Take into account api scope on minimization

build.gradle

@@ -118,4 +118,4 @@ task relocateShadowJar(type: ConfigureShadowRelocation) {
     target = tasks.shadowJar
 }
 
-tasks.shadowJar.dependsOn tasks.relocateShadowJar
+tasks.shadowJar.dependsOn tasks.relocateShadowJar

src/docs/asciidoc/15-minimizing.adoc

@@ -23,3 +23,8 @@ shadowJar {
   }
 }
 ----
+
+[NOTE]
+====
+Dependencies scoped as `api` will automatically excluded from minimization and used as "entry points" on minimization.
+====

src/main/groovy/com/github/jengelman/gradle/plugins/shadow/internal/UnusedTracker.groovy

@@ -1,6 +1,8 @@
 package com.github.jengelman.gradle.plugins.shadow.internal
 
 import org.gradle.api.Project
+import org.gradle.api.artifacts.Configuration
+import org.gradle.api.artifacts.ProjectDependency
 import org.gradle.api.file.FileCollection
 import org.gradle.api.tasks.SourceSet
 import org.vafer.jdependency.Clazz
@@ -13,9 +15,10 @@ class UnusedTracker {
     private final List<ClazzpathUnit> projectUnits
     private final Clazzpath cp = new Clazzpath()
 
-    private UnusedTracker(List<File> classDirs, FileCollection toMinimize) {
+    private UnusedTracker(List<File> classDirs, FileCollection classJars, FileCollection toMinimize) {
         this.toMinimize = toMinimize
         projectUnits = classDirs.collect { cp.addClazzpathUnit(it) }
+        projectUnits.addAll(classJars.collect { cp.addClazzpathUnit(it) })
     }
 
     Set<String> findUnused() {
@@ -33,12 +36,33 @@ class UnusedTracker {
         }
     }
 
-    static UnusedTracker forProject(Project project, FileCollection toMinimize) {
+    static UnusedTracker forProject(Project project, List<Configuration> configurations, DependencyFilter dependencyFilter) {
+        def apiJars = getApiJarsFromProject(project)
+        FileCollection toMinimize = dependencyFilter.resolve(configurations) - apiJars
+
         final List<File> classDirs = new ArrayList<>()
         for (SourceSet sourceSet in project.sourceSets) {
-            Iterable<File> classesDirs = sourceSet.output.hasProperty('classesDirs') ? sourceSet.output.classesDirs : [sourceSet.output.classesDir]
+            Iterable<File> classesDirs = sourceSet.output.classesDirs
             classDirs.addAll(classesDirs.findAll { it.isDirectory() })
         }
-        return new UnusedTracker(classDirs, toMinimize)
+        return new UnusedTracker(classDirs, apiJars, toMinimize)
+    }
+
+    private static FileCollection getApiJarsFromProject(Project project) {
+        def apiDependencies = project.configurations.asMap['api']?.dependencies ?: null
+        if (apiDependencies == null) return project.files()
+
+        def runtimeConfiguration = project.configurations.asMap['runtimeClasspath'] ?: project.configurations.runtime
+        def apiJars = new LinkedList<File>()
+        apiDependencies.each { dep ->
+            if (dep instanceof ProjectDependency) {
+                apiJars.addAll(getApiJarsFromProject(dep.dependencyProject))
+                apiJars.add(runtimeConfiguration.find { it.name.endsWith("${dep.name}.jar") } as File)
+            } else {
+                apiJars.add(runtimeConfiguration.find { it.name.startsWith("${dep.name}-") } as File)
+            }
+        }
+
+        return project.files(apiJars)
     }
 }

src/main/groovy/com/github/jengelman/gradle/plugins/shadow/tasks/ShadowJar.java

@@ -79,8 +79,7 @@ public InheritManifest getManifest() {
     @Override
     protected CopyAction createCopyAction() {
         DocumentationRegistry documentationRegistry = getServices().get(DocumentationRegistry.class);
-        FileCollection toMinimize = dependencyFilterForMinimize.resolve(configurations);
-        final UnusedTracker unusedTracker = UnusedTracker.forProject(getProject(), toMinimize);
+        final UnusedTracker unusedTracker = UnusedTracker.forProject(getProject(), configurations, dependencyFilterForMinimize);
         return new ShadowCopyAction(getArchivePath(), getInternalCompressor(), documentationRegistry,
                 this.getMetadataCharset(), transformers, relocators, getRootPatternSet(), shadowStats,
                 versionUtil, isPreserveFileTimestamps(), minimizeJar, unusedTracker);

src/test/groovy/com/github/jengelman/gradle/plugins/shadow/ShadowPluginSpec.groovy

@@ -318,6 +318,160 @@ class ShadowPluginSpec extends PluginSpecification {
         doesNotContain(serverOutput, ['client/Client.class'])
     }
 
+    /**
+     * 'api' used as api for 'impl', and depended on 'lib'. 'junit' is independent.
+     * The minimize shall remove 'junit', but not 'api'.
+     * Unused classes of 'api' and theirs dependencies also shouldn't be removed.
+     */
+    def 'use minimize with dependencies with api scope'() {
+        given:
+        file('settings.gradle') << """
+            include 'api', 'lib', 'impl'
+        """.stripIndent()
+
+        file('lib/src/main/java/lib/LibEntity.java') << """
+            package lib;
+            public interface LibEntity {}
+        """.stripIndent()
+
+        file('lib/src/main/java/lib/UnusedLibEntity.java') << """
+            package lib;
+            public class UnusedLibEntity implements LibEntity {}
+        """.stripIndent()
+
+        file('lib/build.gradle') << """
+            apply plugin: 'java'
+            repositories { maven { url "${repo.uri}" } }
+        """.stripIndent()
+
+        file('api/src/main/java/api/Entity.java') << """
+            package api;
+            public interface Entity {}
+        """.stripIndent()
+
+        file('api/src/main/java/api/UnusedEntity.java') << """
+            package api;
+            import lib.LibEntity;
+            public class UnusedEntity implements LibEntity {}
+        """.stripIndent()
+
+        file('api/build.gradle') << """
+            apply plugin: 'java'
+            repositories { maven { url "${repo.uri}" } }
+            dependencies { 
+                compile 'junit:junit:3.8.2' 
+                compile project(':lib')
+            }
+        """.stripIndent()
+
+        file('impl/src/main/java/impl/SimpleEntity.java') << """
+            package impl;
+            import api.Entity;
+            public class SimpleEntity implements Entity {}
+        """.stripIndent()
+
+        file('impl/build.gradle') << """
+            apply plugin: 'java-library'
+            apply plugin: 'com.github.johnrengelman.shadow'
+
+            shadowJar {
+                minimize()
+            }
+
+            repositories { maven { url "${repo.uri}" } }
+            dependencies { api project(':api') }
+        """.stripIndent()
+
+        File serverOutput = file('impl/build/libs/impl-all.jar')
+
+        when:
+        runner.withArguments(':impl:shadowJar', '--stacktrace').withDebug(true).build()
+
+        then:
+        contains(serverOutput, [
+                'impl/SimpleEntity.class',
+                'api/Entity.class',
+                'api/UnusedEntity.class',
+                'lib/LibEntity.class',
+        ])
+        doesNotContain(serverOutput, ['junit/framework/Test.class', 'lib/UnusedLibEntity.class'])
+    }
+
+    /**
+     * 'api' used as api for 'impl', and 'lib' used as api for 'api'.
+     * Unused classes of 'api' and 'lib' shouldn't be removed.
+     */
+    def 'use minimize with transitive dependencies with api scope'() {
+        given:
+        file('settings.gradle') << """
+            include 'api', 'lib', 'impl'
+        """.stripIndent()
+
+        file('lib/src/main/java/lib/LibEntity.java') << """
+            package lib;
+            public interface LibEntity {}
+        """.stripIndent()
+
+        file('lib/src/main/java/lib/UnusedLibEntity.java') << """
+            package lib;
+            public class UnusedLibEntity implements LibEntity {}
+        """.stripIndent()
+
+        file('lib/build.gradle') << """
+            apply plugin: 'java'
+            repositories { maven { url "${repo.uri}" } }
+        """.stripIndent()
+
+        file('api/src/main/java/api/Entity.java') << """
+            package api;
+            public interface Entity {}
+        """.stripIndent()
+
+        file('api/src/main/java/api/UnusedEntity.java') << """
+            package api;
+            import lib.LibEntity;
+            public class UnusedEntity implements LibEntity {}
+        """.stripIndent()
+
+        file('api/build.gradle') << """
+            apply plugin: 'java-library'
+            repositories { maven { url "${repo.uri}" } }
+            dependencies { api project(':lib') }
+        """.stripIndent()
+
+        file('impl/src/main/java/impl/SimpleEntity.java') << """
+            package impl;
+            import api.Entity;
+            public class SimpleEntity implements Entity {}
+        """.stripIndent()
+
+        file('impl/build.gradle') << """
+            apply plugin: 'java-library'
+            apply plugin: 'com.github.johnrengelman.shadow'
+
+            shadowJar {
+                minimize()
+            }
+
+            repositories { maven { url "${repo.uri}" } }
+            dependencies { api project(':api') }
+        """.stripIndent()
+
+        File serverOutput = file('impl/build/libs/impl-all.jar')
+
+        when:
+        runner.withArguments(':impl:shadowJar', '--stacktrace').withDebug(true).build()
+
+        then:
+        contains(serverOutput, [
+                'impl/SimpleEntity.class',
+                'api/Entity.class',
+                'api/UnusedEntity.class',
+                'lib/LibEntity.class',
+                'lib/UnusedLibEntity.class'
+        ])
+    }
+
     def 'depend on project shadow jar'() {
         given:
         file('settings.gradle') << """