feat: stricter definition of const parameters (#776)

### Summary of Changes

The definition of `const` parameters is now more strict:
* Previously, any value that could be fully evaluated by the partial
evaluator could be assigned to a constant parameter.
* Now, a whitelist of expressions is allowed, including
    * boolean/float/int/null/string literals,
    * list literals (where the elements are constant),
    * map literals (where keys and values are constant),
    * enum variants (where arguments are constant).

This allows such parameters to be handled fully in the sidebar of the
graphical view. It also makes it possible to show errors/warnings at the
exact places they occur, like when checking whether an
`AnnotationTarget` appears multiple times.

packages/safe-ds-lang/src/language/partialEvaluation/safe-ds-partial-evaluator.ts

@@ -72,6 +72,10 @@ export class SafeDsPartialEvaluator {
         this.cache = new WorkspaceCache(services.shared);
     }
 
+    // -----------------------------------------------------------------------------------------------------------------
+    // evaluate
+    // -----------------------------------------------------------------------------------------------------------------
+
     evaluate(node: AstNode | undefined): EvaluatedNode {
         return this.evaluateWithSubstitutions(node, NO_SUBSTITUTIONS)?.unwrap();
     }
@@ -501,6 +505,46 @@ export class SafeDsPartialEvaluator {
     // else -> undefined
     // }
     // }
+
+    // -----------------------------------------------------------------------------------------------------------------
+    // canBeValueOfConstantParameter
+    // -----------------------------------------------------------------------------------------------------------------
+
+    /**
+     * Returns whether the given expression can be the value of a constant parameter.
+     */
+    canBeValueOfConstantParameter = (node: SdsExpression): boolean => {
+        if (isSdsBoolean(node) || isSdsFloat(node) || isSdsInt(node) || isSdsNull(node) || isSdsString(node)) {
+            return true;
+        } else if (isSdsCall(node)) {
+            // If some arguments are not provided, we already show an error.
+            return (
+                this.canBeValueOfConstantParameter(node.receiver) &&
+                getArguments(node).every((it) => this.canBeValueOfConstantParameter(it.value))
+            );
+        } else if (isSdsList(node)) {
+            return node.elements.every(this.canBeValueOfConstantParameter);
+        } else if (isSdsMap(node)) {
+            return node.entries.every(
+                (it) => this.canBeValueOfConstantParameter(it.key) && this.canBeValueOfConstantParameter(it.value),
+            );
+        } else if (isSdsMemberAccess(node)) {
+            // 1. We cannot allow all member accesses, since we might also access an attribute that has type 'Int', for
+            //    example. Thus, type checking does not always show an error, even though we already restrict the
+            //    possible types of constant parameters.
+            // 2. If the member cannot be resolved, we already show an error.
+            // 3. If the enum variant has parameters that are not provided, we already show an error.
+            const member = node.member?.target?.ref;
+            return !member || isSdsEnumVariant(member);
+        } else if (isSdsPrefixOperation(node)) {
+            return node.operator === '-' && this.canBeValueOfConstantParameter(node.operand);
+        } else if (isSdsReference(node)) {
+            // If the reference cannot be resolved, we already show an error.
+            return !node.target.ref;
+        } else {
+            return false;
+        }
+    };
 }
 
 const NO_SUBSTITUTIONS: ParameterSubstitutions = new Map();

packages/safe-ds-lang/src/language/typing/safe-ds-type-checker.ts

@@ -1,7 +1,7 @@
 import { getContainerOfType } from 'langium';
 import type { SafeDsClasses } from '../builtins/safe-ds-classes.js';
 import { isSdsEnum, type SdsAbstractResult, SdsDeclaration } from '../generated/ast.js';
-import { getParameters, Parameter } from '../helpers/nodeProperties.js';
+import { Enum, EnumVariant, getParameters, Parameter } from '../helpers/nodeProperties.js';
 import { Constant } from '../partialEvaluation/model.js';
 import { SafeDsServices } from '../safe-ds-module.js';
 import {
@@ -34,10 +34,14 @@ export class SafeDsTypeChecker {
         this.typeComputer = () => services.types.TypeComputer;
     }
 
+    // -----------------------------------------------------------------------------------------------------------------
+    // isAssignableTo
+    // -----------------------------------------------------------------------------------------------------------------
+
     /**
      * Checks whether {@link type} is assignable {@link other}.
      */
-    isAssignableTo(type: Type, other: Type): boolean {
+    isAssignableTo = (type: Type, other: Type): boolean => {
         if (type === UnknownType || other === UnknownType) {
             return false;
         } else if (other instanceof UnionType) {
@@ -63,7 +67,7 @@ export class SafeDsTypeChecker {
         } /* c8 ignore start */ else {
             throw new Error(`Unexpected type: ${type.constructor.name}`);
         } /* c8 ignore stop */
-    }
+    };
 
     private callableTypeIsAssignableTo(type: CallableType, other: Type): boolean {
         if (other instanceof ClassType) {
@@ -254,4 +258,31 @@ export class SafeDsTypeChecker {
     private unionTypeIsAssignableTo(type: UnionType, other: Type): boolean {
         return type.possibleTypes.every((it) => this.isAssignableTo(it, other));
     }
+
+    // -----------------------------------------------------------------------------------------------------------------
+    // canBeTypeOfConstantParameter
+    // -----------------------------------------------------------------------------------------------------------------
+
+    /**
+     * Checks whether {@link type} is allowed as the type of a constant parameter.
+     */
+    canBeTypeOfConstantParameter = (type: Type): boolean => {
+        if (type instanceof ClassType) {
+            return [
+                this.builtinClasses.Boolean,
+                this.builtinClasses.Float,
+                this.builtinClasses.Int,
+                this.builtinClasses.List,
+                this.builtinClasses.Map,
+                this.builtinClasses.Nothing,
+                this.builtinClasses.String,
+            ].includes(type.declaration);
+        } else if (type instanceof EnumType) {
+            return Enum.isConstant(type.declaration);
+        } else if (type instanceof EnumVariantType) {
+            return EnumVariant.isConstant(type.declaration);
+        } else {
+            return type instanceof LiteralType || type === UnknownType;
+        }
+    };
 }

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

@@ -16,7 +16,7 @@ import {
     getResults,
     Parameter,
 } from '../../../helpers/nodeProperties.js';
-import { SafeDsServices } from '../../../safe-ds-module.js';
+import type { SafeDsServices } from '../../../safe-ds-module.js';
 
 export const CODE_ANNOTATION_CALL_CONSTANT_ARGUMENT = 'annotation-call/constant-argument';
 export const CODE_ANNOTATION_CALL_MISSING_ARGUMENT_LIST = 'annotation-call/missing-argument-list';
@@ -28,10 +28,8 @@ export const annotationCallArgumentsMustBeConstant = (services: SafeDsServices)
 
     return (node: SdsAnnotationCall, accept: ValidationAcceptor) => {
         for (const argument of getArguments(node)) {
-            const evaluatedArgumentValue = partialEvaluator.evaluate(argument.value);
-
-            if (!evaluatedArgumentValue.isFullyEvaluated) {
-                accept('error', 'Arguments of annotation calls must be constant.', {
+            if (!partialEvaluator.canBeValueOfConstantParameter(argument.value)) {
+                accept('error', 'Values assigned to annotation parameters must be constant.', {
                     node: argument,
                     property: 'value',
                     code: CODE_ANNOTATION_CALL_CONSTANT_ARGUMENT,

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

@@ -1,8 +1,7 @@
 import { getContainerOfType, ValidationAcceptor } from 'langium';
 import { isSdsAnnotation, isSdsCallable, SdsParameter } from '../../../generated/ast.js';
-import { Enum, EnumVariant, Parameter } from '../../../helpers/nodeProperties.js';
+import { Parameter } from '../../../helpers/nodeProperties.js';
 import { SafeDsServices } from '../../../safe-ds-module.js';
-import { ClassType, EnumType, EnumVariantType, LiteralType, type Type, UnknownType } from '../../../typing/model.js';
 
 export const CODE_PARAMETER_CONSTANT_DEFAULT_VALUE = 'parameter/constant-default-value';
 export const CODE_PARAMETER_CONSTANT_TYPE = 'parameter/constant-type';
@@ -11,10 +10,11 @@ export const constantParameterMustHaveConstantDefaultValue = (services: SafeDsSe
     const partialEvaluator = services.evaluation.PartialEvaluator;
 
     return (node: SdsParameter, accept: ValidationAcceptor) => {
-        if (!Parameter.isConstant(node) || !node.defaultValue) return;
+        if (!Parameter.isConstant(node) || !node.defaultValue) {
+            return;
+        }
 
-        const evaluatedDefaultValue = partialEvaluator.evaluate(node.defaultValue);
-        if (!evaluatedDefaultValue.isFullyEvaluated) {
+        if (!partialEvaluator.canBeValueOfConstantParameter(node.defaultValue)) {
             const containingCallable = getContainerOfType(node, isSdsCallable);
             const kind = isSdsAnnotation(containingCallable) ? 'annotation' : 'constant';
 
@@ -28,7 +28,7 @@ export const constantParameterMustHaveConstantDefaultValue = (services: SafeDsSe
 };
 
 export const constantParameterMustHaveTypeThatCanBeEvaluatedToConstant = (services: SafeDsServices) => {
-    const isConstantType = isConstantTypeProvider(services);
+    const typeChecker = services.types.TypeChecker;
     const typeComputer = services.types.TypeComputer;
 
     return (node: SdsParameter, accept: ValidationAcceptor) => {
@@ -37,32 +37,15 @@ export const constantParameterMustHaveTypeThatCanBeEvaluatedToConstant = (servic
         }
 
         const type = typeComputer.computeType(node);
-        if (!isConstantType(type)) {
-            accept(
-                'error',
-                `The parameter must be a constant but type '${type.toString()}' cannot be evaluated to a constant.`,
-                {
-                    node,
-                    property: 'type',
-                    code: CODE_PARAMETER_CONSTANT_TYPE,
-                },
-            );
-        }
-    };
-};
-
-const isConstantTypeProvider = (services: SafeDsServices) => {
-    const builtinClasses = services.builtins.Classes;
+        if (!typeChecker.canBeTypeOfConstantParameter(type)) {
+            const containingCallable = getContainerOfType(node, isSdsCallable);
+            const kind = isSdsAnnotation(containingCallable) ? 'An annotation' : 'A constant';
 
-    return (type: Type): boolean => {
-        if (type instanceof ClassType) {
-            return builtinClasses.isBuiltinClass(type.declaration);
-        } else if (type instanceof EnumType) {
-            return Enum.isConstant(type.declaration);
-        } else if (type instanceof EnumVariantType) {
-            return EnumVariant.isConstant(type.declaration);
-        } else {
-            return type instanceof LiteralType || type === UnknownType;
+            accept('error', `${kind} parameter cannot have type '${type.toString()}'.`, {
+                node,
+                property: 'type',
+                code: CODE_PARAMETER_CONSTANT_TYPE,
+            });
         }
     };
 };

packages/safe-ds-lang/src/language/validation/other/expressions/calls.ts

@@ -1,22 +1,28 @@
 import { ValidationAcceptor } from 'langium';
-import { SdsCall } from '../../../generated/ast.js';
+import { type SdsCall } from '../../../generated/ast.js';
 import { getArguments, Parameter } from '../../../helpers/nodeProperties.js';
 import { SafeDsServices } from '../../../safe-ds-module.js';
 
 export const CODE_CALL_CONSTANT_ARGUMENT = 'call/constant-argument';
 
-export const callArgumentsMustBeConstantIfParameterIsConstant = (services: SafeDsServices) => {
+export const callArgumentMustBeConstantIfParameterIsConstant = (services: SafeDsServices) => {
     const nodeMapper = services.helpers.NodeMapper;
     const partialEvaluator = services.evaluation.PartialEvaluator;
 
     return (node: SdsCall, accept: ValidationAcceptor) => {
         for (const argument of getArguments(node)) {
+            if (!argument.value) {
+                /* c8 ignore next 2 */
+                return;
+            }
+
             const parameter = nodeMapper.argumentToParameter(argument);
-            if (!Parameter.isConstant(parameter)) continue;
+            if (!Parameter.isConstant(parameter)) {
+                return;
+            }
 
-            const evaluatedArgumentValue = partialEvaluator.evaluate(argument.value);
-            if (!evaluatedArgumentValue.isFullyEvaluated) {
-                accept('error', 'Arguments assigned to constant parameters must be constant.', {
+            if (!partialEvaluator.canBeValueOfConstantParameter(argument.value)) {
+                accept('error', 'Values assigned to constant parameters must be constant.', {
                     node: argument,
                     property: 'value',
                     code: CODE_CALL_CONSTANT_ARGUMENT,

packages/safe-ds-lang/src/language/validation/safe-ds-validator.ts

@@ -86,7 +86,7 @@ import {
     typeParameterMustHaveSufficientContext,
     typeParameterMustNotBeUsedInNestedNamedTypeDeclarations,
 } from './other/declarations/typeParameters.js';
-import { callArgumentsMustBeConstantIfParameterIsConstant } from './other/expressions/calls.js';
+import { callArgumentMustBeConstantIfParameterIsConstant } from './other/expressions/calls.js';
 import { divisionDivisorMustNotBeZero } from './other/expressions/infixOperations.js';
 import {
     lambdaMustBeAssignedToTypedParameter,
@@ -223,7 +223,7 @@ export const registerValidationChecks = function (services: SafeDsServices) {
         SdsBlockLambda: [blockLambdaMustContainUniqueNames],
         SdsCall: [
             callArgumentListShouldBeNeeded(services),
-            callArgumentsMustBeConstantIfParameterIsConstant(services),
+            callArgumentMustBeConstantIfParameterIsConstant(services),
             callReceiverMustBeCallable(services),
         ],
         SdsCallableType: [