[FE] KT-50878 Prohibit using contextual declarations without -Xcontext-receivers

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -1299,6 +1299,7 @@ public interface Errors {
     DiagnosticFactory1<KtElement, String> NO_CONTEXT_RECEIVER = DiagnosticFactory1.create(ERROR);
     DiagnosticFactory1<KtElement, String> MULTIPLE_ARGUMENTS_APPLICABLE_FOR_CONTEXT_RECEIVER = DiagnosticFactory1.create(ERROR);
     DiagnosticFactory0<KtElement> AMBIGUOUS_CALL_WITH_IMPLICIT_CONTEXT_RECEIVER = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<KtElement> UNSUPPORTED_CONTEXTUAL_DECLARATION_CALL = DiagnosticFactory0.create(ERROR);
 
     // Error sets
     ImmutableSet<? extends DiagnosticFactory<?>> UNRESOLVED_REFERENCE_DIAGNOSTICS = ImmutableSet.of(

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -1109,6 +1109,7 @@ public class DefaultErrorMessages {
         MAP.put(NO_CONTEXT_RECEIVER, "No required context receiver found: {0}", TO_STRING);
         MAP.put(MULTIPLE_ARGUMENTS_APPLICABLE_FOR_CONTEXT_RECEIVER, "Multiple arguments applicable for context receiver: {0}", TO_STRING);
         MAP.put(AMBIGUOUS_CALL_WITH_IMPLICIT_CONTEXT_RECEIVER, "With implicit context receiver, call is ambiguous. Specify the receiver explicitly");
+        MAP.put(UNSUPPORTED_CONTEXTUAL_DECLARATION_CALL, "To use contextual declarations, specify the `-Xcontext-receivers` compiler option");
 
         MAP.setImmutable();
 

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/DiagnosticReporterByTrackingStrategy.kt

@@ -132,6 +132,10 @@ class DiagnosticReporterByTrackingStrategy(
                 val callElement = psiKotlinCall.psiCall.callElement
                 trace.report(AMBIGUOUS_CALL_WITH_IMPLICIT_CONTEXT_RECEIVER.on(callElement))
             }
+            UnsupportedContextualDeclarationCall::class.java -> {
+                val callElement = psiKotlinCall.psiCall.callElement
+                trace.report(UNSUPPORTED_CONTEXTUAL_DECLARATION_CALL.on(callElement))
+            }
         }
     }