Handle implicit receivers more accurately in if-then to safe access

#KT-26599 Fixed

idea/src/org/jetbrains/kotlin/idea/intentions/branchedTransformations/IfThenUtils.kt

@@ -215,14 +215,14 @@ data class IfThenToSelectData(
                         baseClause is KtDotQualifiedExpression -> baseClause.replaceFirstReceiver(
                             factory, newReceiver!!, safeAccess = true
                         )
-                        hasImplicitReceiver() -> factory.createExpressionByPattern("$0?.$1", newReceiver!!, baseClause).insertSafeCalls(
+                        hasImplicitReceiverReplaceableBySafeCall() -> factory.createExpressionByPattern("$0?.$1", newReceiver!!, baseClause).insertSafeCalls(
                             factory
                         )
                         baseClause is KtCallExpression -> replacedBaseClauseWithLet(baseClause, newReceiver!!, factory)
                         else -> error("Illegal state")
                     }
                 }
-                hasImplicitReceiver() -> factory.createExpressionByPattern("this?.$0", baseClause).insertSafeCalls(factory)
+                hasImplicitReceiverReplaceableBySafeCall() -> factory.createExpressionByPattern("this?.$0", baseClause).insertSafeCalls(factory)
                 baseClause is KtCallExpression -> replacedBaseClauseWithLet(baseClause, receiverExpression, factory)
                 else -> baseClause.insertSafeCalls(factory)
             }
@@ -235,7 +235,8 @@ data class IfThenToSelectData(
         return resolvedCall.getImplicitReceiverValue()
     }
 
-    internal fun hasImplicitReceiver(): Boolean = getImplicitReceiver() != null
+    internal fun hasImplicitReceiverReplaceableBySafeCall(): Boolean =
+        receiverExpression is KtThisExpression && getImplicitReceiver() != null
 
     private fun replacedBaseClauseWithLet(baseClause: KtCallExpression, receiver: KtExpression, factory: KtPsiFactory): KtExpression {
         val needExplicitParameter = baseClause.valueArguments.any { it.getArgumentExpression()?.text == "it" }
@@ -295,15 +296,15 @@ internal fun KtIfExpression.buildSelectTransformationData(): IfThenToSelectData?
     return IfThenToSelectData(context, condition, receiverExpression, baseClause, negatedClause)
 }
 
-internal fun KtExpression?.isClauseTransformableToLetOnly() =
+internal fun KtExpression?.isClauseTransformableToLetOnly(receiver: KtExpression?) =
-    this is KtCallExpression && resolveToCall()?.getImplicitReceiverValue() == null
+    this is KtCallExpression && (resolveToCall()?.getImplicitReceiverValue() == null || receiver !is KtThisExpression)
 
 internal fun KtIfExpression.shouldBeTransformed(): Boolean {
     val condition = condition
     return when (condition) {
         is KtBinaryExpression -> {
             val baseClause = (if (condition.operationToken == KtTokens.EQEQ) `else` else then)?.unwrapBlockOrParenthesis()
-            !baseClause.isClauseTransformableToLetOnly()
+            !baseClause.isClauseTransformableToLetOnly(checkedExpression())
         }
         else -> false
     }

idea/src/org/jetbrains/kotlin/idea/intentions/branchedTransformations/intentions/IfThenToElvisIntention.kt

@@ -54,7 +54,7 @@ class IfThenToElvisIntention : SelfTargetingOffsetIndependentIntention<KtIfExpre
                 false
             baseClause.evaluatesTo(receiverExpression) ->
                 true
-            receiverExpression is KtThisExpression && hasImplicitReceiver() || baseClause.hasFirstReceiverOf(receiverExpression) ->
+            hasImplicitReceiverReplaceableBySafeCall() || baseClause.hasFirstReceiverOf(receiverExpression) ->
                 !baseClause.hasNullableType(context)
             else ->
                 false

idea/testData/inspectionsLocal/branched/ifThenToSafeAccess/replaceWithLetInMember.kt

@@ -0,0 +1,14 @@
+// HIGHLIGHT: INFORMATION
+// WITH_RUNTIME
+
+class Test {
+    fun doAThing(param1: String) {
+
+    }
+
+    fun doAThingIfPresent(param1: String?) {
+        <caret>if (param1 != null) {
+            doAThing(param1)
+        }
+    }
+}

idea/testData/inspectionsLocal/branched/ifThenToSafeAccess/replaceWithLetInMember.kt.after

@@ -0,0 +1,12 @@
+// HIGHLIGHT: INFORMATION
+// WITH_RUNTIME
+
+class Test {
+    fun doAThing(param1: String) {
+
+    }
+
+    fun doAThingIfPresent(param1: String?) {
+        param1?.let { doAThing(it) }
+    }
+}

idea/testData/inspectionsLocal/branched/ifThenToSafeAccess/replaceWithLetInMemberWithIs.kt

@@ -0,0 +1,14 @@
+// HIGHLIGHT: INFORMATION
+// WITH_RUNTIME
+
+class Test {
+    fun doAThing(param1: String) {
+
+    }
+
+    fun doAThingIfPresent(param1: String?) {
+        <caret>if (param1 is String) {
+            doAThing(param1)
+        }
+    }
+}

idea/testData/inspectionsLocal/branched/ifThenToSafeAccess/replaceWithLetInMemberWithIs.kt.after

@@ -0,0 +1,12 @@
+// HIGHLIGHT: INFORMATION
+// WITH_RUNTIME
+
+class Test {
+    fun doAThing(param1: String) {
+
+    }
+
+    fun doAThingIfPresent(param1: String?) {
+        (param1 as? String)?.let { doAThing(it) }
+    }
+}

idea/testData/intentions/branched/ifThenToElvis/replaceWithLetInMember.kt

@@ -0,0 +1,17 @@
+// IS_APPLICABLE: false
+// WITH_RUNTIME
+
+class Test {
+    fun doAThing(param1: String): String {
+        return param1
+    }
+
+    fun doAThingIfPresent(param1: String?) {
+        // In theory could propose transformation to 'let'
+        <caret>if (param1 != null) {
+            doAThing(param1)
+        } else {
+            ""
+        }
+    }
+}

idea/testData/intentions/branched/ifThenToElvis/replaceWithLetInMemberWithIs.kt

@@ -0,0 +1,17 @@
+// IS_APPLICABLE: false
+// WITH_RUNTIME
+
+class Test {
+    fun doAThing(param1: String): String {
+        return param1
+    }
+
+    fun doAThingIfPresent(param1: String?) {
+        // In theory could propose transformation to 'let'
+        <caret>if (param1 is String) {
+            doAThing(param1)
+        } else {
+            ""
+        }
+    }
+}

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

@@ -286,6 +286,16 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
                 runTest("idea/testData/inspectionsLocal/branched/ifThenToSafeAccess/propertyWithProperty.kt");
             }
 
+            @TestMetadata("replaceWithLetInMember.kt")
+            public void testReplaceWithLetInMember() throws Exception {
+                runTest("idea/testData/inspectionsLocal/branched/ifThenToSafeAccess/replaceWithLetInMember.kt");
+            }
+
+            @TestMetadata("replaceWithLetInMemberWithIs.kt")
+            public void testReplaceWithLetInMemberWithIs() throws Exception {
+                runTest("idea/testData/inspectionsLocal/branched/ifThenToSafeAccess/replaceWithLetInMemberWithIs.kt");
+            }
+
             @TestMetadata("rhsEqualsNull.kt")
             public void testRhsEqualsNull() throws Exception {
                 runTest("idea/testData/inspectionsLocal/branched/ifThenToSafeAccess/rhsEqualsNull.kt");

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTestGenerated.java

@@ -2426,6 +2426,16 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
                 runTest("idea/testData/intentions/branched/ifThenToElvis/otherBlockHasMoreThanOneStatement.kt");
             }
 
+            @TestMetadata("replaceWithLetInMember.kt")
+            public void testReplaceWithLetInMember() throws Exception {
+                runTest("idea/testData/intentions/branched/ifThenToElvis/replaceWithLetInMember.kt");
+            }
+
+            @TestMetadata("replaceWithLetInMemberWithIs.kt")
+            public void testReplaceWithLetInMemberWithIs() throws Exception {
+                runTest("idea/testData/intentions/branched/ifThenToElvis/replaceWithLetInMemberWithIs.kt");
+            }
+
             @TestMetadata("rhsEqualsNull.kt")
             public void testRhsEqualsNull() throws Exception {
                 runTest("idea/testData/intentions/branched/ifThenToElvis/rhsEqualsNull.kt");