2 files changed, 86 insertions, 1 deletions

diff --git a/language-ide/src/main/java/tools/refinery/language/ide/ProblemIdeModule.java b/language-ide/src/main/java/tools/refinery/language/ide/ProblemIdeModule.java
index 3502c29f..51cecf06 100644
--- a/language-ide/src/main/java/tools/refinery/language/ide/ProblemIdeModule.java
+++ b/language-ide/src/main/java/tools/refinery/language/ide/ProblemIdeModule.java
@@ -4,9 +4,11 @@
 package tools.refinery.language.ide;
 
 import org.eclipse.xtext.ide.editor.contentassist.IPrefixMatcher;
+import org.eclipse.xtext.ide.editor.contentassist.IdeCrossrefProposalProvider;
 import org.eclipse.xtext.ide.editor.syntaxcoloring.ISemanticHighlightingCalculator;
 
 import tools.refinery.language.ide.contentassist.FuzzyMatcher;
+import tools.refinery.language.ide.contentassist.ProblemCrossrefProposalProvider;
 import tools.refinery.language.ide.syntaxcoloring.ProblemSemanticHighlightingCalculator;
 
 /**
@@ -16,9 +18,13 @@ public class ProblemIdeModule extends AbstractProblemIdeModule {
         public Class<? extends ISemanticHighlightingCalculator> bindISemanticHighlightingCalculator() {
                 return ProblemSemanticHighlightingCalculator.class;
         }
-        
+
         @Override
         public Class<? extends IPrefixMatcher> bindIPrefixMatcher() {
                 return FuzzyMatcher.class;
         }
+
+        public Class<? extends IdeCrossrefProposalProvider> bindIdeCrossrefProposalProvider() {
+                return ProblemCrossrefProposalProvider.class;
+        }
 }
diff --git a/language-ide/src/main/java/tools/refinery/language/ide/contentassist/ProblemCrossrefProposalProvider.java b/language-ide/src/main/java/tools/refinery/language/ide/contentassist/ProblemCrossrefProposalProvider.java
new file mode 100644
index 00000000..416535ce
--- /dev/null
+++ b/language-ide/src/main/java/tools/refinery/language/ide/contentassist/ProblemCrossrefProposalProvider.java
@@ -0,0 +1,79 @@
+package tools.refinery.language.ide.contentassist;
+
+import java.util.Objects;
+
+import org.eclipse.emf.ecore.EObject;
+import org.eclipse.emf.ecore.util.EcoreUtil;
+import org.eclipse.xtext.CrossReference;
+import org.eclipse.xtext.GrammarUtil;
+import org.eclipse.xtext.ide.editor.contentassist.ContentAssistContext;
+import org.eclipse.xtext.ide.editor.contentassist.ContentAssistEntry;
+import org.eclipse.xtext.ide.editor.contentassist.IdeCrossrefProposalProvider;
+import org.eclipse.xtext.nodemodel.util.NodeModelUtils;
+import org.eclipse.xtext.resource.IEObjectDescription;
+
+import com.google.inject.Inject;
+
+import tools.refinery.language.model.ProblemUtil;
+import tools.refinery.language.model.problem.Problem;
+import tools.refinery.language.resource.ReferenceCounter;
+
+public class ProblemCrossrefProposalProvider extends IdeCrossrefProposalProvider {
+        @Inject
+        private ReferenceCounter referenceCounter;
+
+        @Override
+        protected ContentAssistEntry createProposal(IEObjectDescription candidate, CrossReference crossRef,
+                        ContentAssistContext context) {
+                if (!shouldCreateProposal(candidate, crossRef, context)) {
+                        return null;
+                }
+                return super.createProposal(candidate, crossRef, context);
+        }
+
+        protected boolean shouldCreateProposal(IEObjectDescription candidate, CrossReference crossRef,
+                        ContentAssistContext context) {
+                var rootModel = context.getRootModel();
+                var eObjectOrProxy = candidate.getEObjectOrProxy();
+                if (!Objects.equals(rootModel.eResource(), eObjectOrProxy.eResource())) {
+                        return true;
+                }
+                var currentValue = getCurrentValue(crossRef, context);
+                if (currentValue == null) {
+                        return true;
+                }
+                var eObject = EcoreUtil.resolve(eObjectOrProxy, rootModel);
+                if (!Objects.equals(currentValue, eObject)) {
+                        return true;
+                }
+                if (!ProblemUtil.isImplicit(eObject)) {
+                        return true;
+                }
+                if (rootModel instanceof Problem problem) {
+                        var referenceCounts = referenceCounter.getReferenceCounts(problem);
+                        var count = referenceCounts.get(eObject);
+                        return count != null && count >= 2;
+                }
+                return true;
+        }
+
+        protected EObject getCurrentValue(CrossReference crossRef, ContentAssistContext context) {
+                var value = getCurrentValue(crossRef, context.getCurrentModel());
+                if (value != null) {
+                        return value;
+                }
+                var currentNodeSemanticObject = NodeModelUtils.findActualSemanticObjectFor(context.getCurrentNode());
+                return getCurrentValue(crossRef, currentNodeSemanticObject);
+        }
+
+        protected EObject getCurrentValue(CrossReference crossRef, EObject context) {
+                if (context == null) {
+                        return null;
+                }
+                var eReference = GrammarUtil.getReference(crossRef, context.eClass());
+                if (eReference == null || eReference.isMany()) {
+                        return null;
+                }
+                return (EObject) context.eGet(eReference);
+        }
+}