fix: type inference for lambdas and their parameters

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

@@ -125,11 +125,11 @@ export class SafeDsTypeComputer {
     private readonly typeChecker: SafeDsTypeChecker;
 
     /**
-     * Contains all lambda parameters that are currently being computed. When computing the types of lambda parameters,
-     * they must only access the type of the containing lambda, if they are not contained in this set themselves.
-     * Otherwise, this would cause endless recursion.
+     * Contains all calls for which we currently compute substitutions. This prevents endless recursion, since the
+     * substitutions of a call depend on the inferred types of their arguments, which may be lambdas. The inferred type
+     * of a lambda in turn depends on the substitutions of the call it is passed to.
      */
-    private readonly incompleteLambdaParameters = new Set<SdsParameter>();
+    private readonly incompleteCalls = new Set<SdsAbstractCall>();
     private readonly nodeTypeCache: WorkspaceCache<string, Type>;
 
     constructor(services: SafeDsServices) {
@@ -301,18 +301,21 @@ export class SafeDsTypeComputer {
 
         // Lambda passed as argument
         if (isSdsArgument(containerOfLambda)) {
-            // Lookup parameter type in lambda unless the lambda is being computed. These contain the correct
-            // substitutions for type parameters.
-            if (!this.incompleteLambdaParameters.has(node)) {
-                return this.computeType(containingCallable);
-            }
-
             const parameter = this.nodeMapper.argumentToParameter(containerOfLambda);
             if (!parameter) {
                 return UnknownType;
             }
 
-            return this.computeType(parameter);
+            const unsubstitutedType = this.computeType(parameter);
+
+            // Substitute type parameters
+            const call = AstUtils.getContainerOfType(containerOfLambda, isSdsCall);
+            if (call) {
+                const substitutions = this.computeSubstitutionsForCall(call, containerOfLambda.$containerIndex);
+                return unsubstitutedType.substituteTypeParameters(substitutions);
+            }
+
+            return unsubstitutedType;
         }
 
         // Lambda passed as default value
@@ -569,29 +572,16 @@ export class SafeDsTypeComputer {
     }
 
     private computeTypeOfLambda(node: SdsLambda): Type {
-        // Remember lambda parameters
         const parameters = getParameters(node);
-        parameters.forEach((it) => {
-            this.incompleteLambdaParameters.add(it);
-        });
-
         const parameterEntries = parameters.map((it) => new NamedTupleEntry(it, it.name, this.computeType(it)));
         const resultEntries = this.buildLambdaResultEntries(node);
 
-        const unsubstitutedType = this.factory.createCallableType(
+        return this.factory.createCallableType(
             node,
             undefined,
             this.factory.createNamedTupleType(...parameterEntries),
             this.factory.createNamedTupleType(...resultEntries),
         );
-        const substitutions = this.computeSubstitutionsForLambda(node, unsubstitutedType);
-
-        // Forget lambda parameters
-        parameters.forEach((it) => {
-            this.incompleteLambdaParameters.delete(it);
-        });
-
-        return unsubstitutedType.substituteTypeParameters(substitutions);
     }
 
     private buildLambdaResultEntries(node: SdsLambda): NamedTupleEntry<SdsAbstractResult>[] {
@@ -843,23 +833,32 @@ export class SafeDsTypeComputer {
     /**
      * Computes substitutions for the type parameters of a callable in the context of a call.
      *
-     * @param node The call to compute substitutions for.
+     * @param node
+     * The call to compute substitutions for.
+     * @param argumentEndIndex
+     * The index of the first argument that should not be considered for the computation. If not specified, all
+     * arguments are considered.
+     *
      * @returns The computed substitutions for the type parameters of the callable.
      */
-    computeSubstitutionsForCall(node: SdsAbstractCall): TypeParameterSubstitutions {
-        return this.doComputeSubstitutionsForCall(node);
-    }
-
-    private doComputeSubstitutionsForCall(
+    computeSubstitutionsForCall(
         node: SdsAbstractCall,
-        precomputedArgumentTypes?: Map<AstNode | undefined, Type>,
+        argumentEndIndex: number | undefined = undefined,
     ): TypeParameterSubstitutions {
         // Compute substitutions for member access
         const substitutionsFromReceiver =
             isSdsCall(node) && isSdsMemberAccess(node.receiver)
                 ? this.computeSubstitutionsForMemberAccess(node.receiver)
                 : NO_SUBSTITUTIONS;
 
+        // Check if the call is already being computed
+        if (this.incompleteCalls.has(node)) {
+            return substitutionsFromReceiver;
+        }
+
+        // Remember call
+        this.incompleteCalls.add(node);
+
         // Compute substitutions for arguments
         const callable = this.nodeMapper.callToCallable(node);
         const typeParameters = getTypeParameters(callable);
@@ -868,24 +867,22 @@ export class SafeDsTypeComputer {
         }
 
         const parameters = getParameters(callable);
-        const args = getArguments(node);
+        const args = getArguments(node).slice(0, argumentEndIndex);
 
         const parametersToArguments = this.nodeMapper.parametersToArguments(parameters, args);
         const parameterTypesToArgumentTypes: [Type, Type][] = parameters.map((parameter) => {
             const argument = parametersToArguments.get(parameter);
-            return [
-                this.computeType(parameter.type),
-                // Use precomputed argument types (lambdas) if available. This prevents infinite recursion.
-                precomputedArgumentTypes?.get(argument?.value) ??
-                    this.computeType(argument?.value ?? parameter.defaultValue),
-            ];
+            return [this.computeType(parameter.type), this.computeType(argument?.value ?? parameter.defaultValue)];
         });
 
         const substitutionsFromArguments = this.computeSubstitutionsForArguments(
             typeParameters,
             parameterTypesToArgumentTypes,
         );
 
+        // Forget call
+        this.incompleteCalls.delete(node);
+
         return new Map([...substitutionsFromReceiver, ...substitutionsFromArguments]);
     }
 
@@ -918,22 +915,6 @@ export class SafeDsTypeComputer {
         return this.computeSubstitutionsForArguments(ownTypeParameters, ownTypesToOverriddenTypes);
     }
 
-    private computeSubstitutionsForLambda(node: SdsLambda, unsubstitutedType: Type): TypeParameterSubstitutions {
-        const containerOfLambda = node.$container;
-        if (!isSdsArgument(containerOfLambda)) {
-            return NO_SUBSTITUTIONS;
-        }
-
-        const containingCall = AstUtils.getContainerOfType(containerOfLambda, isSdsCall);
-        if (!containingCall) {
-            /* c8 ignore next 2 */
-            return NO_SUBSTITUTIONS;
-        }
-
-        const precomputedArgumentTypes = new Map([[node, unsubstitutedType]]);
-        return this.doComputeSubstitutionsForCall(containingCall, precomputedArgumentTypes);
-    }
-
     private computeSubstitutionsForMemberAccess(node: SdsMemberAccess): TypeParameterSubstitutions {
         const receiverType = this.computeType(node.receiver);
         if (receiverType instanceof ClassType) {

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

@@ -51,7 +51,7 @@ export const argumentTypesMustMatchParameterTypes = (services: SafeDsServices) =
                 return;
             }
 
-            const argumentType = typeComputer.computeType(argument).substituteTypeParameters(substitutions);
+            const argumentType = typeComputer.computeType(argument);
             const parameterType = typeComputer.computeType(parameter).substituteTypeParameters(substitutions);
 
             if (!typeChecker.isSubtypeOf(argumentType, parameterType, { ignoreParameterNames: true })) {

packages/safe-ds-lang/tests/helpers/nodeFinder.test.ts

@@ -65,14 +65,14 @@ describe('getNodeOfType', async () => {
 
     it('should throw if no node is found', async () => {
         const code = '';
-        expect(async () => {
+        await expect(async () => {
             await getNodeOfType(services, code, isSdsClass);
         }).rejects.toThrowErrorMatchingSnapshot();
     });
 
     it('should throw if not enough nodes are found', async () => {
         const code = `class C`;
-        expect(async () => {
+        await expect(async () => {
             await getNodeOfType(services, code, isSdsClass, 1);
         }).rejects.toThrowErrorMatchingSnapshot();
     });