Search in all versions.properties, not just the first one #4830 (#4831)

* Fix multiple versions.properties files #4830

* Improve build error when multiple Detekt versions are present

Co-authored-by: Tim Oltjenbruns <tim.oltjenbruns@softvision.com>

detekt-gradle-plugin/src/main/kotlin/io/gitlab/arturbosch/detekt/extensions/DetektExtension.kt

@@ -107,17 +107,26 @@ open class DetektExtension @Inject constructor(objects: ObjectFactory) : CodeQua
     }
 }
 
-internal fun loadDetektVersion(classLoader: ClassLoader): String = Properties().run {
-    val inputStream = classLoader.getResource("versions.properties")!!.openConnection()
-        /*
-         * Due to https://bugs.openjdk.java.net/browse/JDK-6947916 and https://bugs.openjdk.java.net/browse/JDK-8155607,
-         * it is necessary to disallow caches to maintain stability on JDK 8 and 11 (and possibly more).
-         * Otherwise, simultaneous invocations of Detekt in the same VM can fail spuriously. A similar bug is referenced in
-         * https://github.com/detekt/detekt/issues/3396. The performance regression is likely unnoticeable.
-         * Due to https://github.com/detekt/detekt/issues/4332 it is included for all JDKs.
-         */
-        .apply { useCaches = false }
-        .getInputStream()
-    load(inputStream)
-    getProperty("detektVersion")
+internal fun loadDetektVersion(classLoader: ClassLoader): String {
+    // Other Gradle plugins can also have a versions.properties.
+    val distinctVersions = classLoader.getResources("versions.properties").toList().mapNotNull { versions ->
+        Properties().run {
+            val inputStream = versions.openConnection()
+                /*
+                 * Due to https://bugs.openjdk.java.net/browse/JDK-6947916 and https://bugs.openjdk.java.net/browse/JDK-8155607,
+                 * it is necessary to disallow caches to maintain stability on JDK 8 and 11 (and possibly more).
+                 * Otherwise, simultaneous invocations of Detekt in the same VM can fail spuriously. A similar bug is referenced in
+                 * https://github.com/detekt/detekt/issues/3396. The performance regression is likely unnoticeable.
+                 * Due to https://github.com/detekt/detekt/issues/4332 it is included for all JDKs.
+                 */
+                .apply { useCaches = false }
+                .getInputStream()
+            load(inputStream)
+            getProperty("detektVersion")
+        }
+    }.distinct()
+    return distinctVersions.singleOrNull() ?: error(
+        "You're importing two Detekt plugins which have different versions. " +
+            "(${distinctVersions.joinToString()}) Make sure to align the versions."
+    )
 }