Implement display of code construct start for Kotlin

#KT-20470 Fixed

idea/src/META-INF/plugin.xml

@@ -774,6 +774,12 @@
 
     <gotoRelatedProvider implementation="org.jetbrains.kotlin.idea.goto.KotlinExpectOrActualGotoRelatedProvider"/>
 
+    <declarationRangeHandler key="org.jetbrains.kotlin.psi.KtClassOrObject"
+                             implementationClass="org.jetbrains.kotlin.idea.codeInsight.KotlinClassDeclarationRangeHandler"/>
+
+    <declarationRangeHandler key="org.jetbrains.kotlin.psi.KtDeclarationWithBody"
+                             implementationClass="org.jetbrains.kotlin.idea.codeInsight.KotlinFunDeclarationRangeHandler"/>
+
     <intentionAction>
       <className>org.jetbrains.kotlin.idea.intentions.FoldInitializerAndIfToElvisIntention</className>
       <category>Kotlin</category>

idea/src/org/jetbrains/kotlin/idea/KotlinPairMatcher.kt

@@ -5,11 +5,14 @@
 
 package org.jetbrains.kotlin.idea
 
+import com.intellij.codeInsight.hint.DeclarationRangeUtil
 import com.intellij.lang.BracePair
 import com.intellij.lang.PairedBraceMatcher
 import com.intellij.psi.PsiFile
 import com.intellij.psi.tree.IElementType
 import org.jetbrains.kotlin.lexer.KtTokens
+import org.jetbrains.kotlin.psi.KtBlockExpression
+import org.jetbrains.kotlin.psi.KtClassBody
 
 class KotlinPairMatcher : PairedBraceMatcher {
     private val pairs = arrayOf(
@@ -37,6 +40,12 @@ class KotlinPairMatcher : PairedBraceMatcher {
     }
 
     override fun getCodeConstructStart(file: PsiFile, openingBraceOffset: Int): Int {
-        return openingBraceOffset
+        val element = file.findElementAt(openingBraceOffset)
+        if (element == null || element is PsiFile) return openingBraceOffset
+        val parent = element.parent
+        return when (parent) {
+            is KtClassBody, is KtBlockExpression -> DeclarationRangeUtil.getDeclarationRange(parent.parent).startOffset
+            else -> openingBraceOffset
+        }
     }
 }

idea/src/org/jetbrains/kotlin/idea/codeInsight/KotlinDeclarationRangeHandler.kt

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.idea.codeInsight
+
+import com.intellij.codeInsight.hint.DeclarationRangeHandler
+import com.intellij.openapi.util.TextRange
+import com.intellij.psi.PsiNameIdentifierOwner
+import org.jetbrains.kotlin.psi.KtClassOrObject
+import org.jetbrains.kotlin.psi.KtDeclarationWithBody
+import org.jetbrains.kotlin.psi.KtNamedFunction
+import org.jetbrains.kotlin.psi.psiUtil.endOffset
+import org.jetbrains.kotlin.psi.psiUtil.getPrevSiblingIgnoringWhitespaceAndComments
+import org.jetbrains.kotlin.psi.psiUtil.startOffset
+
+class KotlinClassDeclarationRangeHandler : DeclarationRangeHandler<KtClassOrObject> {
+    override fun getDeclarationRange(container: KtClassOrObject): TextRange {
+        val body = container.getBody() ?: return container.textRange
+        val prevSibling = body.getPrevSiblingIgnoringWhitespaceAndComments()
+        return TextRange(
+            container.getDeclarationKeyword()?.startOffset ?: container.startOffset,
+            prevSibling?.endOffset ?: body.startOffset
+        )
+    }
+}
+
+class KotlinFunDeclarationRangeHandler : DeclarationRangeHandler<KtDeclarationWithBody> {
+    override fun getDeclarationRange(container: KtDeclarationWithBody): TextRange {
+        val body = container.bodyExpression ?: return container.textRange
+        val prevSibling = body.getPrevSiblingIgnoringWhitespaceAndComments()
+        return TextRange(
+            (container as? KtNamedFunction)?.funKeyword?.startOffset
+                    ?: (container as? PsiNameIdentifierOwner)?.nameIdentifier?.startOffset
+                    ?: container.modifierList?.startOffset
+                    ?: container.startOffset,
+            prevSibling?.endOffset ?: body.startOffset
+        )
+    }
+}

idea/tests/org/jetbrains/kotlin/idea/codeInsight/KotlinPairMatcherTest.kt

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.idea.codeInsight
+
+import org.jetbrains.kotlin.idea.KotlinFileType
+import org.jetbrains.kotlin.idea.KotlinPairMatcher
+import org.jetbrains.kotlin.idea.test.KotlinLightCodeInsightFixtureTestCase
+import org.jetbrains.kotlin.idea.test.KotlinLightProjectDescriptor
+import java.lang.IllegalArgumentException
+
+class KotlinPairMatcherTest : KotlinLightCodeInsightFixtureTestCase() {
+    override fun getProjectDescriptor(): KotlinLightProjectDescriptor = KotlinLightProjectDescriptor.INSTANCE
+
+    private fun doTest(testData: String) {
+        var docText = testData
+        val startPos = docText.indexOf("<start>")
+        if (startPos == -1) {
+            throw IllegalArgumentException("<start> marker not found in testdata")
+        }
+        docText = docText.replace("<start>", "")
+        val bracePos = docText.indexOf("<brace>")
+        if (bracePos == -1) {
+            throw IllegalArgumentException("<brace> marker not found in testdata")
+        }
+        docText = docText.replace("<brace>", "")
+        myFixture.configureByText(KotlinFileType.INSTANCE, docText)
+        val pos = KotlinPairMatcher().getCodeConstructStart(myFixture.file, bracePos)
+        assertEquals(startPos, pos)
+    }
+
+    fun testClass() {
+        doTest("/* Doc comment */ <start>class Foo : Bar, Baz <brace>{ fun xyzzy() { } }")
+    }
+
+    fun testFun() {
+        doTest("/* Doc comment */ <start>fun xyzzy(x: Int, y: String): Any <brace>{ }")
+    }
+}