feat: error if call leads to infinite recursion (#783)

Closes #667

### Summary of Changes

Show an error if a call leads to infinite recursion.

Author: lars-reimann

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

@@ -4,6 +4,7 @@ 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 CODE_CALL_INFINITE_RECURSION = 'call/infinite-recursion';
 
 export const callArgumentMustBeConstantIfParameterIsConstant = (services: SafeDsServices) => {
     const nodeMapper = services.helpers.NodeMapper;
@@ -31,3 +32,16 @@ export const callArgumentMustBeConstantIfParameterIsConstant = (services: SafeDs
         }
     };
 };
+
+export const callMustNotBeRecursive = (services: SafeDsServices) => {
+    const callGraphComputer = services.flow.CallGraphComputer;
+
+    return (node: SdsCall, accept: ValidationAcceptor) => {
+        if (callGraphComputer.isRecursive(node)) {
+            accept('error', 'Call leads to infinite recursion.', {
+                node,
+                code: CODE_CALL_INFINITE_RECURSION,
+            });
+        }
+    };
+};

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

@@ -86,7 +86,7 @@ import {
     typeParameterMustHaveSufficientContext,
     typeParameterMustNotBeUsedInNestedNamedTypeDeclarations,
 } from './other/declarations/typeParameters.js';
-import { callArgumentMustBeConstantIfParameterIsConstant } from './other/expressions/calls.js';
+import { callArgumentMustBeConstantIfParameterIsConstant, callMustNotBeRecursive } from './other/expressions/calls.js';
 import { divisionDivisorMustNotBeZero } from './other/expressions/infixOperations.js';
 import {
     lambdaMustBeAssignedToTypedParameter,
@@ -223,6 +223,7 @@ export const registerValidationChecks = function (services: SafeDsServices) {
         SdsCall: [
             callArgumentListShouldBeNeeded(services),
             callArgumentMustBeConstantIfParameterIsConstant(services),
+            callMustNotBeRecursive(services),
             callReceiverMustBeCallable(services),
         ],
         SdsCallableType: [

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

@@ -1,12 +1,6 @@
 import { describe, expect, it } from 'vitest';
 import { EmptyFileSystem, isNamed } from 'langium';
-import {
-    isSdsBlockLambda,
-    isSdsCall,
-    isSdsExpressionLambda,
-    isSdsModule,
-    SdsCall,
-} from '../../../src/language/generated/ast.js';
+import { isSdsBlockLambda, isSdsExpressionLambda, isSdsModule, SdsCall } from '../../../src/language/generated/ast.js';
 import { createSafeDsServices } from '../../../src/language/index.js';
 import { createCallGraphTests } from './creator.js';
 import { getNodeOfType } from '../../helpers/nodeFinder.js';
@@ -18,40 +12,6 @@ const services = createSafeDsServices(EmptyFileSystem).SafeDs;
 const callGraphComputer = services.flow.CallGraphComputer;
 
 describe('SafeDsCallGraphComputer', () => {
-    describe('isRecursive', () => {
-        it('should return true for recursive calls', async () => {
-            const call = await getNodeOfType(
-                services,
-                `
-                    segment a() {
-                        b();
-                    }
-
-                    segment b() {
-                        a();
-                    }
-                `,
-                isSdsCall,
-            );
-            expect(callGraphComputer.isRecursive(call)).toBeTruthy();
-        });
-
-        it('should return false for non-recursive calls', async () => {
-            const call = await getNodeOfType(
-                services,
-                `
-                    segment a() {
-                        b();
-                    }
-
-                    segment b() {}
-                `,
-                isSdsCall,
-            );
-            expect(callGraphComputer.isRecursive(call)).toBeFalsy();
-        });
-    });
-
     describe('getCallGraph', async () => {
         it.each(await createCallGraphTests())('$testName', async (test) => {
             // Test is invalid

packages/safe-ds-lang/tests/resources/validation/other/expressions/calls/recursion/direct.sdstest

@@ -0,0 +1,16 @@
+package tests.validation.other.expression.calls.recurcion.direct
+
+segment s1() {
+    // $TEST$ error "Call leads to infinite recursion."
+    »s2()«;
+}
+
+segment s2() {
+    // $TEST$ error "Call leads to infinite recursion."
+    »s3()«;
+}
+
+segment s3() {
+    // $TEST$ error "Call leads to infinite recursion."
+    »s2()«;
+}

packages/safe-ds-lang/tests/resources/validation/other/expressions/calls/recursion/not recursive.sdstest

@@ -0,0 +1,15 @@
+package tests.validation.other.expression.calls.recurcion.notRecursive
+
+/**
+ * Even though "s2" gets called twice, this does not lead to infinite recursion, since the 2nd time the default, empty
+ * lambda is used for "f".
+ */
+
+segment s1() {
+    // $TEST$ no error "Call leads to infinite recursion."
+    »s2(() -> s2())«;
+}
+
+segment s2(f: () -> () = () {}) {
+    f();
+}

packages/safe-ds-lang/tests/resources/validation/other/expressions/calls/recursion/transitive via function pointer argument.sdstest

@@ -0,0 +1,10 @@
+package tests.validation.other.expression.calls.recurcion.transitiveViaFunctionPointerArgument
+
+segment s1() {
+    // $TEST$ error "Call leads to infinite recursion."
+    »s2(s1)«;
+}
+
+segment s2(f: () -> ()) {
+    f();
+}

packages/safe-ds-lang/tests/resources/validation/other/expressions/calls/recursion/transitive via lambda argument.sdstest

@@ -0,0 +1,10 @@
+package tests.validation.other.expression.calls.recurcion.transitiveViaLambdaArgument
+
+segment s1() {
+    // $TEST$ error "Call leads to infinite recursion."
+    »s2(() -> s1())«;
+}
+
+segment s2(f: () -> ()) {
+    f();
+}

packages/safe-ds-lang/tests/resources/validation/other/expressions/calls/recursion/transitive.sdstest

@@ -0,0 +1,16 @@
+package tests.validation.other.expression.calls.recurcion.transitive
+
+segment s1() {
+    // $TEST$ error "Call leads to infinite recursion."
+    »s2()«;
+}
+
+segment s2() {
+    // $TEST$ error "Call leads to infinite recursion."
+    »s3()«;
+}
+
+segment s3() {
+    // $TEST$ error "Call leads to infinite recursion."
+    »s1()«;
+}