From 80ccf832531f9461462b7e4494363d911612da61 Mon Sep 17 00:00:00 2001
From: "Jurgen J. Vinju" <Jurgen.Vinju@cwi.nl>
Date: Thu, 10 Oct 2024 10:09:26 +0200
Subject: [PATCH] this fixes #2048

---
 .../interpreter/result/RelationResult.java          | 11 +++++++----
 .../library/lang/rascal/tests/basic/Relations.rsc   | 13 +++++++++++++
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/src/org/rascalmpl/interpreter/result/RelationResult.java b/src/org/rascalmpl/interpreter/result/RelationResult.java
index 196fec40206..76f7a205ef2 100644
--- a/src/org/rascalmpl/interpreter/result/RelationResult.java
+++ b/src/org/rascalmpl/interpreter/result/RelationResult.java
@@ -431,13 +431,16 @@ public Result<IValue> fieldSelect(Field[] selectedFields) {
 					fieldIndices[i] = ((IInteger) f.getFieldIndex()
 							.interpret(this.ctx.getEvaluator()).getValue()).intValue();
 				} else {
-					String fieldName = org.rascalmpl.interpreter.utils.Names
-							.name(f.getFieldName());
+					String fieldName = org.rascalmpl.interpreter.utils.Names.name(f.getFieldName());
+
+					if (!baseType.hasFieldNames()) {
+						throw new UndeclaredField(fieldName, baseType,ctx.getCurrentAST());
+					}
+
 					try {
 						fieldIndices[i] = baseType.getFieldIndex(fieldName);
 					} catch (UndeclaredFieldException e) {
-						throw new UndeclaredField(fieldName, baseType,
-								ctx.getCurrentAST());
+						throw new UndeclaredField(fieldName, baseType, ctx.getCurrentAST());
 					}
 				}
 
diff --git a/src/org/rascalmpl/library/lang/rascal/tests/basic/Relations.rsc b/src/org/rascalmpl/library/lang/rascal/tests/basic/Relations.rsc
index bfbae1e6403..459ef2588c4 100644
--- a/src/org/rascalmpl/library/lang/rascal/tests/basic/Relations.rsc
+++ b/src/org/rascalmpl/library/lang/rascal/tests/basic/Relations.rsc
@@ -108,3 +108,16 @@ test bool tst_rangeX(rel[int, int] X) {
    XR = rangeX(X, s);
    return isEmpty(XR) || all(<_, b> <- XR, b notin s);
 }
+
+@expected{UndeclaredField}
+@ignoreCompiler{The checker would detect this}
+test bool fieldSelectionNoFields() {
+   x = {};
+   x<name>; // throws UndeclaredField
+   return false;
+}
+
+test bool fieldSelectionEmpty() {
+   rel[int a, int b] x = {};
+   return x<b,a> == {};
+}
\ No newline at end of file