feat: streamline purity information (#779)

### Summary of Changes

Remove the option to mark callable parameters as `@Pure`, since it could
collide with the impurity reasons on the containing function in various
ways. Now only the context decides, whether a callable parameter only
accepts pure callables or may be potentially impure.

packages/safe-ds-lang/src/language/builtins/safe-ds-annotations.ts

@@ -85,7 +85,7 @@ export class SafeDsAnnotations extends SafeDsModuleMembers<SdsAnnotation> {
         return this.getAnnotation(PURITY_URI, 'Impure');
     }
 
-    callsPure(node: SdsFunction | SdsParameter | undefined): boolean {
+    callsPure(node: SdsFunction | undefined): boolean {
         return hasAnnotationCallOf(node, this.Pure);
     }
 

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

@@ -1,8 +1,8 @@
 import { stream, type ValidationAcceptor } from 'langium';
 import { isSubset } from '../../helpers/collectionUtils.js';
-import { isSdsCall, isSdsFunction, isSdsList, type SdsFunction, type SdsParameter } from '../generated/ast.js';
+import { isSdsCall, isSdsFunction, isSdsList, type SdsFunction } from '../generated/ast.js';
 import { findFirstAnnotationCallOf, getArguments, getParameters } from '../helpers/nodeProperties.js';
-import { EvaluatedEnumVariant, StringConstant } from '../partialEvaluation/model.js';
+import { StringConstant } from '../partialEvaluation/model.js';
 import type { SafeDsServices } from '../safe-ds-module.js';
 import { CallableType } from '../typing/model.js';
 
@@ -12,66 +12,6 @@ export const CODE_PURITY_IMPURITY_REASONS_OF_OVERRIDING_METHOD = 'purity/impurit
 export const CODE_PURITY_INVALID_PARAMETER_NAME = 'purity/invalid-parameter-name';
 export const CODE_PURITY_MUST_BE_SPECIFIED = 'purity/must-be-specified';
 export const CODE_PURITY_POTENTIALLY_IMPURE_PARAMETER_NOT_CALLABLE = 'purity/potentially-impure-parameter-not-callable';
-export const CODE_PURITY_PURE_PARAMETER_MUST_HAVE_CALLABLE_TYPE = 'purity/pure-parameter-must-have-callable-type';
-
-export const callableParameterPurityMustBeSpecified = (services: SafeDsServices) => {
-    const builtinAnnotations = services.builtins.Annotations;
-    const possibleImpurityReasons = services.builtins.ImpurityReasons;
-    const typeComputer = services.types.TypeComputer;
-
-    return (node: SdsFunction, accept: ValidationAcceptor) => {
-        const potentiallyImpureParameterCall = possibleImpurityReasons.PotentiallyImpureParameterCall;
-        if (!potentiallyImpureParameterCall) {
-            return;
-        }
-
-        const parameterNameParameter = getParameters(potentiallyImpureParameterCall).find(
-            (it) => it.name === 'parameterName',
-        )!;
-        const impurityReasons = builtinAnnotations.streamImpurityReasons(node).toArray();
-
-        for (const parameter of getParameters(node)) {
-            const parameterType = typeComputer.computeType(parameter);
-            if (!(parameterType instanceof CallableType)) {
-                continue;
-            }
-
-            const expectedImpurityReason = new EvaluatedEnumVariant(
-                possibleImpurityReasons.PotentiallyImpureParameterCall,
-                new Map([[parameterNameParameter, new StringConstant(parameter.name)]]),
-            );
-
-            if (
-                builtinAnnotations.callsPure(parameter) &&
-                impurityReasons.some((it) => it.equals(expectedImpurityReason))
-            ) {
-                accept(
-                    'error',
-                    "'@Pure' and the impurity reason 'PotentiallyImpureParameterCall' on the containing function are mutually exclusive.",
-                    {
-                        node: parameter,
-                        property: 'name',
-                        code: CODE_PURITY_IMPURE_AND_PURE,
-                    },
-                );
-            } else if (
-                !builtinAnnotations.callsPure(node) &&
-                !builtinAnnotations.callsPure(parameter) &&
-                !impurityReasons.some((it) => it.equals(expectedImpurityReason))
-            ) {
-                accept(
-                    'error',
-                    "The purity of a callable parameter must be specified. Call the annotation '@Pure' or add the impurity reason 'PotentiallyImpureParameterCall' to the containing function.",
-                    {
-                        node: parameter,
-                        property: 'name',
-                        code: CODE_PURITY_MUST_BE_SPECIFIED,
-                    },
-                );
-            }
-        }
-    };
-};
 
 export const functionPurityMustBeSpecified = (services: SafeDsServices) => {
     const annotations = services.builtins.Annotations;
@@ -275,24 +215,3 @@ export const impurityReasonShouldNotBeSetMultipleTimes = (services: SafeDsServic
         }
     };
 };
-
-export const pureParameterMustHaveCallableType = (services: SafeDsServices) => {
-    const builtinAnnotations = services.builtins.Annotations;
-    const typeComputer = services.types.TypeComputer;
-
-    return (node: SdsParameter, accept: ValidationAcceptor) => {
-        // Don't show an error if no type is specified (yet) or if the parameter is not marked as pure
-        if (!node.type || !builtinAnnotations.callsPure(node)) {
-            return;
-        }
-
-        const type = typeComputer.computeType(node);
-        if (!(type instanceof CallableType)) {
-            accept('error', 'A pure parameter must have a callable type.', {
-                node,
-                property: 'name',
-                code: CODE_PURITY_PURE_PARAMETER_MUST_HAVE_CALLABLE_TYPE,
-            });
-        }
-    };
-};

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

@@ -135,12 +135,10 @@ import {
     unionTypeShouldNotHaveDuplicateTypes,
 } from './other/types/unionTypes.js';
 import {
-    callableParameterPurityMustBeSpecified,
     functionPurityMustBeSpecified,
     impurityReasonParameterNameMustBelongToParameterOfCorrectType,
     impurityReasonShouldNotBeSetMultipleTimes,
     impurityReasonsOfOverridingMethodMustBeSubsetOfOverriddenMethod,
-    pureParameterMustHaveCallableType,
 } from './purity.js';
 import {
     annotationCallArgumentListShouldBeNeeded,
@@ -157,7 +155,6 @@ import {
     importedDeclarationAliasShouldDifferFromDeclarationName,
     memberAccessNullSafetyShouldBeNeeded,
     namedTypeTypeArgumentListShouldBeNeeded,
-    pureAnnotationCallOnParameterShouldBeNeeded,
     segmentResultListShouldNotBeEmpty,
     typeParameterListShouldNotBeEmpty,
     unionTypeShouldNotHaveASingularTypeArgument,
@@ -256,14 +253,12 @@ export const registerValidationChecks = function (services: SafeDsServices) {
         SdsEnumVariant: [enumVariantMustContainUniqueNames, enumVariantParameterListShouldNotBeEmpty],
         SdsExpressionLambda: [expressionLambdaMustContainUniqueNames],
         SdsFunction: [
-            callableParameterPurityMustBeSpecified(services),
             functionMustContainUniqueNames,
             functionResultListShouldNotBeEmpty,
             functionPurityMustBeSpecified(services),
             impurityReasonsOfOverridingMethodMustBeSubsetOfOverriddenMethod(services),
             impurityReasonParameterNameMustBelongToParameterOfCorrectType(services),
             impurityReasonShouldNotBeSetMultipleTimes(services),
-            pureAnnotationCallOnParameterShouldBeNeeded(services),
             pythonCallMustOnlyContainValidTemplateExpressions(services),
             pythonNameMustNotBeSetIfPythonCallIsSet(services),
         ],
@@ -320,7 +315,6 @@ export const registerValidationChecks = function (services: SafeDsServices) {
             constantParameterMustHaveTypeThatCanBeEvaluatedToConstant(services),
             parameterMustHaveTypeHint,
             parameterDefaultValueTypeMustMatchParameterType(services),
-            pureParameterMustHaveCallableType(services),
             requiredParameterMustNotBeDeprecated(services),
             requiredParameterMustNotBeExpert(services),
         ],

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

@@ -20,10 +20,10 @@ import {
     SdsTypeParameterList,
     SdsUnionType,
 } from '../generated/ast.js';
-import { findFirstAnnotationCallOf, getParameters, getTypeParameters, Parameter } from '../helpers/nodeProperties.js';
+import { getParameters, getTypeParameters, Parameter } from '../helpers/nodeProperties.js';
 import { NullConstant } from '../partialEvaluation/model.js';
 import { SafeDsServices } from '../safe-ds-module.js';
-import { CallableType, UnknownType } from '../typing/model.js';
+import { UnknownType } from '../typing/model.js';
 
 export const CODE_STYLE_UNNECESSARY_ASSIGNMENT = 'style/unnecessary-assignment';
 export const CODE_STYLE_UNNECESSARY_ARGUMENT_LIST = 'style/unnecessary-argument-list';
@@ -33,7 +33,6 @@ export const CODE_STYLE_UNNECESSARY_CONSTRAINT_LIST = 'style/unnecessary-constra
 export const CODE_STYLE_UNNECESSARY_ELVIS_OPERATOR = 'style/unnecessary-elvis-operator';
 export const CODE_STYLE_UNNECESSARY_IMPORT_ALIAS = 'style/unnecessary-import-alias';
 export const CODE_STYLE_UNNECESSARY_PARAMETER_LIST = 'style/unnecessary-parameter-list';
-export const CODE_STYLE_UNNECESSARY_PURE_ANNOTATION_CALL = 'style/unnecessary-pure-annotation-call';
 export const CODE_STYLE_UNNECESSARY_RESULT_LIST = 'style/unnecessary-result-list';
 export const CODE_STYLE_UNNECESSARY_SAFE_ACCESS = 'style/unnecessary-safe-access';
 export const CODE_STYLE_UNNECESSARY_TYPE_ARGUMENT_LIST = 'style/unnecessary-type-argument-list';
@@ -252,40 +251,6 @@ export const enumVariantParameterListShouldNotBeEmpty = (node: SdsEnumVariant, a
     }
 };
 
-// -----------------------------------------------------------------------------
-// Unnecessary pure annotation calls
-// -----------------------------------------------------------------------------
-
-export const pureAnnotationCallOnParameterShouldBeNeeded = (services: SafeDsServices) => {
-    const builtinAnnotations = services.builtins.Annotations;
-    const typeComputer = services.types.TypeComputer;
-
-    return (node: SdsFunction, accept: ValidationAcceptor) => {
-        if (!builtinAnnotations.callsPure(node) || builtinAnnotations.callsImpure(node)) {
-            return;
-        }
-
-        for (const parameter of getParameters(node)) {
-            const parameterType = typeComputer.computeType(parameter);
-            if (!(parameterType instanceof CallableType)) {
-                continue;
-            }
-
-            const pureAnnotationCall = findFirstAnnotationCallOf(parameter, builtinAnnotations.Pure);
-            if (pureAnnotationCall) {
-                accept(
-                    'info',
-                    'Callable parameters of a pure function are always pure, so this annotation call can be removed.',
-                    {
-                        node: pureAnnotationCall,
-                        code: CODE_STYLE_UNNECESSARY_PURE_ANNOTATION_CALL,
-                    },
-                );
-            }
-        }
-    };
-};
-
 // -----------------------------------------------------------------------------
 // Unnecessary result lists
 // -----------------------------------------------------------------------------

packages/safe-ds-lang/src/resources/builtins/safeds/lang/purity.sdsstub

@@ -1,25 +1,21 @@
 package safeds.lang
 
 /**
- * **If called on a function:** Indicates that the function has no side effects and always returns the same results
- * given the same arguments.
+ * Indicates that the function has no side effects and always returns the same results given the same arguments.
  *
  * Calls to such a function may be eliminated, if its results are not used. Moreover, the function can be memoized, i.e.
  * we can remember its results for a set of arguments. Finally, a pure function can be called at any time, allowing
  * reordering of calls or parallelization.
- *
- * **If called on a parameter:** Indicates that the parameter only accepts pure callables.
  */
 @Experimental
-@Target([AnnotationTarget.Function, AnnotationTarget.Parameter])
+@Target([AnnotationTarget.Function])
 annotation Pure
 
 /**
  * Indicates that the function has side effects and/or does not always return the same results given the same arguments.
  *
  * @param allReasons
- *     A list of **all** reasons why the function is impure. If no specific {@link ImpurityReason} applies, include
- *     `ImpurityReason.Other`.
+ *     A list of **all** reasons why the function is impure. If no specific {@link ImpurityReason} applies, include `ImpurityReason.Other`.
  */
 @Experimental
 @Target([AnnotationTarget.Function])