feat: add endless recursion as an impurity reason (#788)

### Summary of Changes

Endless recursion is now included in the inferred impurity reasons of an
expression/callable.

Author: lars-reimann

packages/safe-ds-lang/src/language/flow/safe-ds-call-graph-computer.ts

@@ -124,11 +124,13 @@ export class SafeDsCallGraphComputer {
             const call = this.createSyntheticCallForCall(node, substitutions);
             return this.getCallGraphWithRecursionCheck(call, []);
         } else {
+            const children = this.getExecutedCallsInCallable(node, substitutions).map((it) => {
+                return this.getCallGraphWithRecursionCheck(it, []);
+            });
             return new CallGraph(
                 node,
-                this.getExecutedCallsInCallable(node, substitutions).map((it) => {
-                    return this.getCallGraphWithRecursionCheck(it, []);
-                }),
+                children,
+                children.some((it) => it.isRecursive),
             );
         }
     }

packages/safe-ds-lang/src/language/generation/safe-ds-python-generator.ts

@@ -359,7 +359,7 @@ export class SafeDsPythonGenerator {
     }
 
     private generateBlock(block: SdsBlock, frame: GenerationInfoFrame): CompositeGeneratorNode {
-        let statements = getStatements(block).filter((stmt) => this.hasStatementEffect(stmt));
+        let statements = getStatements(block).filter((stmt) => this.purityComputer.statementDoesSomething(stmt));
         if (statements.length === 0) {
             return traceToNode(block)('pass');
         }
@@ -368,21 +368,6 @@ export class SafeDsPythonGenerator {
         })!;
     }
 
-    private hasStatementEffect(statement: SdsStatement): boolean {
-        if (isSdsAssignment(statement)) {
-            const assignees = getAssignees(statement);
-            return (
-                assignees.some((value) => !isSdsWildcard(value)) ||
-                (statement.expression !== undefined &&
-                    this.purityComputer.expressionHasSideEffects(statement.expression))
-            );
-        } else if (isSdsExpressionStatement(statement)) {
-            return this.purityComputer.expressionHasSideEffects(statement.expression);
-        }
-        /* c8 ignore next */
-        return false;
-    }
-
     private generateStatement(statement: SdsStatement, frame: GenerationInfoFrame): CompositeGeneratorNode {
         if (isSdsAssignment(statement)) {
             return traceToNode(statement)(this.generateAssignment(statement, frame));

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

@@ -100,6 +100,23 @@ export class PotentiallyImpureParameterCall extends ImpurityReason {
     }
 }
 
+/**
+ * A function contains a call that leads to endless recursion.
+ */
+class EndlessRecursionClass extends ImpurityReason {
+    override isSideEffect = true;
+
+    override equals(other: unknown): boolean {
+        return other instanceof EndlessRecursionClass;
+    }
+
+    override toString(): string {
+        return 'Endless recursion';
+    }
+}
+
+export const EndlessRecursion = new EndlessRecursionClass();
+
 /**
  * A function is impure due to some reason that is not covered by the other impurity reasons.
  */

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

@@ -11,25 +11,30 @@ import { isEmpty } from '../../helpers/collectionUtils.js';
 import type { SafeDsCallGraphComputer } from '../flow/safe-ds-call-graph-computer.js';
 import type { SafeDsServices } from '../safe-ds-module.js';
 import {
+    EndlessRecursion,
     FileRead,
     FileWrite,
     type ImpurityReason,
     OtherImpurityReason,
     PotentiallyImpureParameterCall,
 } from './model.js';
 import {
+    isSdsAssignment,
+    isSdsExpressionStatement,
     isSdsFunction,
     isSdsLambda,
+    isSdsWildcard,
     SdsCall,
     SdsCallable,
     SdsExpression,
     SdsFunction,
     SdsParameter,
+    SdsStatement,
 } from '../generated/ast.js';
 import { EvaluatedEnumVariant, ParameterSubstitutions, StringConstant } from '../partialEvaluation/model.js';
 import { SafeDsAnnotations } from '../builtins/safe-ds-annotations.js';
 import { SafeDsImpurityReasons } from '../builtins/safe-ds-enums.js';
-import { getParameters } from '../helpers/nodeProperties.js';
+import { getAssignees, getParameters } from '../helpers/nodeProperties.js';
 import { isContainedInOrEqual } from '../helpers/astUtils.js';
 
 export class SafeDsPurityComputer {
@@ -63,7 +68,7 @@ export class SafeDsPurityComputer {
      * The parameter substitutions to use. These are **not** the argument of a call, but the values of the parameters
      * of any containing callables, i.e. the context of the node.
      */
-    isPureCallable(node: SdsCallable, substitutions = NO_SUBSTITUTIONS): boolean {
+    isPureCallable(node: SdsCallable | undefined, substitutions = NO_SUBSTITUTIONS): boolean {
         return isEmpty(this.getImpurityReasonsForCallable(node, substitutions));
     }
 
@@ -77,7 +82,7 @@ export class SafeDsPurityComputer {
      * The parameter substitutions to use. These are **not** the argument of a call, but the values of the parameters
      * of any containing callables, i.e. the context of the node.
      */
-    isPureExpression(node: SdsExpression, substitutions = NO_SUBSTITUTIONS): boolean {
+    isPureExpression(node: SdsExpression | undefined, substitutions = NO_SUBSTITUTIONS): boolean {
         return isEmpty(this.getImpurityReasonsForExpression(node, substitutions));
     }
 
@@ -91,7 +96,7 @@ export class SafeDsPurityComputer {
      * The parameter substitutions to use. These are **not** the argument of a call, but the values of the parameters
      * of any containing callables, i.e. the context of the node.
      */
-    callableHasSideEffects(node: SdsCallable, substitutions = NO_SUBSTITUTIONS): boolean {
+    callableHasSideEffects(node: SdsCallable | undefined, substitutions = NO_SUBSTITUTIONS): boolean {
         return this.getImpurityReasonsForCallable(node, substitutions).some((it) => it.isSideEffect);
     }
 
@@ -105,10 +110,37 @@ export class SafeDsPurityComputer {
      * The parameter substitutions to use. These are **not** the argument of a call, but the values of the parameters
      * of any containing callables, i.e. the context of the node.
      */
-    expressionHasSideEffects(node: SdsExpression, substitutions = NO_SUBSTITUTIONS): boolean {
+    expressionHasSideEffects(node: SdsExpression | undefined, substitutions = NO_SUBSTITUTIONS): boolean {
         return this.getImpurityReasonsForExpression(node, substitutions).some((it) => it.isSideEffect);
     }
 
+    /**
+     * Returns whether the given statement does something. It must either
+     *     - create a placeholder,
+     *     - assign to a result, or
+     *     - call a function that has side effects.
+     *
+     * @param node
+     * The statement to check.
+     *
+     * @param substitutions
+     * The parameter substitutions to use. These are **not** the argument of a call, but the values of the parameters
+     * of any containing callables, i.e. the context of the node.
+     */
+    statementDoesSomething(node: SdsStatement, substitutions = NO_SUBSTITUTIONS): boolean {
+        if (isSdsAssignment(node)) {
+            return (
+                !getAssignees(node).every(isSdsWildcard) ||
+                this.expressionHasSideEffects(node.expression, substitutions)
+            );
+        } else if (isSdsExpressionStatement(node)) {
+            return this.expressionHasSideEffects(node.expression, substitutions);
+        } else {
+            /* c8 ignore next 2 */
+            return false;
+        }
+    }
+
     /**
      * Returns the reasons why the given callable is impure.
      *
@@ -119,7 +151,7 @@ export class SafeDsPurityComputer {
      * The parameter substitutions to use. These are **not** the argument of a call, but the values of the parameters
      * of any containing callables, i.e. the context of the node.
      */
-    getImpurityReasonsForCallable(node: SdsCallable, substitutions = NO_SUBSTITUTIONS): ImpurityReason[] {
+    getImpurityReasonsForCallable(node: SdsCallable | undefined, substitutions = NO_SUBSTITUTIONS): ImpurityReason[] {
         return this.getImpurityReasons(node, substitutions);
     }
 
@@ -133,28 +165,54 @@ export class SafeDsPurityComputer {
      * The parameter substitutions to use. These are **not** the argument of a call, but the values of the parameters
      * of any containing callables, i.e. the context of the node.
      */
-    getImpurityReasonsForExpression(node: SdsExpression, substitutions = NO_SUBSTITUTIONS): ImpurityReason[] {
+    getImpurityReasonsForExpression(
+        node: SdsExpression | undefined,
+        substitutions = NO_SUBSTITUTIONS,
+    ): ImpurityReason[] {
         return this.getExecutedCallsInExpression(node).flatMap((it) => this.getImpurityReasons(it, substitutions));
     }
 
-    private getImpurityReasons(node: SdsCall | SdsCallable, substitutions = NO_SUBSTITUTIONS): ImpurityReason[] {
-        const key = this.getNodeId(node);
-        return this.reasonsCache.get(key, () => {
-            return this.callGraphComputer
-                .getCallGraph(node, substitutions)
-                .streamCalledCallables()
-                .flatMap((it) => {
-                    if (isSdsFunction(it)) {
-                        return this.getImpurityReasonsForFunction(it);
-                    } else {
-                        return EMPTY_STREAM;
-                    }
-                })
-                .toArray();
+    private getImpurityReasons(
+        node: SdsCall | SdsCallable | undefined,
+        substitutions = NO_SUBSTITUTIONS,
+    ): ImpurityReason[] {
+        if (!node) {
+            /* c8 ignore next 2 */
+            return [];
+        }
+
+        // Cache the result if no substitutions are given
+        if (isEmpty(substitutions)) {
+            const key = this.getNodeId(node);
+            return this.reasonsCache.get(key, () => {
+                return this.doGetImpurityReasons(node, substitutions);
+            });
+        } else {
+            /* c8 ignore next 2 */
+            return this.doGetImpurityReasons(node, substitutions);
+        }
+    }
+
+    private doGetImpurityReasons(node: SdsCall | SdsCallable, substitutions = NO_SUBSTITUTIONS): ImpurityReason[] {
+        const callGraph = this.callGraphComputer.getCallGraph(node, substitutions);
+
+        const recursionImpurityReason: ImpurityReason[] = [];
+        if (callGraph.isRecursive) {
+            recursionImpurityReason.push(EndlessRecursion);
+        }
+
+        const otherImpurityReasons = callGraph.streamCalledCallables().flatMap((it) => {
+            if (isSdsFunction(it)) {
+                return this.getImpurityReasonsForFunction(it);
+            } else {
+                return EMPTY_STREAM;
+            }
         });
+
+        return [...recursionImpurityReason, ...otherImpurityReasons];
     }
 
-    private getExecutedCallsInExpression(expression: SdsExpression): SdsCall[] {
+    private getExecutedCallsInExpression(expression: SdsExpression | undefined): SdsCall[] {
         return this.callGraphComputer.getAllContainedCalls(expression).filter((it) => {
             // Keep only calls that are not contained in a lambda inside the expression
             const containingLambda = getContainerOfType(it, isSdsLambda);

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

@@ -1,57 +1,18 @@
-import {
-    isSdsAssignment,
-    isSdsExpressionStatement,
-    isSdsWildcard,
-    SdsExpression,
-    SdsStatement,
-} from '../../../generated/ast.js';
+import { SdsStatement } from '../../../generated/ast.js';
 import { ValidationAcceptor } from 'langium';
 import { SafeDsServices } from '../../../safe-ds-module.js';
-import { getAssignees } from '../../../helpers/nodeProperties.js';
 
 export const CODE_STATEMENT_HAS_NO_EFFECT = 'statement/has-no-effect';
 
 export const statementMustDoSomething = (services: SafeDsServices) => {
-    const statementDoesSomething = statementDoesSomethingProvider(services);
+    const purityComputer = services.purity.PurityComputer;
 
     return (node: SdsStatement, accept: ValidationAcceptor): void => {
-        if (!statementDoesSomething(node)) {
+        if (!purityComputer.statementDoesSomething(node)) {
             accept('warning', 'This statement does nothing.', {
                 node,
                 code: CODE_STATEMENT_HAS_NO_EFFECT,
             });
         }
     };
 };
-
-const statementDoesSomethingProvider = (services: SafeDsServices) => {
-    const statementExpressionDoesSomething = statementExpressionDoesSomethingProvider(services);
-
-    return (node: SdsStatement): boolean => {
-        if (isSdsAssignment(node)) {
-            return !getAssignees(node).every(isSdsWildcard) || statementExpressionDoesSomething(node.expression);
-        } else if (isSdsExpressionStatement(node)) {
-            return statementExpressionDoesSomething(node.expression);
-        } else {
-            /* c8 ignore next 2 */
-            return false;
-        }
-    };
-};
-
-const statementExpressionDoesSomethingProvider = (services: SafeDsServices) => {
-    const callGraphComputer = services.flow.CallGraphComputer;
-    const purityComputer = services.purity.PurityComputer;
-
-    return (node: SdsExpression | undefined): boolean => {
-        if (!node) {
-            /* c8 ignore next 2 */
-            return false;
-        }
-
-        return (
-            callGraphComputer.getAllContainedCalls(node).some((it) => callGraphComputer.isRecursive(it)) ||
-            !purityComputer.isPureExpression(node)
-        );
-    };
-};

packages/safe-ds-lang/tests/language/documentation/safe-ds-comment-provider.test.ts

@@ -1,7 +1,6 @@
 import { AssertionError } from 'assert';
 import { AstNode, EmptyFileSystem } from 'langium';
-import { clearDocuments } from 'langium/test';
-import { afterEach, describe, expect, it } from 'vitest';
+import { describe, expect, it } from 'vitest';
 import {
     isSdsAnnotation,
     isSdsAttribute,
@@ -21,10 +20,6 @@ const commentProvider = services.documentation.CommentProvider;
 const testComment = '/* test */';
 
 describe('SafeDsCommentProvider', () => {
-    afterEach(async () => {
-        await clearDocuments(services);
-    });
-
     const testCases: CommentProviderTest[] = [
         {
             testName: 'commented module member (without annotations)',

packages/safe-ds-lang/tests/language/documentation/safe-ds-documentation-provider.test.ts

@@ -1,6 +1,5 @@
 import { AstNode, EmptyFileSystem, expandToString } from 'langium';
-import { clearDocuments } from 'langium/test';
-import { afterEach, describe, expect, it } from 'vitest';
+import { describe, expect, it } from 'vitest';
 import { normalizeLineBreaks } from '../../../src/helpers/stringUtils.js';
 import {
     isSdsAnnotation,
@@ -17,10 +16,6 @@ const documentationProvider = services.documentation.DocumentationProvider;
 const testDocumentation = 'Lorem ipsum.';
 
 describe('SafeDsDocumentationProvider', () => {
-    afterEach(async () => {
-        await clearDocuments(services);
-    });
-
     const testCases: DocumentationProviderTest[] = [
         {
             testName: 'module member',

packages/safe-ds-lang/tests/language/generation/safe-ds-python-generator.test.ts

@@ -1,25 +1,15 @@
-import { createSafeDsServices } from '../../../src/language/index.js';
-import { clearDocuments } from 'langium/test';
-import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+import { createSafeDsServicesWithBuiltins } from '../../../src/language/index.js';
+import { describe, expect, it } from 'vitest';
 import { NodeFileSystem } from 'langium/node';
 import { createGenerationTests } from './creator.js';
 import { loadDocuments } from '../../helpers/testResources.js';
 import { stream } from 'langium';
 
-const services = createSafeDsServices(NodeFileSystem).SafeDs;
+const services = (await createSafeDsServicesWithBuiltins(NodeFileSystem)).SafeDs;
 const pythonGenerator = services.generation.PythonGenerator;
 const generationTests = createGenerationTests();
 
 describe('generation', async () => {
-    beforeEach(async () => {
-        // Load the builtin library
-        await services.shared.workspace.WorkspaceManager.initializeWorkspace([]);
-    });
-
-    afterEach(async () => {
-        await clearDocuments(services);
-    });
-
     it.each(await generationTests)('$testName', async (test) => {
         // Test is invalid
         if (test.error) {

packages/safe-ds-lang/tests/language/grammar/safe-ds-grammar.test.ts

@@ -1,18 +1,13 @@
-import { afterEach, describe, it } from 'vitest';
+import { describe, it } from 'vitest';
 import { createSafeDsServices } from '../../../src/language/index.js';
 import { AssertionError } from 'assert';
 import { NodeFileSystem } from 'langium/node';
 import { createGrammarTests } from './creator.js';
-import { clearDocuments } from 'langium/test';
 import { getSyntaxErrors } from '../../helpers/diagnostics.js';
 
 const services = createSafeDsServices(NodeFileSystem).SafeDs;
 
 describe('grammar', () => {
-    afterEach(async () => {
-        await clearDocuments(services);
-    });
-
     it.each(createGrammarTests())('$testName', async (test) => {
         // Test is invalid
         if (test.error) {