feat: various features related to literal types (#657)

Closes partially #80

### Summary of Changes

* Show an error if literal types have no literals
* Show an error if lists or maps are used in a literal types
* Mark literal types as experimental (show a warning when they are used)
* Compute type of manifest literal types
* Evaluate literals to a literal type instead of the corresponding
class. For example, the literal `1` now gets the type `literal<1>`
instead of `Int`).

---------

Co-authored-by: megalinter-bot <129584137+megalinter-bot@users.noreply.github.com>

src/language/safe-ds-module.ts

@@ -24,6 +24,8 @@ import { SafeDsAnnotations } from './builtins/safe-ds-annotations.js';
 import { SafeDsClassHierarchy } from './typing/safe-ds-class-hierarchy.js';
 import { SafeDsPartialEvaluator } from './partialEvaluation/safe-ds-partial-evaluator.js';
 import { SafeDsSemanticTokenProvider } from './lsp/safe-ds-semantic-token-provider.js';
+import { SafeDsTypeChecker } from './typing/safe-ds-type-checker.js';
+import { SafeDsCoreTypes } from './typing/safe-ds-core-types.js';
 
 /**
  * Declaration of custom services - add your own service classes here.
@@ -41,6 +43,8 @@ export type SafeDsAddedServices = {
     };
     types: {
         ClassHierarchy: SafeDsClassHierarchy;
+        CoreTypes: SafeDsCoreTypes;
+        TypeChecker: SafeDsTypeChecker;
         TypeComputer: SafeDsTypeComputer;
     };
     workspace: {
@@ -83,6 +87,8 @@ export const SafeDsModule: Module<SafeDsServices, PartialLangiumServices & SafeD
     },
     types: {
         ClassHierarchy: (services) => new SafeDsClassHierarchy(services),
+        CoreTypes: (services) => new SafeDsCoreTypes(services),
+        TypeChecker: (services) => new SafeDsTypeChecker(services),
         TypeComputer: (services) => new SafeDsTypeComputer(services),
     },
     workspace: {

src/language/typing/model.ts

@@ -1,14 +1,13 @@
 import {
-    isSdsNull,
     SdsAbstractResult,
     SdsCallable,
     SdsClass,
     SdsDeclaration,
     SdsEnum,
     SdsEnumVariant,
-    SdsLiteral,
     SdsParameter,
 } from '../generated/ast.js';
+import { Constant, NullConstant } from '../partialEvaluation/model.js';
 
 /* c8 ignore start */
 export abstract class Type {
@@ -68,10 +67,10 @@ export class CallableType extends Type {
 export class LiteralType extends Type {
     override readonly isNullable: boolean;
 
-    constructor(readonly values: SdsLiteral[]) {
+    constructor(readonly constants: Constant[]) {
         super();
 
-        this.isNullable = values.some(isSdsNull);
+        this.isNullable = constants.some((it) => it === NullConstant);
     }
 
     override copyWithNullability(isNullable: boolean): LiteralType {
@@ -93,11 +92,15 @@ export class LiteralType extends Type {
             return false;
         }
 
-        throw Error('Not implemented');
+        if (other.constants.length !== this.constants.length) {
+            return false;
+        }
+
+        return other.constants.every((otherValue) => this.constants.some((value) => value.equals(otherValue)));
     }
 
     override toString(): string {
-        throw Error('Not implemented');
+        return `literal<${this.constants.join(', ')}>`;
     }
 }
 
@@ -300,10 +303,12 @@ export class StaticType extends Type {
 }
 
 export class UnionType extends Type {
-    override readonly isNullable = false;
+    override readonly isNullable: boolean;
 
     constructor(readonly possibleTypes: Type[]) {
         super();
+
+        this.isNullable = possibleTypes.some((it) => it.isNullable);
     }
 
     override copyWithNullability(_isNullable: boolean): UnionType {

src/language/typing/safe-ds-class-hierarchy.ts

@@ -16,9 +16,26 @@ export class SafeDsClassHierarchy {
     }
 
     /**
-     * Returns a stream of all superclasses of the given class. The class itself is not included in the stream unless
-     * there is a cycle in the inheritance hierarchy. Direct ancestors are returned first, followed by their ancestors
-     * and so on.
+     * Returns `true` if the given node is equal to or a subclass of the given other node. If one of the nodes is
+     * undefined, `false` is returned.
+     */
+    isEqualToOrSubclassOf(node: SdsClass | undefined, other: SdsClass | undefined): boolean {
+        if (!node || !other) {
+            return false;
+        }
+
+        // Nothing is a subclass of everything
+        if (node === this.builtinClasses.Nothing) {
+            return true;
+        }
+
+        return node === other || this.streamSuperclasses(node).includes(other);
+    }
+
+    /**
+     * Returns a stream of all superclasses of the given class. Direct ancestors are returned first, followed by their
+     * ancestors and so on. The class itself is not included in the stream unless there is a cycle in the inheritance
+     * hierarchy.
      */
     streamSuperclasses(node: SdsClass | undefined): Stream<SdsClass> {
         if (!node) {
@@ -58,3 +75,22 @@ export class SafeDsClassHierarchy {
         return undefined;
     }
 }
+
+// fun SdsClass.superClassMembers() =
+//     this.superClasses().flatMap { it.classMembersOrEmpty().asSequence() }
+//
+// // TODO only static methods can be hidden
+// fun SdsFunction.hiddenFunction(): SdsFunction? {
+//     val containingClassOrInterface = closestAncestorOrNull<SdsClass>() ?: return null
+//     return containingClassOrInterface.superClassMembers()
+//         .filterIsInstance<SdsFunction>()
+//         .firstOrNull { it.name == name }
+// }
+//
+// fun SdsClass?.inheritedNonStaticMembersOrEmpty(): Set<SdsAbstractDeclaration> {
+//     return this?.parentClassesOrEmpty()
+//         ?.flatMap { it.classMembersOrEmpty() }
+// ?.filter { it is SdsAttribute && !it.isStatic || it is SdsFunction && !it.isStatic }
+// ?.toSet()
+//     .orEmpty()
+// }

src/language/typing/safe-ds-core-types.ts

@@ -0,0 +1,60 @@
+import { WorkspaceCache } from 'langium';
+import { SafeDsServices } from '../safe-ds-module.js';
+import { SafeDsClasses } from '../builtins/safe-ds-classes.js';
+import { ClassType, Type, UnknownType } from './model.js';
+import { SdsClass } from '../generated/ast.js';
+
+export class SafeDsCoreTypes {
+    private readonly builtinClasses: SafeDsClasses;
+    private readonly cache: WorkspaceCache<string, Type>;
+
+    constructor(services: SafeDsServices) {
+        this.builtinClasses = services.builtins.Classes;
+        this.cache = new WorkspaceCache(services.shared);
+    }
+
+    get AnyOrNull(): Type {
+        return this.createCoreType(this.builtinClasses.Any, true);
+    }
+
+    get Boolean(): Type {
+        return this.createCoreType(this.builtinClasses.Boolean);
+    }
+
+    get Float(): Type {
+        return this.createCoreType(this.builtinClasses.Float);
+    }
+
+    get Int(): Type {
+        return this.createCoreType(this.builtinClasses.Int);
+    }
+
+    get List(): Type {
+        return this.createCoreType(this.builtinClasses.List);
+    }
+
+    get Map(): Type {
+        return this.createCoreType(this.builtinClasses.Map);
+    }
+
+    /* c8 ignore start */
+    get NothingOrNull(): Type {
+        return this.createCoreType(this.builtinClasses.Nothing, true);
+    }
+    /* c8 ignore stop */
+
+    get String(): Type {
+        return this.createCoreType(this.builtinClasses.String);
+    }
+
+    private createCoreType(coreClass: SdsClass | undefined, isNullable: boolean = false): Type {
+        /* c8 ignore start */
+        if (!coreClass) {
+            return UnknownType;
+        }
+        /* c8 ignore stop */
+
+        const key = `${coreClass.name}~${isNullable}`;
+        return this.cache.get(key, () => new ClassType(coreClass, isNullable));
+    }
+}