[gradle-plugin] use empty string as default value for reporter type

diktat-gradle-plugin/src/main/kotlin/org/cqfn/diktat/plugin/gradle/DiktatExtension.kt

@@ -31,7 +31,7 @@ open class DiktatExtension(
     /**
      * Type of the reporter to use
      */
-    var reporter: String = "plain"
+    var reporter: String = ""
 
     /**
      * Destination for reporter. If empty, will write to stdout.

diktat-gradle-plugin/src/main/kotlin/org/cqfn/diktat/plugin/gradle/DiktatJavaExecTaskBase.kt

@@ -119,7 +119,7 @@ open class DiktatJavaExecTaskBase @Inject constructor(
                     addInput(it)
                 }
 
-            add(createReporterFlag(diktatExtension))
+            add(reporterFlag(diktatExtension))
         }
         project.logger.debug("Setting JavaExec args to $args")
     }
@@ -148,11 +148,14 @@ open class DiktatJavaExecTaskBase @Inject constructor(
     @Suppress("FUNCTION_BOOLEAN_PREFIX")
     override fun getIgnoreFailures(): Boolean = ignoreFailuresProp.getOrElse(false)
 
-    private fun createReporterFlag(diktatExtension: DiktatExtension): String {
-        val flag: StringBuilder = StringBuilder()
-
-        // appending the flag with the reporter
-        setReporter(diktatExtension, flag)
+    private fun reporterFlag(diktatExtension: DiktatExtension): String = buildString {
+        val reporterFlag = project.createReporterFlag(diktatExtension)
+        append(reporterFlag)
+        val isSarifReporterActive = reporterFlag.contains("sarif")
+        if (isSarifReporterActive) {
+            // need to set user.home specially for ktlint, so it will be able to put a relative path URI in SARIF
+            systemProperty("user.home", project.rootDir.toString())
+        }
 
         val outFlag = when {
             // githubActions should have higher priority than a custom input
@@ -165,40 +168,7 @@ open class DiktatJavaExecTaskBase @Inject constructor(
             else -> ""
         }
 
-        flag.append(outFlag)
-
-        return flag.toString()
-    }
-
-    private fun setReporter(diktatExtension: DiktatExtension, flag: java.lang.StringBuilder) {
-        val name = diktatExtension.reporter.trim()
-        val validReporters = listOf("sarif", "plain", "json", "html")
-        val reporterFlag = when {
-            diktatExtension.githubActions -> {
-                if (diktatExtension.reporter.isNotEmpty()) {
-                    // githubActions should have higher priority than custom input
-                    project.logger.warn("`diktat.githubActions` is set to true, so custom reporter [$name] will be ignored and SARIF reporter will be used")
-                }
-                "--reporter=sarif"
-            }
-            name.isEmpty() -> {
-                project.logger.info("Reporter name was not set. Using 'plain' reporter")
-                "--reporter=plain"
-            }
-            name !in validReporters -> {
-                project.logger.warn("Reporter name is invalid (provided value: [$name]). Falling back to 'plain' reporter")
-                "--reporter=plain"
-            }
-            else -> "--reporter=$name"
-        }
-
-        val isSarifReporterActive = reporterFlag.contains("sarif")
-        if (isSarifReporterActive) {
-            // need to set user.home specially for ktlint, so it will be able to put a relative path URI in SARIF
-            systemProperty("user.home", project.rootDir.toString())
-        }
-
-        flag.append(reporterFlag)
+        append(outFlag)
     }
 
     @Suppress("MagicNumber")

diktat-gradle-plugin/src/main/kotlin/org/cqfn/diktat/plugin/gradle/Utils.kt

@@ -7,6 +7,7 @@
 package org.cqfn.diktat.plugin.gradle
 
 import groovy.lang.Closure
+import org.gradle.api.Project
 
 @Suppress(
     "MISSING_KDOC_TOP_LEVEL",
@@ -35,3 +36,34 @@ class KotlinClosure1<in T : Any?, V : Any>(
 )
 fun <T> Any.closureOf(action: T.() -> Unit): Closure<Any?> =
     KotlinClosure1(action, this, this)
+
+/**
+ * Create CLI flag to select reporter based on [diktatExtension]
+ *
+ * @param diktatExtension project extension of type [DiktatExtension]
+ * @return CLI flag
+ */
+internal fun Project.createReporterFlag(diktatExtension: DiktatExtension): String {
+    val name = diktatExtension.reporter.trim()
+    val validReporters = listOf("sarif", "plain", "json", "html")
+    val reporterFlag = when {
+        diktatExtension.githubActions -> {
+            if (diktatExtension.reporter.isNotEmpty()) {
+                // githubActions should have higher priority than custom input
+                logger.warn("`diktat.githubActions` is set to true, so custom reporter [$name] will be ignored and SARIF reporter will be used")
+            }
+            "--reporter=sarif"
+        }
+        name.isEmpty() -> {
+            logger.info("Reporter name was not set. Using 'plain' reporter")
+            "--reporter=plain"
+        }
+        name !in validReporters -> {
+            logger.warn("Reporter name is invalid (provided value: [$name]). Falling back to 'plain' reporter")
+            "--reporter=plain"
+        }
+        else -> "--reporter=$name"
+    }
+
+    return reporterFlag
+}

diktat-gradle-plugin/src/test/kotlin/org/cqfn/diktat/plugin/gradle/DiktatGradlePluginTest.kt

@@ -38,8 +38,11 @@ class DiktatGradlePluginTest {
     }
 
     @Test
-    fun `check that the right reporter dependency added`() {
+    fun `check default reporter type value`() {
         val diktatExtension = project.extensions.getByName("diktat") as DiktatExtension
-        Assertions.assertTrue(diktatExtension.reporter == "plain")
+        Assertions.assertEquals("", diktatExtension.reporter)
+
+        val reporterFlag = project.createReporterFlag(diktatExtension)
+        Assertions.assertEquals("--reporter=plain", reporterFlag)
     }
 }