Improve Muzzle version range failure diagnostics

buildSrc/src/main/kotlin/datadog/gradle/plugin/muzzle/MuzzleMavenRepoUtils.kt

@@ -155,17 +155,21 @@ internal object MuzzleMavenRepoUtils {
     var attemptCount = 0
     var range: VersionRangeResult? = null
     var failure: VersionRangeResolutionException? = null
+    val resultExceptions = mutableListOf<Pair<Int, List<Exception>>>()
     fun attemptResolve(): VersionRangeResult? {
       attemptCount++
-      return try {
-        range = system.resolveVersionRange(session, rangeRequest)
+      val result = try {
         failure = null
-        range?.takeIf { it.hasBounds() }
+        system.resolveVersionRange(session, rangeRequest)
       } catch (e: VersionRangeResolutionException) {
         failure = e
-        range = e.result ?: range
-        null
+        e.result ?: return null
       }
+      range = result
+      if (result.exceptions.isNotEmpty()) {
+        resultExceptions += attemptCount to result.exceptions.toList()
+      }
+      return result.takeIf { failure == null && it.hasBounds() }
     }
 
     repeat(4) {
@@ -195,6 +199,7 @@ internal object MuzzleMavenRepoUtils {
         rangeRequest.repositories,
         range,
         failure,
+        resultExceptions,
         attemptCount,
         waitedSeconds,
         enableBackoffRetries
@@ -275,6 +280,7 @@ internal object MuzzleMavenRepoUtils {
     repositories: List<RemoteRepository>,
     range: VersionRangeResult?,
     failure: VersionRangeResolutionException?,
+    resultExceptions: List<Pair<Int, List<Exception>>>,
     attemptCount: Int,
     waitedSeconds: Long,
     enableBackoffRetries: Boolean
@@ -303,6 +309,15 @@ internal object MuzzleMavenRepoUtils {
         appendLine("  highestVersion=${range.highestVersion ?: "<missing>"}")
         appendLine("  versionCount=${range.versions.size}")
       }
+      if (resultExceptions.isNotEmpty()) {
+        appendLine("Resolution result exceptions:")
+        resultExceptions.forEach { (attempt, exceptions) ->
+          appendLine("  Attempt $attempt:")
+          exceptions.forEach { exception ->
+            appendException(exception, "    ")
+          }
+        }
+      }
       if (failure != null) {
         appendLine("Last resolution failure:")
         appendLine("  ${failure.javaClass.name}: ${failure.message ?: "<no message>"}")
@@ -313,6 +328,20 @@ internal object MuzzleMavenRepoUtils {
     }.trimEnd()
   }
 
+  private fun StringBuilder.appendException(exception: Throwable, indent: String) {
+    var current: Throwable? = exception
+    var currentIndent = indent
+    var depth = 0
+    while (current != null && depth < 10) {
+      val prefix = if (depth == 0) "" else "Caused by: "
+      appendLine("$currentIndent$prefix${current.javaClass.name}: ${current.message ?: "<no message>"}")
+      val cause = current.cause
+      current = cause?.takeUnless { it === current }
+      currentIndent += "  "
+      depth++
+    }
+  }
+
   private fun artifactCoordinates(artifact: Artifact): String {
     val classifier = artifact.classifier?.takeUnless { it.isEmpty() }
     return listOfNotNull(

buildSrc/src/test/kotlin/datadog/gradle/plugin/muzzle/MuzzleMavenRepoUtilsTest.kt

@@ -17,6 +17,7 @@ import org.junit.jupiter.api.io.TempDir
 import org.junit.jupiter.params.ParameterizedTest
 import org.junit.jupiter.params.provider.CsvSource
 import java.io.File
+import java.io.IOException
 import java.lang.reflect.Proxy
 import java.util.concurrent.atomic.AtomicInteger
 import org.assertj.core.api.Assertions.assertThat
@@ -71,7 +72,7 @@ class MuzzleMavenRepoUtilsTest {
       versions = "[1.0,)"
     }
     val attempts = AtomicInteger()
-    val retryingSystem = repositorySystemThrowingThenResolving(
+    val retryingSystem = repositorySystemReturningAfterFailures(
       failuresBeforeSuccess = 3,
       result = createVersionRangeResult("1.0.0"),
       attempts = attempts
@@ -149,7 +150,7 @@ class MuzzleMavenRepoUtilsTest {
       versions = "[1.0,)"
     }
     val attempts = AtomicInteger()
-    val throwingSystem = repositorySystemThrowingThenResolving(
+    val throwingSystem = repositorySystemReturningAfterFailures(
       failuresBeforeSuccess = 4,
       result = createVersionRangeResult("1.0.0"),
       attempts = attempts
@@ -171,6 +172,41 @@ class MuzzleMavenRepoUtilsTest {
     assertThat(attempts).hasValue(4)
   }
 
+  @Test
+  fun `resolveVersionRange failure includes embedded result exceptions from every attempt`() {
+    val directive = MuzzleDirective().apply {
+      group = "com.example"
+      module = "mylib"
+      versions = "[1.0,)"
+    }
+    val attempts = AtomicInteger()
+    val emptyResult = createVersionRangeResult().apply {
+      addException(
+        IllegalStateException(
+          "metadata failure",
+          IOException("download failure")
+        )
+      )
+    }
+    val failingSystem = repositorySystemReturningAfterFailures(0, emptyResult, attempts)
+
+    assertThatThrownBy {
+      MuzzleMavenRepoUtils.resolveVersionRange(
+        directive,
+        failingSystem,
+        newSession(),
+        emptyList(),
+        enableBackoffRetries = false
+      )
+    }.isInstanceOf(IllegalStateException::class.java)
+      .hasMessageContaining("Resolution result exceptions:")
+      .hasMessageContaining("Attempt 1:")
+      .hasMessageContaining("Attempt 4:")
+      .hasMessageContaining("java.lang.IllegalStateException: metadata failure")
+      .hasMessageContaining("Caused by: java.io.IOException: download failure")
+    assertThat(attempts).hasValue(4)
+  }
+
   @Test
   fun `resolveVersionRange includes directive extra repositories`() {
     val repoA = publishAndGetRepo("com.example", "mylib", listOf("1.0.0", "2.0.0"), subDir = "repoA")
@@ -328,7 +364,7 @@ class MuzzleMavenRepoUtilsTest {
     return VersionRangeResult(request).apply { this.versions = versions }
   }
 
-  private fun repositorySystemThrowingThenResolving(
+  private fun repositorySystemReturningAfterFailures(
     failuresBeforeSuccess: Int,
     result: VersionRangeResult,
     attempts: AtomicInteger
@@ -349,8 +385,9 @@ class MuzzleMavenRepoUtilsTest {
           }
           result
         }
-        "toString" -> "repositorySystemThrowingThenResolving"
+        "toString" -> "repositorySystemReturningAfterFailures"
         else -> throw UnsupportedOperationException(method.name)
       }
     } as RepositorySystem
+
 }