1 files changed, 33 insertions, 1 deletions

diff --git a/subprojects/language-ide/src/main/java/tools/refinery/language/ide/contentassist/ProblemCrossrefProposalProvider.java b/subprojects/language-ide/src/main/java/tools/refinery/language/ide/contentassist/ProblemCrossrefProposalProvider.java
index 8c787dfd..27e936a1 100644
--- a/subprojects/language-ide/src/main/java/tools/refinery/language/ide/contentassist/ProblemCrossrefProposalProvider.java
+++ b/subprojects/language-ide/src/main/java/tools/refinery/language/ide/contentassist/ProblemCrossrefProposalProvider.java
@@ -11,6 +11,7 @@ import org.eclipse.emf.ecore.EObject;
 import org.eclipse.emf.ecore.EReference;
 import org.eclipse.emf.ecore.util.EcoreUtil;
 import org.eclipse.xtext.CrossReference;
+import org.eclipse.xtext.EcoreUtil2;
 import org.eclipse.xtext.GrammarUtil;
 import org.eclipse.xtext.ide.editor.contentassist.ContentAssistContext;
 import org.eclipse.xtext.ide.editor.contentassist.IdeCrossrefProposalProvider;
@@ -105,14 +106,45 @@ public class ProblemCrossrefProposalProvider extends IdeCrossrefProposalProvider
                         return true;
                 }
 
+                var candidateEObjectOrProxy = candidate.getEObjectOrProxy();
+
+                if (eReference.equals(ProblemPackage.Literals.REFERENCE_DECLARATION__OPPOSITE) &&
+                                candidateEObjectOrProxy instanceof ReferenceDeclaration candidateReferenceDeclaration) {
+                        return oppositeShouldBeVisible(candidateReferenceDeclaration, context);
+                }
+
                 var builtinSymbolsOption = desugarer.getBuiltinSymbols(context.getRootModel());
                 if (builtinSymbolsOption.isEmpty()) {
                         return true;
                 }
                 var builtinSymbols = builtinSymbolsOption.get();
 
-                var candidateEObjectOrProxy = candidate.getEObjectOrProxy();
+                return builtinSymbolAwareShouldBeVisible(candidate, context, eReference, builtinSymbols,
+                                candidateEObjectOrProxy);
+        }
+
+        private static boolean oppositeShouldBeVisible(ReferenceDeclaration candidateReferenceDeclaration,
+                                                                                                   ContentAssistContext context) {
+                var referenceDeclaration = EcoreUtil2.getContainerOfType(context.getCurrentModel(),
+                                ReferenceDeclaration.class);
+                if (referenceDeclaration == null) {
+                        return true;
+                }
+                var classDeclaration = EcoreUtil2.getContainerOfType(referenceDeclaration, ClassDeclaration.class);
+                if (classDeclaration == null) {
+                        return true;
+                }
+                var oppositeType = candidateReferenceDeclaration.getReferenceType();
+                if (oppositeType == null) {
+                        return true;
+                }
+                var resolvedOppositeType = EcoreUtil.resolve(oppositeType, candidateReferenceDeclaration);
+                return classDeclaration.equals(resolvedOppositeType);
+        }
 
+        private boolean builtinSymbolAwareShouldBeVisible(
+                        IEObjectDescription candidate, ContentAssistContext context, EReference eReference,
+                        BuiltinSymbols builtinSymbols, EObject candidateEObjectOrProxy) {
                 if (eReference.equals(ProblemPackage.Literals.REFERENCE_DECLARATION__REFERENCE_TYPE) &&
                                 context.getCurrentModel() instanceof ReferenceDeclaration referenceDeclaration &&
                                 (referenceDeclaration.getKind() == ReferenceKind.CONTAINMENT ||