bugfix/extension-function-kdoc(#489) (#507)

### What's done:
  * Fixed bugs
  * Smoke test #1 reworked

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

@@ -34,6 +34,8 @@ import com.pinterest.ktlint.core.ast.ElementType.BLOCK
 import com.pinterest.ktlint.core.ast.ElementType.CALLABLE_REFERENCE_EXPRESSION
 import com.pinterest.ktlint.core.ast.ElementType.CALL_EXPRESSION
 import com.pinterest.ktlint.core.ast.ElementType.COLLECTION_LITERAL_EXPRESSION
+import com.pinterest.ktlint.core.ast.ElementType.COLON
+import com.pinterest.ktlint.core.ast.ElementType.DOT
 import com.pinterest.ktlint.core.ast.ElementType.FUN
 import com.pinterest.ktlint.core.ast.ElementType.KDOC
 import com.pinterest.ktlint.core.ast.ElementType.KDOC_SECTION
@@ -46,6 +48,9 @@ import com.pinterest.ktlint.core.ast.ElementType.SAFE_ACCESS_EXPRESSION
 import com.pinterest.ktlint.core.ast.ElementType.THROW
 import com.pinterest.ktlint.core.ast.ElementType.TYPE_REFERENCE
 import com.pinterest.ktlint.core.ast.ElementType.WHEN_CONDITION_WITH_EXPRESSION
+import org.cqfn.diktat.ruleset.utils.findChildAfter
+import org.cqfn.diktat.ruleset.utils.findChildBefore
+import org.cqfn.diktat.ruleset.utils.getAllChildrenWithType
 import org.jetbrains.kotlin.com.intellij.lang.ASTNode
 import org.jetbrains.kotlin.com.intellij.psi.impl.source.tree.LeafPsiElement
 import org.jetbrains.kotlin.com.intellij.psi.impl.source.tree.PsiWhiteSpaceImpl
@@ -147,7 +152,7 @@ class KdocMethods(private val configRules: List<RulesConfig>) : Rule("kdoc-metho
             return false
         }
 
-        val explicitReturnType = node.getFirstChildWithType(TYPE_REFERENCE)
+        val explicitReturnType = node.findChildAfter(COLON, TYPE_REFERENCE)
         val hasExplicitNotUnitReturnType = explicitReturnType != null && explicitReturnType.text != "Unit"
         val hasExplicitUnitReturnType = explicitReturnType != null && explicitReturnType.text == "Unit"
         val isFunWithExpressionBody = expressionBodyTypes.any { node.hasChildOfType(it) }

diktat-rules/src/test/kotlin/org/cqfn/diktat/ruleset/smoke/DiktatSmokeTest.kt

@@ -13,6 +13,7 @@ import org.cqfn.diktat.ruleset.constants.Warnings.FILE_NAME_MATCH_CLASS
 import org.cqfn.diktat.ruleset.constants.Warnings.HEADER_MISSING_IN_NON_SINGLE_CLASS_FILE
 import org.cqfn.diktat.ruleset.constants.Warnings.KDOC_NO_EMPTY_TAGS
 import org.cqfn.diktat.ruleset.constants.Warnings.MISSING_KDOC_CLASS_ELEMENTS
+import org.cqfn.diktat.ruleset.constants.Warnings.MISSING_KDOC_ON_FUNCTION
 import org.cqfn.diktat.ruleset.constants.Warnings.MISSING_KDOC_TOP_LEVEL
 import org.cqfn.diktat.ruleset.rules.DIKTAT_RULE_SET_ID
 import org.cqfn.diktat.ruleset.rules.DiktatRuleSetProvider
@@ -55,15 +56,16 @@ class DiktatSmokeTest : FixTestBase("test/smoke/src/main/kotlin",
         unfixedLintErrors.assertEquals(
                 LintError(1, 1, "$DIKTAT_RULE_SET_ID:file-naming", "${FILE_NAME_INCORRECT.warnText()} Example1Test.kt_copy", true), // todo this is a false one
                 LintError(1, 1, "$DIKTAT_RULE_SET_ID:file-naming", "${FILE_NAME_MATCH_CLASS.warnText()} Example1Test.kt_copy vs Example", true), // todo this is a false one
-                LintError(1, 1, "$DIKTAT_RULE_SET_ID:kdoc-formatting", "${KDOC_NO_EMPTY_TAGS.warnText()} @return", false),
                 LintError(3, 6, "$DIKTAT_RULE_SET_ID:kdoc-comments", "${MISSING_KDOC_TOP_LEVEL.warnText()} Example", false),
                 LintError(3, 26, "$DIKTAT_RULE_SET_ID:kdoc-comments", "${MISSING_KDOC_CLASS_ELEMENTS.warnText()} isValid", false),
                 LintError(6, 9, "$DIKTAT_RULE_SET_ID:kdoc-comments", "${MISSING_KDOC_CLASS_ELEMENTS.warnText()} foo", false),
-                LintError(8, 19, "$DIKTAT_RULE_SET_ID:kdoc-formatting", "${KDOC_NO_EMPTY_TAGS.warnText()} @return", false),
-                LintError(10, 5, "$DIKTAT_RULE_SET_ID:empty-block-structure", EMPTY_BLOCK_STRUCTURE_ERROR.warnText() +
+                LintError(8, 8, "$DIKTAT_RULE_SET_ID:kdoc-comments", "${MISSING_KDOC_CLASS_ELEMENTS.warnText()} foo", false),
+                LintError(8, 8, "$DIKTAT_RULE_SET_ID:kdoc-methods", "${MISSING_KDOC_ON_FUNCTION.warnText()} foo", false),
+                LintError(9, 3, "$DIKTAT_RULE_SET_ID:empty-block-structure", EMPTY_BLOCK_STRUCTURE_ERROR.warnText() +
                         " empty blocks are forbidden unless it is function with override keyword", false),
-                LintError(12, 41, "$DIKTAT_RULE_SET_ID:kdoc-formatting", "${KDOC_NO_EMPTY_TAGS.warnText()} @return", false),
-                LintError(14, 34, "$DIKTAT_RULE_SET_ID:kdoc-formatting", "${KDOC_NO_EMPTY_TAGS.warnText()} @return", false)
+                LintError(12, 10, "$DIKTAT_RULE_SET_ID:kdoc-formatting", "${KDOC_NO_EMPTY_TAGS.warnText()} @return", false),
+                LintError(14, 3, "$DIKTAT_RULE_SET_ID:kdoc-formatting", "${KDOC_NO_EMPTY_TAGS.warnText()} @return", false),
+                LintError(19, 15, "$DIKTAT_RULE_SET_ID:kdoc-formatting", "${KDOC_NO_EMPTY_TAGS.warnText()} @return", false)
         )
     }
 

diktat-rules/src/test/resources/test/paragraph2/kdoc/package/src/main/kotlin/org/cqfn/diktat/kdoc/methods/ReturnTagInsertionExpected.kt

@@ -28,4 +28,16 @@ class Example {
      * @throws IllegalStateException never
      */
     fun test4(a: Int): Int = 0
+
+    /**
+     * Lorem ipsum
+     * @throws IllegalStateException never
+     */
+    fun test5() = 0
+
+    /**
+     * Lorem ipsum
+     * @throws IllegalStateException never
+     */
+    fun A.test6() = 0
 }

diktat-rules/src/test/resources/test/paragraph2/kdoc/package/src/main/kotlin/org/cqfn/diktat/kdoc/methods/ReturnTagInsertionTested.kt

@@ -24,4 +24,16 @@ class Example {
      * @throws IllegalStateException never
      */
     fun test4(a: Int): Int = 0
+
+    /**
+     * Lorem ipsum
+     * @throws IllegalStateException never
+     */
+    fun test5() = 0
+
+    /**
+     * Lorem ipsum
+     * @throws IllegalStateException never
+     */
+    fun A.test6() = 0
 }

diktat-rules/src/test/resources/test/smoke/src/main/kotlin/Example1Expected.kt

@@ -5,9 +5,6 @@ class Example {
     val isValid = true
     val foo: Int = 1
 
-    /**
-     * @return
-     */
     fun Foo.foo() { }
 
     /**