[K2]: compiler crash on unresolved delegated extention receiver

A report of UNRESOLVED_REFERENCE should not be made for elements like
FirImplicitThisReference that don't have a source, as they are implicit.

#KT-65044 Fixed

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

@@ -404,6 +404,12 @@ public class DiagnosticCompilerTestFirTestdataTestGenerated extends AbstractDiag
             runTest("compiler/fir/analysis-tests/testData/resolve/javaStaticScopeInheritance.kt");
         }
 
+        @Test
+        @TestMetadata("KT-65044.kt")
+        public void testKT_65044() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/resolve/KT-65044.kt");
+        }
+
         @Test
         @TestMetadata("kt41984.kt")
         public void testKt41984() throws Exception {

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

@@ -404,6 +404,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFirTestDataTestGenerated
             runTest("compiler/fir/analysis-tests/testData/resolve/javaStaticScopeInheritance.kt");
         }
 
+        @Test
+        @TestMetadata("KT-65044.kt")
+        public void testKT_65044() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/resolve/KT-65044.kt");
+        }
+
         @Test
         @TestMetadata("kt41984.kt")
         public void testKt41984() throws Exception {

compiler/fir/analysis-tests/testData/resolve/KT-65044.fir.txt

@@ -0,0 +1,5 @@
+FILE: KT-65044.kt
+    public final val <ERROR TYPE REF: Symbol not found for A>.b: <ERROR TYPE REF: Symbol not found for A?>by <Unresolved name: A>#.<Unresolved name: test>#()
+        public get(): <ERROR TYPE REF: Symbol not found for A?> {
+            ^ D|/b|.<Unresolved name: getValue>#(this@R|/b|, ::R|/b|)
+        }

compiler/fir/analysis-tests/testData/resolve/KT-65044.kt

@@ -0,0 +1 @@
+val <!UNRESOLVED_REFERENCE!>A<!>.b: <!UNRESOLVED_REFERENCE, UNRESOLVED_REFERENCE!>A<!>? by <!UNRESOLVED_REFERENCE!>A<!>.test()

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

@@ -404,6 +404,12 @@ public class FirLightTreeDiagnosticsTestGenerated extends AbstractFirLightTreeDi
             runTest("compiler/fir/analysis-tests/testData/resolve/javaStaticScopeInheritance.kt");
         }
 
+        @Test
+        @TestMetadata("KT-65044.kt")
+        public void testKT_65044() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/resolve/KT-65044.kt");
+        }
+
         @Test
         @TestMetadata("kt41984.kt")
         public void testKt41984() throws Exception {

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

@@ -404,6 +404,12 @@ public class FirPsiDiagnosticTestGenerated extends AbstractFirPsiDiagnosticTest
             runTest("compiler/fir/analysis-tests/testData/resolve/javaStaticScopeInheritance.kt");
         }
 
+        @Test
+        @TestMetadata("KT-65044.kt")
+        public void testKT_65044() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/resolve/KT-65044.kt");
+        }
+
         @Test
         @TestMetadata("kt41984.kt")
         public void testKt41984() throws Exception {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/coneDiagnosticToFirDiagnostic.kt

@@ -59,15 +59,23 @@ private fun ConeDiagnostic.toKtDiagnostic(
     is ConeUnresolvedSymbolError -> FirErrors.UNRESOLVED_REFERENCE.createOn(source, this.classId.asString(), null)
     is ConeUnresolvedNameError -> FirErrors.UNRESOLVED_REFERENCE.createOn(source, name.asString(), operatorToken)
     is ConeUnresolvedTypeQualifierError -> {
-        if (source?.kind == KtRealSourceElementKind) {
+        when {
+            // There could be an implicit reference here, such as FirImplicitThisReference,
+            // or other implicit elements without a source.
+            // In that case, it's not necessary to report UNRESOLVED_REFERENCE because they are implicit.
+            source == null -> null
+
             // this.qualifiers will contain all resolved qualifiers from the left up to (including) the first unresolved qualifier.
             // We want to report UNRESOLVED_REFERENCE exactly on the first unresolved qualifier with its name as argument.
             // Examples: <!UNRESOLVED_REFERENCE!>Unresolved<!>, <!UNRESOLVED_REFERENCE!>Unresolved<!>.Foo,
             // Resolved.<!UNRESOLVED_REFERENCE!>Unresolved<!>, Resolved.<!UNRESOLVED_REFERENCE!>Unresolved<!>.Foo
-            val lastQualifier = this.qualifiers.last()
-            FirErrors.UNRESOLVED_REFERENCE.createOn(lastQualifier.source, lastQualifier.name.asString(), null)
-        } else {
-            FirErrors.UNRESOLVED_REFERENCE.createOn(source, this.qualifier, null)
+            source.kind == KtRealSourceElementKind -> {
+                val lastQualifier = this.qualifiers.last()
+                FirErrors.UNRESOLVED_REFERENCE.createOn(lastQualifier.source, lastQualifier.name.asString(), null)
+            }
+            else -> {
+                FirErrors.UNRESOLVED_REFERENCE.createOn(source, this.qualifier, null)
+            }
         }
     }
     is ConeFunctionCallExpectedError -> FirErrors.FUNCTION_CALL_EXPECTED.createOn(source, this.name.asString(), this.hasValueParameters)