K2: Refine handling of Delegate resolution mode

- Move it out of the ContextDependent hierarchy
- Get rid of many controversial checks that were necessary because
Delegate was a ContextDependent inheritor
- Actually fix semantics for lambda processing

Previously, lambdas as delegate expression were not being analyzed
thus leading to an exception (see KT-64635), and this change
forces analyzing them in the same mode as ContextIndependent
(thus `{}` made by default `() -> Unit` leaving to DELEGATE_SPECIAL_FUNCTION_MISSING)

Before this change, new test was failing with an exception.

I've analyzed all `is ContextDependent` and it seems that none of them
is relevant to delegates.

^KT-64635 Fixed

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java

@@ -10687,6 +10687,12 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
                     runTest("compiler/testData/diagnostics/tests/delegatedProperty/inference/labeledDelegatedExpression.kt");
                 }
 
+                @Test
+                @TestMetadata("lambdaDelegate.kt")
+                public void testLambdaDelegate() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/delegatedProperty/inference/lambdaDelegate.kt");
+                }
+
                 @Test
                 @TestMetadata("lambdaWithMultipleReturns.kt")
                 public void testLambdaWithMultipleReturns() throws Exception {

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java

@@ -10687,6 +10687,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
                     runTest("compiler/testData/diagnostics/tests/delegatedProperty/inference/labeledDelegatedExpression.kt");
                 }
 
+                @Test
+                @TestMetadata("lambdaDelegate.kt")
+                public void testLambdaDelegate() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/delegatedProperty/inference/lambdaDelegate.kt");
+                }
+
                 @Test
                 @TestMetadata("lambdaWithMultipleReturns.kt")
                 public void testLambdaWithMultipleReturns() throws Exception {

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

@@ -10681,6 +10681,12 @@ public class FirLightTreeOldFrontendDiagnosticsTestGenerated extends AbstractFir
                     runTest("compiler/testData/diagnostics/tests/delegatedProperty/inference/labeledDelegatedExpression.kt");
                 }
 
+                @Test
+                @TestMetadata("lambdaDelegate.kt")
+                public void testLambdaDelegate() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/delegatedProperty/inference/lambdaDelegate.kt");
+                }
+
                 @Test
                 @TestMetadata("lambdaWithMultipleReturns.kt")
                 public void testLambdaWithMultipleReturns() throws Exception {

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

@@ -10687,6 +10687,12 @@ public class FirPsiOldFrontendDiagnosticsTestGenerated extends AbstractFirPsiDia
                     runTest("compiler/testData/diagnostics/tests/delegatedProperty/inference/labeledDelegatedExpression.kt");
                 }
 
+                @Test
+                @TestMetadata("lambdaDelegate.kt")
+                public void testLambdaDelegate() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/delegatedProperty/inference/lambdaDelegate.kt");
+                }
+
                 @Test
                 @TestMetadata("lambdaWithMultipleReturns.kt")
                 public void testLambdaWithMultipleReturns() throws Exception {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/ResolutionMode.kt

@@ -23,10 +23,11 @@ sealed class ResolutionMode(
             override fun toString(): String = "ContextDependent"
         }
 
-        data object Delegate : ContextDependent()
         data object AugmentedAssignmentCallOption : ContextDependent(skipCompletion = true)
     }
 
+    data object Delegate : ResolutionMode(forceFullCompletion = false)
+
     data object ContextIndependent : ResolutionMode(forceFullCompletion = true)
 
     sealed class ReceiverResolution(val forCallableReference: Boolean) : ResolutionMode(forceFullCompletion = true) {

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

@@ -63,7 +63,7 @@ class FirPCLAInferenceSession(
 
         // Integrating back would happen at FirDelegatedPropertyInferenceSession.completeSessionOrPostponeIfNonRoot
         // after all other delegation-related calls are being analyzed
-        if (resolutionMode == ResolutionMode.ContextDependent.Delegate) return
+        if (resolutionMode == ResolutionMode.Delegate) return
 
         currentCommonSystem.replaceContentWith(candidate.system.currentStorage())
 
@@ -211,7 +211,7 @@ class FirPCLAInferenceSession(
         }
         if (callInfo.arguments.any { it.isQualifiedAccessContainingTypeVariables() || it.doesArgumentUseOuterCS() }) return true
 
-        if (callInfo.resolutionMode is ResolutionMode.ContextDependent.Delegate) return true
+        if (callInfo.resolutionMode is ResolutionMode.Delegate) return true
 
         // For assignments like myVarContainingTV = SomeCallWithNonTrivialInference(...)
         // We should integrate the call into the PCLA tree, too

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirDeclarationsResolveTransformer.kt

@@ -440,7 +440,7 @@ open class FirDeclarationsResolveTransformer(
     }
 
     private fun transformDelegateExpression(delegate: FirWrappedDelegateExpression): FirExpression =
-        delegate.expression.transformSingle(transformer, ResolutionMode.ContextDependent.Delegate)
+        delegate.expression.transformSingle(transformer, ResolutionMode.Delegate)
             .transformSingle(components.integerLiteralAndOperatorApproximationTransformer, null)
 
     /**
@@ -1024,7 +1024,12 @@ open class FirDeclarationsResolveTransformer(
             }
             is ResolutionMode.WithExpectedType ->
                 transformAnonymousFunctionWithExpectedType(anonymousFunction, data.expectedTypeRef, data)
-            is ResolutionMode.ContextIndependent, is ResolutionMode.AssignmentLValue, is ResolutionMode.ReceiverResolution ->
+
+            is ResolutionMode.ContextIndependent,
+            is ResolutionMode.AssignmentLValue,
+            is ResolutionMode.ReceiverResolution,
+            is ResolutionMode.Delegate,
+            ->
                 transformAnonymousFunctionWithExpectedType(anonymousFunction, FirImplicitTypeRefImplWithoutSource, data)
             is ResolutionMode.WithStatus ->
                 throw AssertionError("Should not be here in WithStatus/WithExpectedTypeFromCast mode")

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirExpressionsResolveTransformer.kt

@@ -491,10 +491,7 @@ open class FirExpressionsResolveTransformer(transformer: FirAbstractBodyResolveT
         )
 
         val approximationIsNeeded =
-            resolutionMode !is ResolutionMode.ReceiverResolution &&
+            resolutionMode !is ResolutionMode.ReceiverResolution && resolutionMode !is ResolutionMode.ContextDependent
-                    (resolutionMode !is ResolutionMode.ContextDependent ||
-                            // TODO check why we need a special case for ContextDependent.Delegate
-                            resolutionMode is ResolutionMode.ContextDependent.Delegate)
 
         val integerOperatorCall = buildIntegerLiteralOperatorCall {
             source = originalCall.source
@@ -1070,8 +1067,7 @@ open class FirExpressionsResolveTransformer(transformer: FirAbstractBodyResolveT
 
         transformedLHS?.let { callableReferenceAccess.replaceExplicitReceiver(transformedLHS) }
 
-        // TODO check why we need a special case for ContextDependent.Delegate
+        return if (data is ResolutionMode.ContextDependent) {
-        return if (data is ResolutionMode.ContextDependent && data !is ResolutionMode.ContextDependent.Delegate) {
             context.storeCallableReferenceContext(callableReferenceAccess)
             callableReferenceAccess
         } else {

compiler/testData/diagnostics/tests/delegatedProperty/inference/lambdaDelegate.kt

@@ -0,0 +1,38 @@
+// ISSUE: KT-64635
+// FIR_IDENTICAL
+import kotlin.reflect.KProperty
+
+class Context
+
+interface MyReadOnlyProperty<in T, out V> {
+    operator fun getValue(thisRef: T, property: KProperty<*>): V
+}
+
+open class NodeHolder {
+    operator fun ((Context).() -> Unit).provideDelegate(
+        thisRef: Any?,
+        prop: KProperty<*>
+    ): MyReadOnlyProperty<Any?, Unit> = TODO()
+}
+
+class SubClass1 : NodeHolder() {
+    val foo: (Context).() -> Unit = {}
+    val x by foo
+}
+
+class SubClass2 : NodeHolder() {
+    val x by <!DELEGATE_SPECIAL_FUNCTION_MISSING!>{}<!>
+}
+
+fun main() {
+    val my_holder_works =
+        object : NodeHolder() {
+            val foo: (Context).() -> Unit = {}
+            val x by foo
+        }
+
+    val my_holder_bad =
+        object : NodeHolder() {
+            val x by <!DELEGATE_SPECIAL_FUNCTION_MISSING!>{}<!>
+        }
+}

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

@@ -10687,6 +10687,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                     runTest("compiler/testData/diagnostics/tests/delegatedProperty/inference/labeledDelegatedExpression.kt");
                 }
 
+                @Test
+                @TestMetadata("lambdaDelegate.kt")
+                public void testLambdaDelegate() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/delegatedProperty/inference/lambdaDelegate.kt");
+                }
+
                 @Test
                 @TestMetadata("lambdaWithMultipleReturns.kt")
                 public void testLambdaWithMultipleReturns() throws Exception {