign it to the error severity, leading in a build failure. However, it is possible to create any kind of violation, and even accept binary incompatible changes.

Rules can be applied to 3 different levels:

  • all members (a generic rule applied unconditionnaly)

  • on specific change types (NEW, REMOVED, UNCHANGED, MODIFIED), see JApiChangeStatus

  • on specific compatibility change descriptors (see JApiCompatibilityChange)

Rules are executed in the following order:

  1. status change first

  2. specific compatibility change

  3. generic rules

For example, imagine that we want to check that all new methods are annotated with @Incubating (this is a rule in the Gradle project). Then, you need to create a rule class which will implement that check:

class IncubatingMissingRule implements ViolationRule {
    @Override
    Violation maybeViolation(final JApiCompatibility member) {
        if (member instanceof JApiMethod) {
            if (!member.annotations.find { it.fullyQualifiedName == 'org.gradle.api.Incubating' }) {
                if (!member.jApiClass.annotations.find {
                    it.fullyQualifiedName == 'org.gradle.api.Incubating'
                }) {
                    Violation.error(member, "New method is not annotated with @Incubating")
                }
            }
        }
    }
}

and then you need to configure the report to use that rule:

richReport {
   addRule(JApiChangeStatus.NEW, IncubatingMissingRule)
}

Rules can take arguments, but those are limited to Map<String, String>. For example, the following rule will mark a binary breaking change as an error, unless it is reviewed and accepted. The list of acceptations is passed as an argument to the rule:

class AcceptedRegressionRule implements ViolationRule {
    private final Map<String, String> acceptedViolations

    public AcceptedRegressionRule(Map<String, String> params) {
        acceptedViolations = params
    }

    @Override
    Violation maybeViolation(final JApiCompatibility member) {
        if (!member.binaryCompatible) {
            def acceptation = acceptedViolations[Violation.describe(member)]
            if (acceptation) {
                Violation.accept(member, acceptation)
            } else {
                Violation.notBinaryCompatible(member)
            }
        }
    }
}

and here’s how the rule is applied:

richReport {
   addRule(AcceptedRegressionRule, acceptedViolations)
}

Setup and post-process rules

Since release 0.2.2, the plugin also supports setup and post-process rules. Setup rules allow setting up some global context that can be accessed by rules extending AbstractContextAwareViolationRule. This can be useful when you need to share data between rules, and perform a final check in a post-process rule.

Setup rules need to implement SetupRule:

class MySetupRule implements SetupRule {

    @Override
    void execute(final ViolationCheckContext violationCheckContext) {
        // this is going to be executed before any other rule is executed
        violationCheckContext.userData.executed = false
    }
}

and declared using addSetupRule:

richReport {
   addSetupRule(MySetupRule)
}

Then the context can be accessed in rules implementing AbstractContextAwareViolationRule:

class ContextAwareRule extends AbstractContextAwareViolationRule {

    @Override
    Violation maybeViolation(final JApiCompatibility member) {
        // this rule is accessing the global context and can mutate user data
        context.userData.executed = true

        return null
    }
}

And then a post-process rule has access to the user data, and can also mutate the actual list of violations per class, before the report is generated:

class MyTearDownRule implements PostProcessViolationsRule {

    @Override
    void execute(final ViolationCheckContextWithViolations violationCheckContextWithViolations) {
        // this rule is executed once all checks have been performed, just before the generation
        // of the report
        // it gives the opportunity to add additional violations, or filter them, or fail
        // with a custom error
        assert violationCheckContextWithViolations.userData.executed == true
        assert !violationCheckContextWithViolations.violations.isEmpty()
    }
}

It needs to be wired in using the addPostProcessRule hook:

richReport {
   addPostProcessRule(MySetupRule)
}

Avoiding multiple violations for the same class

Since 0.2.5, it is now possible to track which members have already resulted in a violation. Since rules are executed in order, and that you can have a rule applied for a status change and a generic rule applied on the same member, it was possible for a member to trigger multiple violations. To avoid this, you can make your rule extend AbstractRecordingSeenMembers. This rule requires the RecordSeenMembersSetup to be applied, and it will only add a violation, if no other violation for the same member was added before.