[FE] Fix: do not report ambiguous label if label map is empty

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

@@ -10654,6 +10654,12 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                     runTest("compiler/testData/diagnostics/tests/extensions/contextReceivers/insideDeclaration.kt");
                 }
 
+                @Test
+                @TestMetadata("labelFromFunctionName.kt")
+                public void testLabelFromFunctionName() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/extensions/contextReceivers/labelFromFunctionName.kt");
+                }
+
                 @Test
                 @TestMetadata("labelsFromClassNameForbidden.kt")
                 public void testLabelsFromClassNameForbidden() throws Exception {

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

@@ -10654,6 +10654,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                     runTest("compiler/testData/diagnostics/tests/extensions/contextReceivers/insideDeclaration.kt");
                 }
 
+                @Test
+                @TestMetadata("labelFromFunctionName.kt")
+                public void testLabelFromFunctionName() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/extensions/contextReceivers/labelFromFunctionName.kt");
+                }
+
                 @Test
                 @TestMetadata("labelsFromClassNameForbidden.kt")
                 public void testLabelsFromClassNameForbidden() throws Exception {

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

@@ -10654,6 +10654,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                     runTest("compiler/testData/diagnostics/tests/extensions/contextReceivers/insideDeclaration.kt");
                 }
 
+                @Test
+                @TestMetadata("labelFromFunctionName.kt")
+                public void testLabelFromFunctionName() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/extensions/contextReceivers/labelFromFunctionName.kt");
+                }
+
                 @Test
                 @TestMetadata("labelsFromClassNameForbidden.kt")
                 public void testLabelsFromClassNameForbidden() throws Exception {

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/LabelResolver.kt

@@ -190,7 +190,7 @@ object LabelResolver {
                     ]
                     val thisReceivers = labelNameToReceiverMap?.get(labelName.identifier)
                     val thisReceiver = when {
-                        thisReceivers == null -> declarationDescriptor.extensionReceiverParameter
+                        thisReceivers.isNullOrEmpty() -> declarationDescriptor.extensionReceiverParameter
                         thisReceivers.size == 1 -> thisReceivers.single()
                         else -> {
                             BindingContextUtils.reportAmbiguousLabel(context.trace, targetLabel, declarationsByLabel)

compiler/testData/diagnostics/tests/extensions/contextReceivers/labelFromFunctionName.kt

@@ -0,0 +1,9 @@
+// FIR_IDENTICAL
+// !LANGUAGE: +ContextReceivers
+// WITH_STDLIB
+
+fun testLabels(source: Collection<String>) {
+    val r = buildList {
+        source.mapTo(this@buildList) { it.length }
+    }
+}

compiler/testData/diagnostics/tests/extensions/contextReceivers/labelFromFunctionName.txt

@@ -0,0 +1,3 @@
+package
+
+public fun testLabels(/*0*/ source: kotlin.collections.Collection<kotlin.String>): kotlin.Unit

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

@@ -10660,6 +10660,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                     runTest("compiler/testData/diagnostics/tests/extensions/contextReceivers/insideDeclaration.kt");
                 }
 
+                @Test
+                @TestMetadata("labelFromFunctionName.kt")
+                public void testLabelFromFunctionName() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/extensions/contextReceivers/labelFromFunctionName.kt");
+                }
+
                 @Test
                 @TestMetadata("labelsFromClassNameForbidden.kt")
                 public void testLabelsFromClassNameForbidden() throws Exception {