From 57c9a71b6004b9fc0ed6cc3c87f4d62141fc6d62 Mon Sep 17 00:00:00 2001
From: Kristóf Marussy <kristof@marussy.com>
Date: Mon, 6 Nov 2023 01:04:02 +0100
Subject: refactor(language): opposite content assist

Only show references that may plausibly appear in an opposite declaration.
---
 .../ProblemCrossrefProposalProvider.java           | 34 +++++++++++++++++++++-
 .../language/scoping/ProblemScopeProvider.java     | 15 ++++++----
 2 files changed, 42 insertions(+), 7 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 ||
diff --git a/subprojects/language/src/main/java/tools/refinery/language/scoping/ProblemScopeProvider.java b/subprojects/language/src/main/java/tools/refinery/language/scoping/ProblemScopeProvider.java
index cf099aba..a4437ba6 100644
--- a/subprojects/language/src/main/java/tools/refinery/language/scoping/ProblemScopeProvider.java
+++ b/subprojects/language/src/main/java/tools/refinery/language/scoping/ProblemScopeProvider.java
@@ -44,7 +44,7 @@ public class ProblemScopeProvider extends AbstractProblemScopeProvider {
 			return getVariableScope(context, scope);
 		}
 		if (reference == ProblemPackage.Literals.REFERENCE_DECLARATION__OPPOSITE) {
-			return getOppositeScope(context, scope);
+			return getOppositeScope(context);
 		}
 		return scope;
 	}
@@ -96,16 +96,19 @@ public class ProblemScopeProvider extends AbstractProblemScopeProvider {
 		}
 	}
 
-	protected IScope getOppositeScope(EObject context, IScope delegateScope) {
+	protected IScope getOppositeScope(EObject context) {
 		var referenceDeclaration = EcoreUtil2.getContainerOfType(context, ReferenceDeclaration.class);
 		if (referenceDeclaration == null) {
-			return delegateScope;
+			return IScope.NULLSCOPE;
 		}
 		var relation = referenceDeclaration.getReferenceType();
 		if (!(relation instanceof ClassDeclaration classDeclaration)) {
-			return delegateScope;
+			return IScope.NULLSCOPE;
 		}
-		var referenceDeclarations = desugarer.getAllReferenceDeclarations(classDeclaration);
-		return Scopes.scopeFor(referenceDeclarations, delegateScope);
+		var referenceDeclarations = classDeclaration.getFeatureDeclarations()
+				.stream()
+				.filter(ReferenceDeclaration.class::isInstance)
+				.toList();
+		return Scopes.scopeFor(referenceDeclarations);
 	}
 }
-- 
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