chore(gradle): Improve logging of unresolved dependencies

The error message produced for an unresolved dependency was not really
helpful because the causes of the top-level
`ModuleVersionResolveException` are again exceptions of this type with
generic messages. The interesting information is found in the causes
of these exceptions.

Signed-off-by: Oliver Heger <[email protected]>

Author: oheger-bosch

plugins/package-managers/gradle-plugin/src/main/kotlin/OrtModelBuilder.kt

@@ -295,11 +295,7 @@ internal class OrtModelBuilder : ToolingModelBuilder {
                         append(dep.from)
                         append(".")
 
-                        val causes = (dep.failure as? ModuleVersionResolveException)?.causes?.takeIf { it.isNotEmpty() }
-                        if (causes != null) {
-                            appendLine(" Causes are:")
-                            append(causes.joinToString("\n") { it.toString() })
-                        }
+                        appendCauses(dep.failure)
                     }
 
                     logger.error(message)
@@ -319,3 +315,27 @@ internal class OrtModelBuilder : ToolingModelBuilder {
             }
         }
 }
+
+/**
+ * Add a string with information about the causes of the given [exception] to this [StringBuilder]. This is used to
+ * log the reason why a dependency could not be resolved. To get meaningful information, all causes need to be obtained
+ * recursively. This is because the top-level [ModuleVersionResolveException] typically has only other
+ * [ModuleVersionResolveException]s as causes with generic messages. The actual information about what went wrong is
+ * hidden somewhere down the cause chain.
+ */
+private fun StringBuilder.appendCauses(exception: Throwable) {
+    val causes = (exception as? ModuleVersionResolveException)?.causes?.takeIf { it.isNotEmpty() }
+    if (causes != null) {
+        appendLine(" Causes are:")
+        val allCauses = mutableSetOf<String>()
+
+        fun getAllCauses(exception: Throwable) {
+            exception.message?.also(allCauses::add)
+            exception.cause?.also { getAllCauses(it) }
+        }
+
+        causes.forEach { getAllCauses(it) }
+
+        append(allCauses.joinToString("\n"))
+    }
+}