KT-18501: Fix to find KDoc even if KDoc is in ModifierList

compiler/frontend/src/org/jetbrains/kotlin/psi/FindDocComment.kt

@@ -16,14 +16,19 @@
 
 package org.jetbrains.kotlin.psi.findDocComment
 
-import com.intellij.psi.PsiComment
-import com.intellij.psi.PsiWhiteSpace
 import org.jetbrains.kotlin.kdoc.psi.api.KDoc
 import org.jetbrains.kotlin.psi.KtDeclaration
+import org.jetbrains.kotlin.psi.KtDeclarationModifierList
 import org.jetbrains.kotlin.psi.psiUtil.allChildren
 
 fun findDocComment(declaration: KtDeclaration): KDoc? {
     return declaration.allChildren
-            .dropWhile { it !is KDoc && (it is PsiWhiteSpace || it is PsiComment) }
+            .flatMap {
-            .first() as? KDoc
+                if (it is KtDeclarationModifierList) {
+                    return@flatMap it.children.asSequence()
+                }
+                sequenceOf(it)
+            }
+            .dropWhile { it !is KDoc }
+            .firstOrNull() as? KDoc
 }

idea/testData/kdoc/finder/Annotated.kt

@@ -0,0 +1,5 @@
+class Foo() {
+    @Supress("unused")
+    /** Doc for method xyzzy */
+    fun xyzzy(): Int = 0
+}

idea/tests/org/jetbrains/kotlin/idea/kdoc/KDocFinderTest.kt

@@ -39,6 +39,15 @@ class KDocFinderTest() : LightPlatformCodeInsightFixtureTestCase() {
         Assert.assertEquals("Doc for constructor of class C.", doc!!.getContent())
     }
 
+    fun testAnnotated() {
+        myFixture.configureByFile(getTestName(false) + ".kt")
+        val declaration = (myFixture.file as KtFile).declarations[0]
+        val descriptor = declaration.resolveToDescriptor() as ClassDescriptor
+        val overriddenFunctionDescriptor = descriptor.defaultType.memberScope.getContributedFunctions(Name.identifier("xyzzy"), NoLookupLocation.FROM_TEST).single()
+        val doc = overriddenFunctionDescriptor.findKDoc()
+        Assert.assertEquals("Doc for method xyzzy", doc!!.getContent())
+    }
+
     fun testOverridden() {
         myFixture.configureByFile(getTestName(false) + ".kt")
         val declaration = (myFixture.file as KtFile).declarations.single { it.name == "Bar" }