feat: give more actionable advice regarding binary incompatibilities due to duplication on the classpath.

build.gradle.kts

@@ -2,8 +2,6 @@
 // SPDX-License-Identifier: Apache-2.0
 @file:Suppress("UnstableApiUsage", "HasPlatformType", "PropertyName")
 
-import org.jetbrains.kotlin.cli.common.toBooleanLenient
-
 plugins {
   id("java-gradle-plugin")
   id("com.gradle.plugin-publish")
@@ -182,7 +180,7 @@ fun maxParallelForks() =
 
 val isCi = providers.environmentVariable("CI")
   .getOrElse("false")
-  .toBooleanLenient()!!
+  .toBoolean()
 
 // This will slow down tests on CI, but maybe it won't run out of metaspace.
 fun forkEvery(): Long = if (isCi) 40 else 0

src/functionalTest/groovy/com/autonomousapps/AbstractFunctionalSpec.groovy

@@ -11,13 +11,16 @@ import spock.lang.Specification
 
 abstract class AbstractFunctionalSpec extends Specification {
 
+  @SuppressWarnings('unused')
+  protected static final String FLAG_LOG_BYTECODE = "-D${Flags.FLAG_BYTECODE_LOGGING}=true"
+
   protected static final GRADLE_7_5 = GradleVersion.version('7.5.1')
   protected static final GRADLE_7_6 = GradleVersion.version('7.6.2')
   protected static final GRADLE_8_0 = GradleVersion.version('8.0.2')
   protected static final GRADLE_8_4 = GradleVersion.version('8.4')
   protected static final GRADLE_8_9 = GradleVersion.version('8.9')
   protected static final GRADLE_8_10 = GradleVersion.version('8.10.2')
-  protected static final GRADLE_8_11 = GradleVersion.version('8.11-rc-1')
+  protected static final GRADLE_8_11 = GradleVersion.version('8.11')
 
   protected static final GRADLE_LATEST = GRADLE_8_10
 
@@ -26,11 +29,26 @@ abstract class AbstractFunctionalSpec extends Specification {
   protected static final SUPPORTED_GRADLE_VERSIONS = [
     GradleVersions.minGradleVersion,
     GRADLE_LATEST,
-//    GRADLE_8_11,
+    //GRADLE_8_11,
   ]
 
   protected GradleProject gradleProject = null
 
+  /**
+   * <a href="https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/store-information-in-variables#default-environment-variables">Default environment variables on Github Actions</a>
+   */
+  private static boolean isCi = System.getenv("CI") == "true"
+
+  def cleanup() {
+    // Delete fixtures on CI to prevent disk space growing out of bounds
+    if (gradleProject != null && isCi) {
+      try {
+        gradleProject.rootDir.deleteDir()
+      } catch (Throwable t) {
+      }
+    }
+  }
+
   protected static Boolean quick() {
     return System.getProperty('com.autonomousapps.quick').toBoolean()
   }

src/functionalTest/groovy/com/autonomousapps/jvm/DuplicateClasspathSpec.groovy

@@ -1,7 +1,8 @@
 package com.autonomousapps.jvm
 
+import com.autonomousapps.jvm.projects.BinaryIncompatibilityProject
 import com.autonomousapps.jvm.projects.DuplicateClasspathProject
-import org.gradle.testkit.runner.TaskOutcome
+import com.autonomousapps.utils.Colors
 
 import static com.autonomousapps.advice.truth.BuildHealthSubject.buildHealth
 import static com.autonomousapps.utils.Runner.build
@@ -17,13 +18,19 @@ final class DuplicateClasspathSpec extends AbstractJvmSpec {
     gradleProject = project.gradleProject
 
     when:
-    // This first invocation "fixes" the dependency declarations
+    // This first invocation fixes the dependency declarations
     build(gradleVersion, gradleProject.rootDir, ':consumer:fixDependencies')
-    // This second invocation fails because the fix (+ sort) causes the JVM to load the wrong class during compilation.
-    def result = buildAndFail(gradleVersion, gradleProject.rootDir, 'buildHealth')
+    // This used to fail because of classpath duplication and the wrong dep getting loaded first. Recent improvements
+    // have improved this case, however.
+    build(gradleVersion, gradleProject.rootDir, 'buildHealth')
 
     then:
-    assertThat(result.task(':consumer:compileJava').outcome).isEqualTo(TaskOutcome.FAILED)
+    assertThat(gradleProject.rootDir.toPath().resolve('consumer/build.gradle').text).contains(
+      '''\
+        dependencies {
+          implementation project(':producer-2')
+        }'''.stripIndent()
+    )
 
     where:
     gradleVersion << [GRADLE_LATEST]
@@ -35,7 +42,7 @@ final class DuplicateClasspathSpec extends AbstractJvmSpec {
     gradleProject = project.gradleProject
 
     when:
-    def result = build(gradleVersion, gradleProject.rootDir, 'buildHealth')
+    def result = buildAndFail(gradleVersion, gradleProject.rootDir, 'buildHealth')
 
     then:
     assertThat(result.output).contains(
@@ -45,11 +52,11 @@ final class DuplicateClasspathSpec extends AbstractJvmSpec {
 
         Source set: main
         \\--- compile classpath
-             +--- com/example/producer/Producer$Inner.class is provided by multiple dependencies: [:producer-1, :producer-2]
-             \\--- com/example/producer/Producer.class is provided by multiple dependencies: [:producer-1, :producer-2]
+             +--- com/example/producer/Producer is provided by multiple dependencies: [:producer-1, :producer-2]
+             \\--- com/example/producer/Producer$Inner is provided by multiple dependencies: [:producer-1, :producer-2]
         \\--- runtime classpath
-             +--- com/example/producer/Producer$Inner.class is provided by multiple dependencies: [:producer-1, :producer-2]
-             \\--- com/example/producer/Producer.class is provided by multiple dependencies: [:producer-1, :producer-2]'''
+             +--- com/example/producer/Producer is provided by multiple dependencies: [:producer-1, :producer-2]
+             \\--- com/example/producer/Producer$Inner is provided by multiple dependencies: [:producer-1, :producer-2]'''
         .stripIndent()
     )
 
@@ -61,4 +68,108 @@ final class DuplicateClasspathSpec extends AbstractJvmSpec {
     where:
     gradleVersion << [GRADLE_LATEST]
   }
+
+  def "can report on which of the duplicates is needed for binary compatibility (#gradleVersion)"() {
+    given:
+    def project = new BinaryIncompatibilityProject()
+    gradleProject = project.gradleProject
+
+    when:
+    def result = build(
+      gradleVersion, gradleProject.rootDir,
+      ':consumer:reason', '--id', ':producer-1',
+      //FLAG_LOG_BYTECODE,
+    )
+
+    then:
+    assertThat(Colors.decolorize(result.output)).contains(
+      '''\
+        ------------------------------------------------------------
+        You asked about the dependency ':producer-1'.
+        There is no advice regarding this dependency.
+        ------------------------------------------------------------
+
+        Shortest path from :consumer to :producer-1 for compileClasspath:
+        :consumer
+        \\--- :unused
+              \\--- :producer-1
+
+        Shortest path from :consumer to :producer-1 for runtimeClasspath:
+        :consumer
+        \\--- :unused
+              \\--- :producer-1
+
+        Shortest path from :consumer to :producer-1 for testCompileClasspath:
+        :consumer
+        \\--- :unused
+              \\--- :producer-1
+
+        Shortest path from :consumer to :producer-1 for testRuntimeClasspath:
+        :consumer
+        \\--- :unused
+              \\--- :producer-1
+
+        Source: main
+        ------------
+        * Is binary-incompatible, and should be removed from the classpath:
+          Expected METHOD com/example/producer/Person.<init>(Ljava/lang/String;Ljava/lang/String;)V, but was com/example/producer/Person.<init>(Ljava/lang/String;)V
+
+        Source: test
+        ------------
+        (no usages)'''.stripIndent()
+    )
+
+    where:
+    gradleVersion << [GRADLE_LATEST]
+  }
+
+  def "suggests removing a binary-incompatible duplicate (#gradleVersion)"() {
+    given:
+    def project = new BinaryIncompatibilityProject(true)
+    gradleProject = project.gradleProject
+
+    when:
+    def result = build(
+      gradleVersion, gradleProject.rootDir,
+      ':consumer:reason', '--id', ':producer-1',
+      //FLAG_LOG_BYTECODE,
+    )
+
+    then:
+    assertThat(Colors.decolorize(result.output)).contains(
+      '''\
+        ------------------------------------------------------------
+        You asked about the dependency ':producer-1'.
+        You have been advised to remove this dependency from 'implementation'.
+        ------------------------------------------------------------
+
+        Shortest path from :consumer to :producer-1 for compileClasspath:
+        :consumer
+        \\--- :producer-1
+
+        Shortest path from :consumer to :producer-1 for runtimeClasspath:
+        :consumer
+        \\--- :producer-1
+
+        Shortest path from :consumer to :producer-1 for testCompileClasspath:
+        :consumer
+        \\--- :producer-1
+
+        Shortest path from :consumer to :producer-1 for testRuntimeClasspath:
+        :consumer
+        \\--- :producer-1
+
+        Source: main
+        ------------
+        * Is binary-incompatible, and should be removed from the classpath:
+          Expected METHOD com/example/producer/Person.<init>(Ljava/lang/String;Ljava/lang/String;)V, but was com/example/producer/Person.<init>(Ljava/lang/String;)V
+
+        Source: test
+        ------------
+        (no usages)'''.stripIndent()
+    )
+
+    where:
+    gradleVersion << [GRADLE_LATEST]
+  }
 }