[FIR] Fix calculating of completion mode

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/InferenceCompletion.kt

@@ -77,9 +77,11 @@ private fun Candidate.hasProperNonTrivialLowerConstraints(components: InferenceC
     val constructor = typeVariable.typeConstructor(context)
     val variableWithConstraints = csBuilder.currentStorage().notFixedTypeVariables[constructor] ?: return false
     val constraints = variableWithConstraints.constraints
-    return constraints.isNotEmpty() && constraints.all {
+    // TODO: support Exact annotation
+    // see KotlinCallCompleter:244
+    return constraints.isNotEmpty() && constraints.any {
         !it.type.typeConstructor(context).isIntegerLiteralTypeConstructor(context) &&
-                it.kind.isLower() && csBuilder.isProperType(it.type)
+                (it.kind.isLower() || it.kind.isEqual()) && csBuilder.isProperType(it.type)
     }
 
 }

compiler/fir/resolve/testData/resolve/stdlib/inference/complexConstraintSystem.kt

@@ -0,0 +1,5 @@
+class Inv<X>(val x: X)
+
+fun test_0(list: List<Int>, b: Boolean) {
+    val x = list.mapNotNull { if (b) Inv(it) else null }.first().x
+}

compiler/fir/resolve/testData/resolve/stdlib/inference/complexConstraintSystem.txt

@@ -0,0 +1,24 @@
+FILE: complexConstraintSystem.kt
+    public final class Inv<X> : R|kotlin/Any| {
+        public constructor<X>(x: R|X|): R|Inv<X>| {
+            super<R|kotlin/Any|>()
+        }
+
+        public final val x: R|X| = R|<local>/x|
+            public get(): R|X|
+
+    }
+    public final fun test_0(list: R|kotlin/collections/List<kotlin/Int>|, b: R|kotlin/Boolean|): R|kotlin/Unit| {
+        lval x: R|kotlin/Int| = R|<local>/list|.R|kotlin/collections/mapNotNull|<R|kotlin/Int|, R|Inv<kotlin/Int>|>(<L> = mapNotNull@fun <anonymous>(it: R|kotlin/Int|): R|Inv<kotlin/Int>?| <kind=UNKNOWN>  {
+            when () {
+                R|<local>/b| ->  {
+                    R|/Inv.Inv|<R|kotlin/Int|>(R|<local>/it|)
+                }
+                else ->  {
+                    Null(null)
+                }
+            }
+
+        }
+        ).R|kotlin/collections/first|<R|Inv<kotlin/Int>|>().R|FakeOverride</Inv.x: R|kotlin/Int|>|
+    }

compiler/fir/resolve/tests/org/jetbrains/kotlin/fir/FirDiagnosticsWithStdlibTestGenerated.java

@@ -379,6 +379,24 @@ public class FirDiagnosticsWithStdlibTestGenerated extends AbstractFirDiagnostic
         }
     }
 
+    @TestMetadata("compiler/fir/resolve/testData/resolve/stdlib/inference")
+    @TestDataPath("$PROJECT_ROOT")
+    @RunWith(JUnit3RunnerWithInners.class)
+    public static class Inference extends AbstractFirDiagnosticsWithStdlibTest {
+        private void runTest(String testDataFilePath) throws Exception {
+            KotlinTestUtils.runTest(this::doTest, this, testDataFilePath);
+        }
+
+        public void testAllFilesPresentInInference() throws Exception {
+            KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/fir/resolve/testData/resolve/stdlib/inference"), Pattern.compile("^([^.]+)\\.kt$"), true);
+        }
+
+        @TestMetadata("complexConstraintSystem.kt")
+        public void testComplexConstraintSystem() throws Exception {
+            runTest("compiler/fir/resolve/testData/resolve/stdlib/inference/complexConstraintSystem.kt");
+        }
+    }
+
     @TestMetadata("compiler/fir/resolve/testData/resolve/stdlib/j+k")
     @TestDataPath("$PROJECT_ROOT")
     @RunWith(JUnit3RunnerWithInners.class)