Call chain into sequence: add 'flatten' to conversion targets #KT-26969 Fixed

idea/src/org/jetbrains/kotlin/idea/inspections/collections/ConvertCallChainIntoSequenceInspection.kt

@@ -219,6 +219,7 @@ private val transformations = listOf(
     "filterIsInstance",
     "filterNot",
     "filterNotNull",
+    "flatten",
     "map",
     "mapIndexed",
     "mapIndexedNotNull",

idea/testData/inspectionsLocal/collections/convertCallChainIntoSequence/flatten.kt

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+fun test() {
+    listOf(listOf(1), listOf(2)).<caret>flatten().filter { it > 1 }
+}

idea/testData/inspectionsLocal/collections/convertCallChainIntoSequence/flatten.kt.after

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+fun test() {
+    listOf(listOf(1), listOf(2)).asSequence().flatten().filter { it > 1 }.toList()
+}

idea/testData/inspectionsLocal/collections/convertCallChainIntoSequence/flatten2.kt

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+fun test() {
+    listOf(listOf(1), listOf(2, 3)).<caret>filter { it.size > 1 }.flatten()
+}

idea/testData/inspectionsLocal/collections/convertCallChainIntoSequence/flatten2.kt.after

@@ -0,0 +1,4 @@
+// WITH_RUNTIME
+fun test() {
+    listOf(listOf(1), listOf(2, 3)).asSequence().filter { it.size > 1 }.flatten().toList()
+}

idea/tests/org/jetbrains/kotlin/idea/inspections/LocalInspectionTestGenerated.java

@@ -569,6 +569,16 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
                 runTest("idea/testData/inspectionsLocal/collections/convertCallChainIntoSequence/endsWithGroupingBy.kt");
             }
 
+            @TestMetadata("flatten.kt")
+            public void testFlatten() throws Exception {
+                runTest("idea/testData/inspectionsLocal/collections/convertCallChainIntoSequence/flatten.kt");
+            }
+
+            @TestMetadata("flatten2.kt")
+            public void testFlatten2() throws Exception {
+                runTest("idea/testData/inspectionsLocal/collections/convertCallChainIntoSequence/flatten2.kt");
+            }
+
             @TestMetadata("implicitReceiver.kt")
             public void testImplicitReceiver() throws Exception {
                 runTest("idea/testData/inspectionsLocal/collections/convertCallChainIntoSequence/implicitReceiver.kt");