4 files changed, 148 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);
+        }
+}
diff --git a/language-model/src/main/java/tools/refinery/language/model/ProblemUtil.java b/language-model/src/main/java/tools/refinery/language/model/ProblemUtil.java
index b6b199f8..5f8641bf 100644
--- a/language-model/src/main/java/tools/refinery/language/model/ProblemUtil.java
+++ b/language-model/src/main/java/tools/refinery/language/model/ProblemUtil.java
@@ -12,6 +12,7 @@ import org.eclipse.emf.ecore.EObject;
 import org.eclipse.emf.ecore.resource.Resource;
 
 import tools.refinery.language.model.problem.ClassDeclaration;
+import tools.refinery.language.model.problem.ImplicitVariable;
 import tools.refinery.language.model.problem.Node;
 import tools.refinery.language.model.problem.Problem;
 import tools.refinery.language.model.problem.ProblemPackage;
@@ -33,6 +34,24 @@ public final class ProblemUtil {
         public static boolean isSingletonVariable(Variable variable) {
                 return variable.eContainingFeature() == ProblemPackage.Literals.VARIABLE_OR_NODE_ARGUMENT__SINGLETON_VARIABLE;
         }
+        
+        public static boolean isImplicitVariable(Variable variable) {
+                return variable instanceof ImplicitVariable;
+        }
+        
+        public static boolean isImplicitNode(Node node) {
+                return node.eContainingFeature() == ProblemPackage.Literals.PROBLEM__NODES;
+        }
+        
+        public static boolean isImplicit(EObject eObject) {
+                if (eObject instanceof Node node) {
+                        return isImplicitNode(node);
+                } else if (eObject instanceof Variable variable) {
+                        return isImplicitVariable(variable);
+                } else {
+                        return false;
+                }
+        }
 
         public static boolean isUniqueNode(Node node) {
                 var containingFeature = node.eContainingFeature();
diff --git a/language/src/main/java/tools/refinery/language/resource/ReferenceCounter.java b/language/src/main/java/tools/refinery/language/resource/ReferenceCounter.java
new file mode 100644
index 00000000..56186bc9
--- /dev/null
+++ b/language/src/main/java/tools/refinery/language/resource/ReferenceCounter.java
@@ -0,0 +1,43 @@
+package tools.refinery.language.resource;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.eclipse.emf.ecore.EObject;
+import org.eclipse.xtext.util.IResourceScopeCache;
+
+import com.google.inject.Inject;
+import com.google.inject.Singleton;
+
+import tools.refinery.language.model.problem.Problem;
+
+@Singleton
+public class ReferenceCounter {
+        @Inject
+        private IResourceScopeCache cache;
+
+        public Map<EObject, Integer> getReferenceCounts(Problem problem) {
+                var resource = problem.eResource();
+                if (resource == null) {
+                        return doGetReferenceCounts(problem);
+                }
+                return cache.get(problem, resource, () -> doGetReferenceCounts(problem));
+        }
+
+        protected Map<EObject, Integer> doGetReferenceCounts(Problem problem) {
+                var map = new HashMap<EObject, Integer>();
+                countCrossReferences(problem, map);
+                var iterator = problem.eAllContents();
+                while (iterator.hasNext()) {
+                        var eObject = iterator.next();
+                        countCrossReferences(eObject, map);
+                }
+                return map;
+        }
+
+        protected void countCrossReferences(EObject eObject, Map<EObject, Integer> map) {
+                for (var referencedObject : eObject.eCrossReferences()) {
+                        map.compute(referencedObject, (key, currentValue) -> currentValue == null ? 1 : currentValue + 1);
+                }
+        }
+}