FIR: Fix inference when unit value should be cast to Any

compiler/fir/analysis-tests/legacy-fir-tests/tests-gen/org/jetbrains/kotlin/fir/LazyBodyIsNotTouchedTilContractsPhaseTestGenerated.java

@@ -2485,6 +2485,11 @@ public class LazyBodyIsNotTouchedTilContractsPhaseTestGenerated extends Abstract
         public void testTypeDepthForTypeAlias() throws Exception {
             runTest("compiler/fir/analysis-tests/testData/resolve/inference/typeDepthForTypeAlias.kt");
         }
+
+        @TestMetadata("unitUpperBound.kt")
+        public void testUnitUpperBound() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/resolve/inference/unitUpperBound.kt");
+        }
     }
 
     @TestMetadata("compiler/fir/analysis-tests/testData/resolve/inlineClasses")

compiler/fir/analysis-tests/testData/resolve/inference/unitUpperBound.fir.txt

@@ -0,0 +1,15 @@
+FILE: unitUpperBound.kt
+    public final class A : R|kotlin/Any| {
+        public constructor(): R|A| {
+            super<R|kotlin/Any|>()
+        }
+
+        public final fun foo(x: R|kotlin/collections/List<kotlin/String>|): R|kotlin/Unit| {
+            lvar w: R|kotlin/Int| = Int(1)
+            R|<local>/x|.R|kotlin/collections/ifEmpty|<R|kotlin/collections/List<kotlin/String>|, R|kotlin/Any|>(<L> = ifEmpty@fun <anonymous>(): R|kotlin/Any| <inline=Inline, kind=UNKNOWN>  {
+                R|<local>/w| = R|<local>/w|.R|kotlin/Int.plus|(Int(2))
+            }
+            )
+        }
+
+    }

compiler/fir/analysis-tests/testData/resolve/inference/unitUpperBound.kt

@@ -0,0 +1,11 @@
+// WITH_STDLIB
+// FULL_JDK
+
+class A {
+    fun foo(x: List<String>) {
+        var w = 1
+        x.ifEmpty {
+            w += 2
+        }
+    }
+}

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

@@ -2828,6 +2828,12 @@ public class FirDiagnosticTestGenerated extends AbstractFirDiagnosticTest {
             public void testTypeDepthForTypeAlias() throws Exception {
                 runTest("compiler/fir/analysis-tests/testData/resolve/inference/typeDepthForTypeAlias.kt");
             }
+
+            @Test
+            @TestMetadata("unitUpperBound.kt")
+            public void testUnitUpperBound() throws Exception {
+                runTest("compiler/fir/analysis-tests/testData/resolve/inference/unitUpperBound.kt");
+            }
         }
 
         @Nested

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

@@ -2828,6 +2828,12 @@ public class FirDiagnosticsWithLightTreeTestGenerated extends AbstractFirDiagnos
             public void testTypeDepthForTypeAlias() throws Exception {
                 runTest("compiler/fir/analysis-tests/testData/resolve/inference/typeDepthForTypeAlias.kt");
             }
+
+            @Test
+            @TestMetadata("unitUpperBound.kt")
+            public void testUnitUpperBound() throws Exception {
+                runTest("compiler/fir/analysis-tests/testData/resolve/inference/unitUpperBound.kt");
+            }
         }
 
         @Nested

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/inference/PostponedArgumentsAnalyzer.kt

@@ -197,10 +197,9 @@ class PostponedArgumentsAnalyzer(
         }
 
         if (!hasExpressionInReturnArguments && lambdaReturnType != null) {
-            /*LambdaArgumentConstraintPosition(lambda)*/
-            c.getBuilder().addEqualityConstraint(
-                lambdaReturnType,
+            c.getBuilder().addSubtypeConstraint(
                 components.session.builtinTypes.unitType.type,
+                lambdaReturnType,
                 ConeLambdaArgumentConstraintPosition(lambda.atom)
             )
         }