Add explicit DuplicatesStrategy as required by gradle 7+ (#487)

Previous Gradle releases used a default 'include' strategy for
copy specs: if a duplicate was found, then Gradle would silently
include the duplicate, potentially overwriting the previous entry.

In Gradle 5, Gradle introduced a warning whenever duplicates are found
and that no explicit deduplication strategy is set. With Gradle 7, this 
now becomes an error.

This change fixes the issue by adding DuplicatesStrategy.INCLUDE to 
the file Copy task.

.travis.yml

@@ -22,6 +22,7 @@ env:
 
 script:
   - ./gradlew clean assemble -x signArchives test --tests com.google.protobuf.gradle.ProtobufJavaPluginTest --stacktrace
+  - ./gradlew test --tests com.google.protobuf.gradle.ProtobufKotlinDslCopySpecTest --stacktrace
   - ./gradlew test --tests com.google.protobuf.gradle.ProtobufKotlinDslPluginTest --stacktrace
   - ./gradlew test --tests com.google.protobuf.gradle.ProtobufAndroidPluginTest --stacktrace
   - ./gradlew -stop

src/main/groovy/com/google/protobuf/gradle/ProtobufExtract.groovy

@@ -33,6 +33,7 @@ import com.google.common.base.Preconditions
 import groovy.transform.CompileDynamic
 import org.gradle.api.DefaultTask
 import org.gradle.api.file.ConfigurableFileCollection
+import org.gradle.api.file.DuplicatesStrategy
 import org.gradle.api.file.FileCollection
 import org.gradle.api.file.FileSystemLocation
 import org.gradle.api.file.FileTree
@@ -113,6 +114,8 @@ abstract class ProtobufExtract extends DefaultTask {
       spec.from(allProtoFiles)
       spec.include('**/*.proto')
       spec.into(destDir)
+      // gradle 7+ requires a duplicate strategy to be explicitly defined
+      spec.duplicatesStrategy = DuplicatesStrategy.INCLUDE
     }
   }
 

src/test/groovy/com/google/protobuf/gradle/ProtobufKotlinDslCopySpecTest.groovy

@@ -0,0 +1,55 @@
+package com.google.protobuf.gradle
+
+import groovy.transform.CompileDynamic
+import org.gradle.testkit.runner.BuildResult
+import org.gradle.testkit.runner.GradleRunner
+import org.gradle.testkit.runner.TaskOutcome
+import spock.lang.Specification
+import spock.lang.Unroll
+
+/**
+ * Unit test confirming copy spec is explicitly defined for gradle7+ compliance.
+ */
+@CompileDynamic
+class ProtobufKotlinDslCopySpecTest extends Specification {
+  private static final List<String> GRADLE_VERSIONS = ["5.6", "6.0", "6.7.1", "7.0"]
+
+  @Unroll
+  void "testProjectKotlinDslCopySpec should declare explicit copy spec [gradle #gradleVersion]"() {
+    given: "project from testProjectKotlinDslCopySpec"
+    File projectDir = ProtobufPluginTestHelper.projectBuilder('testProjectKotlinDslCopySpec')
+            .copyDirs('testProjectKotlinDslCopySpec')
+            .build()
+
+    when: "build is invoked"
+    BuildResult result = GradleRunner.create()
+            .withProjectDir(projectDir)
+            .withArguments('test', 'build', '--stacktrace')
+            .withPluginClasspath()
+            .withGradleVersion(gradleVersion)
+            .forwardStdOutput(new OutputStreamWriter(System.out))
+            .forwardStdError(new OutputStreamWriter(System.err))
+            .build()
+
+    then: "it succeed"
+
+    result.task(":test").outcome == TaskOutcome.SUCCESS
+
+    verifyProjectDir(projectDir)
+
+    where:
+    gradleVersion << GRADLE_VERSIONS
+  }
+
+  private static void verifyProjectDir(File projectDir) {
+    File generatedSrcDir = new File(projectDir.path, "build/generated/source/proto/main/java")
+    List<File> fileList = []
+    generatedSrcDir.eachFileRecurse { file ->
+      if (file.path.endsWith('.java')) {
+        fileList.add (file)
+      }
+    }
+    assert fileList.size > 0
+  }
+
+}

testProjectKotlinDslCopySpec/build.gradle.kts

@@ -0,0 +1,56 @@
+import com.google.protobuf.gradle.generateProtoTasks
+import com.google.protobuf.gradle.id
+import com.google.protobuf.gradle.ofSourceSet
+import com.google.protobuf.gradle.plugins
+import com.google.protobuf.gradle.protobuf
+import com.google.protobuf.gradle.protoc
+
+buildscript {
+  repositories {
+    gradlePluginPortal()
+  }
+}
+
+plugins {
+  java
+  id("java-library")
+  id("com.google.protobuf")
+}
+
+repositories {
+  mavenCentral()
+}
+
+java {
+  sourceCompatibility = JavaVersion.VERSION_1_8
+  targetCompatibility = JavaVersion.VERSION_1_8
+}
+
+val protobufDepVersion = "3.0.0"
+val grpcVersion = "1.37.0"
+
+dependencies {
+  implementation("io.grpc:grpc-protobuf:$grpcVersion")
+  implementation("io.grpc:grpc-stub:$grpcVersion")
+  implementation("com.google.protobuf:protobuf-java:$protobufDepVersion")
+  testImplementation("org.junit.jupiter:junit-jupiter-api:5.7.1")
+  testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.7.1")
+}
+
+protobuf {
+  protoc {
+    artifact = "com.google.protobuf:protoc:$protobufDepVersion"
+  }
+  plugins {
+    id("grpc") {
+      artifact = "io.grpc:protoc-gen-grpc-java:$grpcVersion"
+    }
+  }
+}
+
+tasks {
+  test {
+    useJUnitPlatform {
+    }
+  }
+}

testProjectKotlinDslCopySpec/settings.gradle.kts

@@ -0,0 +1 @@
+rootProject.name="testProjectKotlinDslCopySpec"

testProjectKotlinDslCopySpec/src/main/proto/google/type/money.proto

@@ -0,0 +1,42 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package google.type;
+
+option cc_enable_arenas = true;
+option go_package = "google.golang.org/genproto/googleapis/type/money;money";
+option java_multiple_files = true;
+option java_outer_classname = "MoneyProto";
+option java_package = "com.google.type";
+option objc_class_prefix = "GTP";
+
+// Represents an amount of money with its currency type.
+message Money {
+  // The three-letter currency code defined in ISO 4217.
+  string currency_code = 1;
+
+  // The whole units of the amount.
+  // For example if `currencyCode` is `"USD"`, then 1 unit is one US dollar.
+  int64 units = 2;
+
+  // Number of nano (10^-9) units of the amount.
+  // The value must be between -999,999,999 and +999,999,999 inclusive.
+  // If `units` is positive, `nanos` must be positive or zero.
+  // If `units` is zero, `nanos` can be positive, zero, or negative.
+  // If `units` is negative, `nanos` must be negative or zero.
+  // For example $-1.75 is represented as `units`=-1 and `nanos`=-750,000,000.
+  int32 nanos = 3;
+}

testProjectKotlinDslCopySpec/src/test/java/com/myapp/ExampleUnitTest.java

@@ -0,0 +1,12 @@
+package com.myapp;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class ExampleUnitTest {
+
+  @Test
+  public void addition_isCorrect() {
+    Assertions.assertEquals(4, 2 + 2);
+  }
+}