Fix the race condition introduced with 3470888

### What's done:

 - Original issue: #1548.
 - Original PR: #1553.
 - This change reverts 3470888.
 - Enhances the KDoc of `DiktatRule`.
 - Fixes #1548.

diktat-common/src/main/kotlin/org/cqfn/diktat/common/config/rules/RulesConfigReader.kt

@@ -18,7 +18,6 @@ import java.io.File
 import java.util.Locale
 import java.util.concurrent.atomic.AtomicInteger
 
-import kotlinx.serialization.ExperimentalSerializationApi
 import kotlinx.serialization.Serializable
 import kotlinx.serialization.decodeFromString
 
@@ -84,7 +83,6 @@ open class RulesConfigReader(override val classLoader: ClassLoader) : JsonResour
      * @param fileStream a [BufferedReader] representing loaded rules config file
      * @return list of [RulesConfig]
      */
-    @OptIn(ExperimentalSerializationApi::class)
     override fun parseResource(fileStream: BufferedReader): List<RulesConfig> = fileStream.use { stream ->
         yamlSerializer.decodeFromString<List<RulesConfig>>(stream.readLines().joinToString(separator = "\n")).reversed().distinctBy { it.name }
     }
@@ -99,19 +97,16 @@ open class RulesConfigReader(override val classLoader: ClassLoader) : JsonResour
     override fun getConfigFile(resourceFileName: String): BufferedReader? {
         val resourceFile = File(resourceFileName)
         return if (resourceFile.exists()) {
-            log.debug("Using diktat-analysis.yml file from the following path: ${resourceFile.absolutePath}")
+            log.debug("Using $DIKTAT_ANALYSIS_CONF file from the following path: ${resourceFile.absolutePath}")
             File(resourceFileName).bufferedReader()
         } else {
-            log.debug("Using the default diktat-analysis.yml file from the class path")
+            log.debug("Using the default $DIKTAT_ANALYSIS_CONF file from the class path")
             classLoader.getResourceAsStream(resourceFileName)?.bufferedReader()
         }
     }
 
     companion object {
-        /**
-         * A [Logger] that can be used
-         */
-        val log: KLogger = KotlinLogging.loggerWithKtlintConfig(RulesConfigReader::class)
+        internal val log: KLogger = KotlinLogging.loggerWithKtlintConfig(RulesConfigReader::class)
     }
 }
 

diktat-rules/src/main/kotlin/org/cqfn/diktat/ruleset/rules/DiktatRule.kt

@@ -14,7 +14,7 @@ import org.jetbrains.kotlin.com.intellij.lang.ASTNode
 private typealias DiktatConfigRule = org.cqfn.diktat.common.config.rules.Rule
 
 /**
- * This is a wrapper around Ktlint Rule
+ * This is a wrapper around _KtLint_ `Rule`.
  *
  * @param id id of the rule
  * @property configRules all rules from configuration
@@ -33,7 +33,17 @@ abstract class DiktatRule(
     var isFixMode: Boolean = false
 
     /**
-     * Will be initialized in visit
+     * The **file-specific** error emitter, initialized in
+     * [beforeVisitChildNodes] and used in [logic] implementations.
+     *
+     * Since the file is indirectly a part of the state of a `Rule`, the same
+     * `Rule` instance should **never be re-used** to check more than a single
+     * file, or confusing effects (incl. race conditions) will occur.
+     * See the documentation of the [Rule] class for more details.
+     *
+     * @see Rule
+     * @see beforeVisitChildNodes
+     * @see logic
      */
     lateinit var emitWarn: EmitType
 

diktat-rules/src/main/kotlin/org/cqfn/diktat/ruleset/rules/DiktatRuleSetProvider.kt

@@ -108,16 +108,7 @@ class DiktatRuleSetProvider(private var diktatConfigFile: String = DIKTAT_ANALYS
         yield(resolveConfigFileFromJarLocation())
         yield(resolveConfigFileFromSystemProperty())
     }
-
-    /**
-     * As of _KtLint_ **0.47**, each rule is expected to have a state and is executed
-     * twice per file, and a new `Rule` instance is created per each file checked.
-     *
-     * Diktat rules have no mutable state yet and use the deprecated _KtLint_
-     * API, so we initialize them only _once_ for performance reasons and also
-     * to avoid redundant logging.
-     */
-    private val ruleSet: RuleSet by lazy {
+    private val configRules: List<RulesConfig> by lazy {
         log.debug("Will run $DIKTAT_RULE_SET_ID with $diktatConfigFile" +
                 " (it can be placed to the run directory or the default file from resources will be used)")
         val configPath = possibleConfigs
@@ -137,10 +128,20 @@ class DiktatRuleSetProvider(private var diktatConfigFile: String = DIKTAT_ANALYS
                 diktatConfigFile
             }
 
-        val configRules = RulesConfigReader(javaClass.classLoader)
+        RulesConfigReader(javaClass.classLoader)
             .readResource(diktatConfigFile)
             ?.onEach(::validate)
             ?: emptyList()
+    }
+
+    @Suppress(
+        "LongMethod",
+        "TOO_LONG_FUNCTION",
+    )
+    @Deprecated(
+        "Marked for removal in KtLint 0.48. See changelog or KDoc for more information.",
+    )
+    override fun get(): RuleSet {
         // Note: the order of rules is important in autocorrect mode. For example, all rules that add new code should be invoked before rules that fix formatting.
         // We don't have a way to enforce a specific order, so we should just be careful when adding new rules to this list and, when possible,
         // cover new rules in smoke test as well. If a rule needs to be at a specific position in a list, please add comment explaining it (like for NewlinesRule).
@@ -229,18 +230,12 @@ class DiktatRuleSetProvider(private var diktatConfigFile: String = DIKTAT_ANALYS
             .map {
                 it.invoke(configRules)
             }
-        RuleSet(
+        return RuleSet(
             DIKTAT_RULE_SET_ID,
             rules = rules.toTypedArray()
         ).ordered()
     }
 
-    @Deprecated(
-        "Marked for removal in KtLint 0.48. See changelog or KDoc for more information.",
-    )
-    override fun get(): RuleSet =
-        ruleSet
-
     private fun validate(config: RulesConfig) =
         require(config.name == DIKTAT_COMMON || config.name in Warnings.names) {
             val closestMatch = Warnings.names.minByOrNull { Levenshtein.distance(it, config.name) }