fix: allow usage of covariant type parameters in own constructor

packages/safe-ds-lang/src/language/helpers/nodeProperties.ts

@@ -1,6 +1,7 @@
 import { AstNode, getContainerOfType, Stream, stream } from 'langium';
 import {
     isSdsAnnotation,
+    isSdsArgument,
     isSdsArgumentList,
     isSdsAssignment,
     isSdsAttribute,
@@ -78,29 +79,29 @@ export const hasAnnotationCallOf = (
     });
 };
 
-export const isInternal = (node: SdsDeclaration): boolean => {
+export const isInternal = (node: SdsDeclaration | undefined): boolean => {
     return isSdsSegment(node) && node.visibility === 'internal';
 };
 
 export namespace Argument {
-    export const isNamed = (node: SdsArgument): boolean => {
-        return Boolean(node.parameter);
+    export const isNamed = (node: SdsArgument | undefined): boolean => {
+        return Boolean(node?.parameter);
     };
 
-    export const isPositional = (node: SdsArgument): boolean => {
-        return !node.parameter;
+    export const isPositional = (node: SdsArgument | undefined): boolean => {
+        return isSdsArgument(node) && !node.parameter;
     };
 }
 
 export namespace Enum {
-    export const isConstant = (node: SdsEnum): boolean => {
-        return getEnumVariants(node).every((it) => EnumVariant.isConstant(it));
+    export const isConstant = (node: SdsEnum | undefined): boolean => {
+        return Boolean(node) && getEnumVariants(node).every((it) => EnumVariant.isConstant(it));
     };
 }
 
 export namespace EnumVariant {
-    export const isConstant = (node: SdsEnumVariant): boolean => {
-        return getParameters(node).every((it) => Parameter.isConstant(it));
+    export const isConstant = (node: SdsEnumVariant | undefined): boolean => {
+        return Boolean(node) && getParameters(node).every((it) => Parameter.isConstant(it));
     };
 }
 
@@ -129,7 +130,7 @@ export namespace Parameter {
     };
 }
 
-export const isStatic = (node: SdsClassMember): boolean => {
+export const isStatic = (node: SdsClassMember | undefined): boolean => {
     if (isSdsClass(node) || isSdsEnum(node)) {
         return true;
     } else if (isSdsAttribute(node)) {
@@ -143,8 +144,8 @@ export const isStatic = (node: SdsClassMember): boolean => {
 };
 
 export namespace TypeArgument {
-    export const isNamed = (node: SdsTypeArgument): boolean => {
-        return Boolean(node.typeParameter);
+    export const isNamed = (node: SdsTypeArgument | undefined): boolean => {
+        return Boolean(node?.typeParameter);
     };
 }
 

packages/safe-ds-lang/src/language/validation/other/declarations/typeParameters.ts

@@ -87,10 +87,17 @@ export const typeParameterMustBeUsedInCorrectPosition = (services: SafeDsService
                     node: reference,
                     code: CODE_TYPE_PARAMETER_USAGE,
                 });
+                return; // Don't show other errors for this reference
+            }
+
+            // Usages in the **own constructor** are always correct. This check must come after the previous one, since
+            // that one filters out usages in **constructors of nested classes**.
+            if (isInConstructor(reference)) {
+                return;
             }
 
             // Check usage of variant type parameters
-            else if (TypeParameter.isContravariant(node)) {
+            if (TypeParameter.isContravariant(node)) {
                 const position = getTypePosition(nodeMapper, declarationWithTypeParameter, reference);
 
                 if (position !== 'contravariant') {
@@ -113,6 +120,11 @@ export const typeParameterMustBeUsedInCorrectPosition = (services: SafeDsService
     };
 };
 
+const isInConstructor = (node: AstNode) => {
+    const parameterList = getContainerOfType(node, isSdsParameterList);
+    return isSdsClass(parameterList?.$container);
+};
+
 const classTypeParameterIsUsedInCorrectPosition = (classWithTypeParameter: SdsClass, reference: AstNode) => {
     const containingClassMember = getContainerOfType(reference, isSdsClassMember);
 
@@ -121,7 +133,7 @@ const classTypeParameterIsUsedInCorrectPosition = (classWithTypeParameter: SdsCl
         return true;
     }
 
-    // Handle usage in static context
+    // Handle usage in static member
     if (isStatic(containingClassMember)) {
         return false;
     }

packages/safe-ds-lang/tests/resources/validation/other/declarations/type parameters/usage of variant type parameter/covariant type parameter.sdstest

@@ -1,6 +1,6 @@
 package tests.validation.other.declarations.typeParameters.usageOfVariantTypeParameters
 
-// $TEST$ error "A covariant type parameter cannot be used in contravariant position."
+// $TEST$ no error r"A .*variant type parameter cannot be used in .*variant position."
 class MyClass2<out Covariant>(p1: »Covariant«) {
     // $TEST$ no error r"A .*variant type parameter cannot be used in .*variant position."
     attr a1: »Covariant«