[FE 1.0] Fix false-negative INVALID_IF_AS_EXPRESSION_WARNING and NO_ELSE_IN_WHEN_WARNING

^KT-51711 Fixed

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java

@@ -6386,6 +6386,12 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                 runTest("compiler/testData/diagnostics/tests/controlStructures/kt4310.kt");
             }
 
+            @Test
+            @TestMetadata("kt51711.kt")
+            public void testKt51711() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/controlStructures/kt51711.kt");
+            }
+
             @Test
             @TestMetadata("kt657.kt")
             public void testKt657() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java

@@ -6386,6 +6386,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/tests/controlStructures/kt4310.kt");
             }
 
+            @Test
+            @TestMetadata("kt51711.kt")
+            public void testKt51711() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/controlStructures/kt51711.kt");
+            }
+
             @Test
             @TestMetadata("kt657.kt")
             public void testKt657() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java

@@ -6386,6 +6386,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                 runTest("compiler/testData/diagnostics/tests/controlStructures/kt4310.kt");
             }
 
+            @Test
+            @TestMetadata("kt51711.kt")
+            public void testKt51711() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/controlStructures/kt51711.kt");
+            }
+
             @Test
             @TestMetadata("kt657.kt")
             public void testKt657() throws Exception {

compiler/frontend/cfg/src/org/jetbrains/kotlin/cfg/ControlFlowInformationProviderImpl.kt

@@ -955,20 +955,23 @@ class ControlFlowInformationProviderImpl private constructor(
         for (element in instruction.owner.getValueElements(value)) {
             if (element !is KtIfExpression) continue
 
-            if (element.isUsedAsExpression(trace.bindingContext)) {
-                val thenExpression = element.then
-                val elseExpression = element.`else`
+            val thenExpression = element.then
+            val elseExpression = element.`else`
+            val isEhxaustive = thenExpression != null && elseExpression != null
 
-                if (thenExpression == null || elseExpression == null) {
+            if (element.isUsedAsExpression(trace.bindingContext)) {
+                if (!isEhxaustive) {
                     trace.report(INVALID_IF_AS_EXPRESSION.on(element.ifKeyword))
                 } else {
                     checkImplicitCastOnConditionalExpression(element)
                 }
             } else if (!languageVersionSettings.supportsFeature(LanguageFeature.ProhibitNonExhaustiveIfInRhsOfElvis)) {
-                val parent = element.deparenthesizedParent
-                if (parent is KtBinaryExpression) {
-                    if (parent.operationToken === KtTokens.ELVIS) {
-                        trace.report(INVALID_IF_AS_EXPRESSION_WARNING.on(element.getIfKeyword()))
+                if (!isEhxaustive) {
+                    val parent = element.deparenthesizedParent
+                    if (parent is KtBinaryExpression) {
+                        if (parent.operationToken === KtTokens.ELVIS) {
+                            trace.report(INVALID_IF_AS_EXPRESSION_WARNING.on(element.getIfKeyword()))
+                        }
                     }
                 }
             }
@@ -1067,6 +1070,7 @@ class ControlFlowInformationProviderImpl private constructor(
                 if (
                     !usedAsExpression &&
                     missingCases.isNotEmpty() &&
+                    elseEntry == null &&
                     !languageVersionSettings.supportsFeature(LanguageFeature.ProhibitNonExhaustiveIfInRhsOfElvis)
                 ) {
                     val parent = element.deparenthesizedParent

compiler/testData/diagnostics/tests/controlStructures/kt51711.kt

@@ -0,0 +1,22 @@
+// FIR_IDENTICAL
+// LANGUAGE: -ProhibitNonExhaustiveIfInRhsOfElvis
+// ISSUE: KT-51711
+// WITH_STDLIB
+
+private fun fake(a: String?) {}
+
+fun test_1(x: String?, y: String?) {
+    while (true) {
+        x ?: if (y == null) break else fake(y)
+    }
+}
+
+
+fun test_2(x: String?, y: String?) {
+    while (true) {
+        x ?: when {
+            true -> break
+            else -> y?.filter { it.isLowerCase() }
+        }
+    }
+}

compiler/testData/diagnostics/tests/controlStructures/kt51711.txt

@@ -0,0 +1,5 @@
+package
+
+private fun fake(/*0*/ a: kotlin.String?): kotlin.Unit
+public fun test_1(/*0*/ x: kotlin.String?, /*1*/ y: kotlin.String?): kotlin.Unit
+public fun test_2(/*0*/ x: kotlin.String?, /*1*/ y: kotlin.String?): kotlin.Unit

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java

@@ -6392,6 +6392,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/controlStructures/kt4310.kt");
             }
 
+            @Test
+            @TestMetadata("kt51711.kt")
+            public void testKt51711() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/controlStructures/kt51711.kt");
+            }
+
             @Test
             @TestMetadata("kt657.kt")
             public void testKt657() throws Exception {