K2: Postpone inference forks resolution until FULL completion

It helps to use expected type information when choosing the branch
even in the nested calls

^KT-43296 In Progress

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

@@ -14282,6 +14282,12 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                 runTest("compiler/testData/diagnostics/tests/inference/smartCastForkForExpectType.kt");
             }
 
+            @Test
+            @TestMetadata("smartCastForkForExpectedTypeNested.kt")
+            public void testSmartCastForkForExpectedTypeNested() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/smartCastForkForExpectedTypeNested.kt");
+            }
+
             @Test
             @TestMetadata("specialCallsWithCallableReferences.kt")
             public void testSpecialCallsWithCallableReferences() throws Exception {

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

@@ -14282,6 +14282,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/tests/inference/smartCastForkForExpectType.kt");
             }
 
+            @Test
+            @TestMetadata("smartCastForkForExpectedTypeNested.kt")
+            public void testSmartCastForkForExpectedTypeNested() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/smartCastForkForExpectedTypeNested.kt");
+            }
+
             @Test
             @TestMetadata("specialCallsWithCallableReferences.kt")
             public void testSpecialCallsWithCallableReferences() throws Exception {

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

@@ -14282,6 +14282,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                 runTest("compiler/testData/diagnostics/tests/inference/smartCastForkForExpectType.kt");
             }
 
+            @Test
+            @TestMetadata("smartCastForkForExpectedTypeNested.kt")
+            public void testSmartCastForkForExpectedTypeNested() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/smartCastForkForExpectedTypeNested.kt");
+            }
+
             @Test
             @TestMetadata("specialCallsWithCallableReferences.kt")
             public void testSpecialCallsWithCallableReferences() throws Exception {

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

@@ -62,7 +62,9 @@ class ConstraintSystemCompleter(components: BodyResolveComponents, private val c
     ) {
         val topLevelTypeVariables = topLevelType.extractTypeVariables()
 
-        resolveForkPointsConstraints()
+        if (completionMode == ConstraintSystemCompletionMode.FULL) {
+            resolveForkPointsConstraints()
+        }
 
         completion@ while (true) {
             // TODO: This is very slow

compiler/resolution.common/src/org/jetbrains/kotlin/resolve/calls/inference/model/NewConstraintSystemImpl.kt

@@ -276,6 +276,7 @@ class NewConstraintSystemImpl(
         storage.errors.addAll(otherSystem.errors)
         storage.fixedTypeVariables.putAll(otherSystem.fixedTypeVariables)
         storage.postponedTypeVariables.addAll(otherSystem.postponedTypeVariables)
+        storage.constraintsFromAllForkPoints.addAll(otherSystem.constraintsFromAllForkPoints)
     }
 
     // ResultTypeResolver.Context, ConstraintSystemBuilder

compiler/testData/diagnostics/tests/inference/smartCastForkForExpectedTypeNested.fir.kt

@@ -0,0 +1,30 @@
+// SKIP_TXT
+
+interface Slice<V>
+
+interface A
+interface B : A
+interface C : A
+
+val SL0: Slice<A> = TODO()
+val SL1: Slice<B> = TODO()
+val SL2: Slice<C> = TODO()
+
+fun <X> foo(s: Slice<X>): X? {
+    if (s.hashCode() == 0) {
+        return id(bar(s))
+    }
+
+    if (s === SL0) {
+        return id(bar(s))
+    }
+
+    if (s === SL1 || s === SL2) {
+        return id(bar(s))
+    }
+    return null
+}
+
+fun <T> id(x: T): T = x
+
+fun <Y> bar(w: Slice<Y>): Y? = null

compiler/testData/diagnostics/tests/inference/smartCastForkForExpectedTypeNested.kt

@@ -0,0 +1,30 @@
+// SKIP_TXT
+
+interface Slice<V>
+
+interface A
+interface B : A
+interface C : A
+
+val SL0: Slice<A> = TODO()
+val SL1: Slice<B> = TODO()
+val SL2: Slice<C> = TODO()
+
+fun <X> foo(s: Slice<X>): X? {
+    if (s.hashCode() == 0) {
+        return id(bar(s))
+    }
+
+    if (s === SL0) {
+        return <!TYPE_MISMATCH, TYPE_MISMATCH!>id(bar(<!DEBUG_INFO_SMARTCAST!>s<!>))<!>
+    }
+
+    if (s === SL1 || s === SL2) {
+        return id(bar(s))
+    }
+    return null
+}
+
+fun <T> id(x: T): T = x
+
+fun <Y> bar(w: Slice<Y>): Y? = null

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

@@ -14288,6 +14288,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/inference/smartCastForkForExpectType.kt");
             }
 
+            @Test
+            @TestMetadata("smartCastForkForExpectedTypeNested.kt")
+            public void testSmartCastForkForExpectedTypeNested() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/smartCastForkForExpectedTypeNested.kt");
+            }
+
             @Test
             @TestMetadata("specialCallsWithCallableReferences.kt")
             public void testSpecialCallsWithCallableReferences() throws Exception {