feat(MavenSupport): Improve the caching logic for empty remote artifacts

Previously, failures to look up remote artifacts were unconditionally
cached as empty artifacts. While it is hard to reliably determine the
root cause of a failed lookup, in the case that all candidate URLs do
not end with a known extension it is very likely that ORT ran into a bug
in the context of #4694. Ease debugging such cases by not anymore
caching failed lookups due to missing file extensions, and generally
improve the logging when returning an empty remote artifact.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>

analyzer/src/main/kotlin/managers/utils/MavenSupport.kt

@@ -26,7 +26,6 @@ import java.net.URI
 
 import kotlin.time.Duration.Companion.hours
 
-import org.apache.logging.log4j.Level
 import org.apache.logging.log4j.kotlin.Logging
 import org.apache.maven.artifact.repository.LegacyLocalRepositoryManager
 import org.apache.maven.bridge.MavenRepositorySystem
@@ -111,6 +110,14 @@ private val File?.safePath: String
 
 class MavenSupport(private val workspaceReader: WorkspaceReader) {
     companion object : Logging {
+        private val PACKAGING_TYPES = setOf(
+            // Core packaging types, see https://maven.apache.org/pom.html#packaging.
+            "pom", "jar", "maven-plugin", "ejb", "war", "ear", "rar",
+            // Custom packaging types, see "resources/META-INF/plexus/components.xml".
+            "aar", "apk", "bundle", "dll", "dylib", "eclipse-plugin", "gwt-app", "gwt-lib", "hk2-jar", "hpi",
+            "jenkins-module", "orbit", "so", "zip"
+        )
+
         // See http://maven.apache.org/pom.html#SCM.
         private val SCM_REGEX = Regex("scm:(?<type>[^:@]+):(?<url>.+)")
         private val USER_HOST_REGEX = Regex("scm:(?<user>[^:@]+)@(?<host>[^:]+)[:/](?<path>.+)")
@@ -635,14 +642,20 @@ class MavenSupport(private val workspaceReader: WorkspaceReader) {
             }
         }
 
-        val level = if (artifact.classifier == "sources") Level.DEBUG else Level.WARN
-        logger.log(level) {
-            "Could not find artifact $artifact in any of ${locationInfo.map { it.downloadUrl }.distinct()}."
-        }
+        return RemoteArtifact.EMPTY.also { remoteArtifact ->
+            val downloadUrls = locationInfo.map { it.downloadUrl }.distinct()
 
-        return RemoteArtifact.EMPTY.also {
-            logger.debug { "Writing empty remote artifact for '$artifact' to disk cache." }
-            remoteArtifactCache.write(cacheKey, yamlMapper.writeValueAsString(it))
+            // While for dependencies that have e.g. no sources artifact published it is completely valid to have an
+            // empty remote artifact and to cache that result, for cases where none of the tried URLs ends with an
+            // extension for a known packaging type probably some bug is the root cause for the artifact not being
+            // found, and thus such results should not be cached, but retried.
+            if (downloadUrls.any { url -> PACKAGING_TYPES.any { url.endsWith(".$it") } }) {
+                logger.debug { "Writing empty remote artifact for '$artifact' to disk cache." }
+
+                remoteArtifactCache.write(cacheKey, yamlMapper.writeValueAsString(remoteArtifact))
+            } else {
+                logger.warn { "Could not find artifact $artifact in any of $downloadUrls." }
+            }
         }
     }