Restore quick doc for it parameter and this of extension function

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

@@ -24,6 +24,7 @@ import com.intellij.lang.java.JavaDocumentationProvider
 import com.intellij.openapi.diagnostic.Logger
 import com.intellij.psi.PsiElement
 import com.intellij.psi.PsiManager
+import com.intellij.psi.PsiWhiteSpace
 import org.jetbrains.kotlin.asJava.LightClassUtil
 import org.jetbrains.kotlin.asJava.elements.KtLightDeclaration
 import org.jetbrains.kotlin.config.LanguageVersionSettings
@@ -151,6 +152,23 @@ class KotlinQuickDocumentationProvider : AbstractDocumentationProvider() {
         }
 
         private fun getText(element: PsiElement, originalElement: PsiElement?, quickNavigation: Boolean): String? {
+            if (element is PsiWhiteSpace) {
+                val itElement = findElementWithText(originalElement, "it")
+                val itReference = itElement?.getParentOfType<KtNameReferenceExpression>(false)
+                if (itReference != null) {
+                    return getText(itReference, originalElement, quickNavigation)
+                }
+            }
+
+            if (element is KtTypeReference) {
+                val declaration = element.parent
+                if (declaration is KtCallableDeclaration && declaration.receiverTypeReference == element) {
+                    val thisElement = findElementWithText(originalElement, "this")
+                    if (thisElement != null) {
+                        return getText(declaration, originalElement, quickNavigation)
+                    }
+                }
+            }
 
             if (element is KtClass && element.isEnum()) {
                 // When caret on special enum function (e.g SomeEnum.values<caret>())
@@ -301,5 +319,14 @@ class KotlinQuickDocumentationProvider : AbstractDocumentationProvider() {
 
             return null
         }
+
+        private fun findElementWithText(element: PsiElement?, text: String): PsiElement? {
+            return when {
+                element == null -> null
+                element.text == text -> element
+                element.prevLeaf()?.text == text -> element.prevLeaf()
+                else -> null
+            }
+        }
     }
 }

idea/testData/editor/quickDoc/AtImplicitLambdaParametEnd.kt

@@ -0,0 +1,7 @@
+fun foo() {
+    listOf(1).forEach {
+        println(it<caret>)
+    }
+}
+
+//INFO: <pre><b>value-parameter</b> it: Int</pre>

idea/testData/editor/quickDoc/AtImplicitLambdaParameter.kt

@@ -1,6 +1,6 @@
 fun foo() {
     listOf(1).forEach {
-        println(it<caret>)
+        println(i<caret>t)
     }
 }
 

idea/testData/editor/quickDoc/ExtensionReceiver.kt

@@ -0,0 +1,10 @@
+
+interface Foo
+
+fun foo(a: Any) {}
+
+fun Foo.bar() {
+    foo(th<caret>is)
+}
+
+//INFO: <pre><b>public</b> <b>fun</b> <a href="psi_element://Foo">Foo</a>.bar(): Unit <i>defined in</i> root package</pre>

idea/testData/editor/quickDoc/ExtensionReceiverEnd.kt

@@ -0,0 +1,10 @@
+
+interface Foo
+
+fun foo(a: Any) {}
+
+fun Foo.bar() {
+    foo(this<caret>)
+}
+
+//INFO: <pre><b>public</b> <b>fun</b> <a href="psi_element://Foo">Foo</a>.bar(): Unit <i>defined in</i> root package</pre>

idea/tests/org/jetbrains/kotlin/idea/editor/quickDoc/QuickDocProviderTestGenerated.java

@@ -48,6 +48,12 @@ public class QuickDocProviderTestGenerated extends AbstractQuickDocProviderTest
         doTest(fileName);
     }
 
+    @TestMetadata("AtImplicitLambdaParametEnd.kt")
+    public void testAtImplicitLambdaParametEnd() throws Exception {
+        String fileName = KotlinTestUtils.navigationMetadata("idea/testData/editor/quickDoc/AtImplicitLambdaParametEnd.kt");
+        doTest(fileName);
+    }
+
     @TestMetadata("AtImplicitLambdaParameter.kt")
     public void testAtImplicitLambdaParameter() throws Exception {
         String fileName = KotlinTestUtils.navigationMetadata("idea/testData/editor/quickDoc/AtImplicitLambdaParameter.kt");
@@ -90,6 +96,18 @@ public class QuickDocProviderTestGenerated extends AbstractQuickDocProviderTest
         doTest(fileName);
     }
 
+    @TestMetadata("ExtensionReceiver.kt")
+    public void testExtensionReceiver() throws Exception {
+        String fileName = KotlinTestUtils.navigationMetadata("idea/testData/editor/quickDoc/ExtensionReceiver.kt");
+        doTest(fileName);
+    }
+
+    @TestMetadata("ExtensionReceiverEnd.kt")
+    public void testExtensionReceiverEnd() throws Exception {
+        String fileName = KotlinTestUtils.navigationMetadata("idea/testData/editor/quickDoc/ExtensionReceiverEnd.kt");
+        doTest(fileName);
+    }
+
     @TestMetadata("IndentedCodeBlock.kt")
     public void testIndentedCodeBlock() throws Exception {
         String fileName = KotlinTestUtils.navigationMetadata("idea/testData/editor/quickDoc/IndentedCodeBlock.kt");