Check for duplicate named params in function type

2 files changed, 34 insertions, 0 deletions

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index 3dd5e138..d7ad4627 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -651,6 +651,16 @@ public class TypeChecker {
             })
             .toList();
 
+        var seenParamNames = new HashSet<String>();
+        for (var untypedParamNode : untyped.params().named()) {
+            if (!seenParamNames.add(untypedParamNode.name())) {
+                throw new DuplicateVariableName(
+                    untypedParamNode.name(),
+                    untypedParamNode.source()
+                );
+            }
+        }
+
         var effect = untyped.effect()
             .map(untypedEffect -> typeCheckTypeLevelExpression(
                 TypeSets.EFFECT,
diff --git a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerFunctionTypeTests.java b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerFunctionTypeTests.java
index 6b48a604..12022314 100644
--- a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerFunctionTypeTests.java
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerFunctionTypeTests.java
@@ -3,6 +3,7 @@ package org.shedlang.compiler.typechecker;
 import org.junit.jupiter.api.Test;
 import org.shedlang.compiler.ast.untyped.Untyped;
 import org.shedlang.compiler.ast.untyped.UntypedFunctionTypeNode;
+import org.shedlang.compiler.typechecker.errors.DuplicateVariableName;
 import org.shedlang.compiler.typechecker.typesets.TypeSets;
 import org.shedlang.compiler.types.Effects;
 import org.shedlang.compiler.types.FunctionType;
@@ -11,6 +12,7 @@ import org.shedlang.compiler.util.P;
 
 import java.util.Map;
 
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.shedlang.compiler.ast.typed.TypedNodeMatchers.isTypedFunctionTypeNode;
 import static org.zwobble.precisely.AssertThat.assertThat;
 import static org.zwobble.precisely.Matchers.equalTo;
@@ -141,4 +143,26 @@ public class TypeCheckerFunctionTypeTests {
             ))
         );
     }
+
+    @Test
+    public void whenNamedParamsHaveSameNameThenErrorIsThrown() {
+        var untyped = UntypedFunctionTypeNode.builder()
+            .addNamedParam("a", Untyped.typeLevelReference("Int"))
+            .addNamedParam("a", Untyped.typeLevelReference("Bool"))
+            .withReturnType(Untyped.typeLevelReference("String"))
+            .build();
+        var context = TypeCheckerContext.EMPTY
+            .enterGlobal(P.map(
+                Map.entry("Bool", Types.metaType(Types.BOOL)),
+                Map.entry("Int", Types.metaType(Types.INT)),
+                Map.entry("String", Types.metaType(Types.STRING))
+            ));
+
+        var error = assertThrows(
+            DuplicateVariableName.class,
+            () -> TypeChecker.typeCheckTypeLevelExpression(TypeSets.META_TYPE, untyped, context)
+        );
+
+        assertThat(error.variableName(), equalTo("a"));
+    }
 }