feat: call graph computer (without closures) (#782)

### Summary of Changes

Implement a first version of the call graph computer that can handle
everything but closures. These require the partial evaluator and will be
done later.

---------

Co-authored-by: megalinter-bot <[email protected]>

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

@@ -0,0 +1,26 @@
+import { SdsCallable } from '../generated/ast.js';
+import { stream, Stream } from 'langium';
+
+export class CallGraph {
+    constructor(
+        readonly root: SdsCallable | undefined,
+        readonly children: CallGraph[],
+        readonly isRecursive: boolean = false,
+    ) {}
+
+    /**
+     * Traverses the call graph depth-first in pre-order and returns a stream of all callables that are called directly
+     * or indirectly.
+     */
+    streamCalledCallables(): Stream<SdsCallable | undefined> {
+        return stream(this.streamCalledCallablesGenerator());
+    }
+
+    private *streamCalledCallablesGenerator(): Generator<SdsCallable | undefined, void> {
+        yield this.root;
+
+        for (const child of this.children) {
+            yield* child.streamCalledCallablesGenerator();
+        }
+    }
+}

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

@@ -1,11 +1,60 @@
-import { AstNode, type AstNodeLocator, getDocument, streamAst, WorkspaceCache } from 'langium';
-import { isSdsCall, type SdsCall } from '../generated/ast.js';
+import {
+    AstNode,
+    type AstNodeLocator,
+    getContainerOfType,
+    getDocument,
+    isNamed,
+    stream,
+    streamAst,
+    WorkspaceCache,
+} from 'langium';
+import {
+    isSdsAnnotation,
+    isSdsBlockLambda,
+    isSdsCall,
+    isSdsCallable,
+    isSdsCallableType,
+    isSdsClass,
+    isSdsEnumVariant,
+    isSdsExpressionLambda,
+    isSdsFunction,
+    isSdsParameter,
+    isSdsSegment,
+    SdsArgument,
+    SdsBlockLambda,
+    SdsCall,
+    SdsCallable,
+    SdsClass,
+    SdsEnumVariant,
+    SdsExpression,
+    SdsExpressionLambda,
+    SdsFunction,
+    SdsParameter,
+    SdsSegment,
+} from '../generated/ast.js';
 import type { SafeDsNodeMapper } from '../helpers/safe-ds-node-mapper.js';
 import type { SafeDsServices } from '../safe-ds-module.js';
+import {
+    BlockLambdaClosure,
+    EvaluatedCallable,
+    ExpressionLambdaClosure,
+    NamedCallable,
+    ParameterSubstitutions,
+    substitutionsAreEqual,
+    UnknownEvaluatedNode,
+} from '../partialEvaluation/model.js';
+import { CallGraph } from './model.js';
+import { getArguments, getParameters } from '../helpers/nodeProperties.js';
+import { SafeDsTypeComputer } from '../typing/safe-ds-type-computer.js';
+import { CallableType, StaticType } from '../typing/model.js';
+import { isEmpty } from '../../helpers/collectionUtils.js';
+import { SafeDsPartialEvaluator } from '../partialEvaluation/safe-ds-partial-evaluator.js';
 
 export class SafeDsCallGraphComputer {
     private readonly astNodeLocator: AstNodeLocator;
     private readonly nodeMapper: SafeDsNodeMapper;
+    private readonly partialEvaluator: SafeDsPartialEvaluator;
+    private readonly typeComputer: SafeDsTypeComputer;
 
     /**
      * Stores the calls inside the node with the given ID.
@@ -15,11 +64,268 @@ export class SafeDsCallGraphComputer {
     constructor(services: SafeDsServices) {
         this.astNodeLocator = services.workspace.AstNodeLocator;
         this.nodeMapper = services.helpers.NodeMapper;
+        this.partialEvaluator = services.evaluation.PartialEvaluator;
+        this.typeComputer = services.types.TypeComputer;
 
         this.callCache = new WorkspaceCache(services.shared);
     }
 
-    getCalls(node: AstNode): SdsCall[] {
+    /**
+     * Returns whether the given call is recursive using the given parameter substitutions.
+     *
+     * @param node
+     * The call to check.
+     *
+     * @param substitutions
+     * The parameter substitutions to use. These are **not** the argument of the call, but the values of the parameters
+     * of any containing callables, i.e. the context of the call.
+     */
+    isRecursive(node: SdsCall, substitutions: ParameterSubstitutions = NO_SUBSTITUTIONS): boolean {
+        return this.getCallGraph(node, substitutions).isRecursive;
+    }
+
+    /**
+     * Returns a stream of all callables that are called directly or indirectly by the given call. The call graph is
+     * traversed depth-first. If a callable is called recursively, it is only included once again.
+     *
+     * @param node
+     * The call to check.
+     *
+     * @param substitutions
+     * The parameter substitutions to use. These are **not** the argument of the call, but the values of the parameters
+     * of any containing callables, i.e. the context of the call.
+     */
+    getCallGraph(node: SdsCall, substitutions: ParameterSubstitutions = NO_SUBSTITUTIONS): CallGraph {
+        const call = this.createSyntheticCallForCall(node, substitutions);
+        return this.getCallGraphWithRecursionCheck(call, []);
+    }
+
+    private getCallGraphWithRecursionCheck(syntheticCall: SyntheticCall, visited: SyntheticCall[]): CallGraph {
+        const evaluatedCallable = syntheticCall.callable;
+
+        // Handle unknown callables & recursive calls
+        if (!evaluatedCallable) {
+            return new CallGraph(undefined, [], false);
+        } else if (visited.some((it) => it.equals(syntheticCall))) {
+            return new CallGraph(evaluatedCallable.callable, [], true);
+        }
+
+        // Visit all calls in the callable
+        const newVisited = [...visited, syntheticCall];
+        const children = this.getExecutedCalls(syntheticCall).map((it) => {
+            return this.getCallGraphWithRecursionCheck(it, newVisited);
+        });
+
+        return new CallGraph(
+            evaluatedCallable.callable,
+            children,
+            children.some((it) => it.isRecursive),
+        );
+    }
+
+    private getExecutedCalls(syntheticCall: SyntheticCall): SyntheticCall[] {
+        if (!syntheticCall.callable) {
+            /* c8 ignore next 2 */
+            return [];
+        }
+
+        const callable = syntheticCall.callable.callable;
+        const substitutions = syntheticCall.substitutions;
+
+        if (isSdsBlockLambda(callable) || isSdsExpressionLambda(callable) || isSdsSegment(callable)) {
+            return this.getExecutedCallsInPipelineCallable(callable, substitutions);
+        } else if (isSdsClass(callable) || isSdsEnumVariant(callable) || isSdsFunction(callable)) {
+            return this.getExecutedCallsInStubCallable(callable, substitutions);
+        } else {
+            /* c8 ignore next 2 */
+            return [];
+        }
+    }
+
+    private getExecutedCallsInPipelineCallable(
+        callable: SdsBlockLambda | SdsExpressionLambda | SdsSegment,
+        substitutions: ParameterSubstitutions,
+    ): SyntheticCall[] {
+        const callsInDefaultValues = getParameters(callable).flatMap((it) => {
+            // The default value is only executed if no argument is passed for the parameter
+            if (it.defaultValue && !substitutions.has(it)) {
+                return this.getCalls(it.defaultValue);
+            } else {
+                return [];
+            }
+        });
+
+        let callsInBody: SdsCall[];
+        if (isSdsBlockLambda(callable)) {
+            callsInBody = this.getCalls(callable.body);
+        } else if (isSdsExpressionLambda(callable)) {
+            callsInBody = this.getCalls(callable.result);
+        } else {
+            callsInBody = this.getCalls(callable.body);
+        }
+
+        return [...callsInDefaultValues, ...callsInBody]
+            .filter((it) => getContainerOfType(it, isSdsCallable) === callable)
+            .map((it) => this.createSyntheticCallForCall(it, substitutions));
+    }
+
+    private getExecutedCallsInStubCallable(
+        callable: SdsClass | SdsEnumVariant | SdsFunction,
+        substitutions: ParameterSubstitutions,
+    ): SyntheticCall[] {
+        const callsInDefaultValues = getParameters(callable).flatMap((parameter) => {
+            // The default value is only executed if no argument is passed for the parameter
+            if (parameter.defaultValue && !substitutions.has(parameter)) {
+                // We assume all calls in the default value are executed
+                const calls = this.getCalls(parameter.defaultValue);
+                if (!isEmpty(calls)) {
+                    return calls.map((call) => this.createSyntheticCallForCall(call, substitutions));
+                }
+
+                // We assume a single callable as default value is executed
+                const evaluatedCallable = this.getEvaluatedCallable(parameter.defaultValue, substitutions);
+                if (evaluatedCallable) {
+                    return [this.createSyntheticCallForEvaluatedCallable(evaluatedCallable)];
+                }
+            }
+
+            return [];
+        });
+
+        const callablesInSubstitutions = stream(substitutions.values()).flatMap((it) => {
+            if (it instanceof EvaluatedCallable) {
+                return [this.createSyntheticCallForEvaluatedCallable(it)];
+            }
+
+            return [];
+        });
+
+        return [...callsInDefaultValues, ...callablesInSubstitutions];
+    }
+
+    private createSyntheticCallForCall(call: SdsCall, substitutions: ParameterSubstitutions): SyntheticCall {
+        const evaluatedCallable = this.getEvaluatedCallable(call.receiver, substitutions);
+        const newSubstitutions = this.getNewSubstitutions(evaluatedCallable, getArguments(call), substitutions);
+        return new SyntheticCall(evaluatedCallable, newSubstitutions);
+    }
+
+    private createSyntheticCallForEvaluatedCallable(evaluatedCallable: EvaluatedCallable): SyntheticCall {
+        return new SyntheticCall(evaluatedCallable, evaluatedCallable.substitutionsOnCreation);
+    }
+
+    private getEvaluatedCallable(
+        expression: SdsExpression,
+        substitutions: ParameterSubstitutions,
+    ): EvaluatedCallable | undefined {
+        // TODO use the partial evaluator here; necessary for closures
+        // const value = this.partialEvaluator.evaluate(expression, substitutions);
+        // if (value instanceof EvaluatedCallable) {
+        //     return value;
+        // }
+        //
+        // return undefined;
+
+        let callableOrParameter = this.getCallableOrParameter(expression);
+
+        if (!callableOrParameter || isSdsAnnotation(callableOrParameter) || isSdsCallableType(callableOrParameter)) {
+            return undefined;
+        } else if (isSdsParameter(callableOrParameter)) {
+            // Parameter is set explicitly
+            const substitution = substitutions.get(callableOrParameter);
+            if (substitution) {
+                if (substitution instanceof EvaluatedCallable) {
+                    return substitution;
+                } else {
+                    /* c8 ignore next 2 */
+                    return undefined;
+                }
+            }
+
+            // Parameter might have a default value
+            if (!callableOrParameter.defaultValue) {
+                return undefined;
+            }
+            return this.getEvaluatedCallable(callableOrParameter.defaultValue, substitutions);
+        } else if (isNamed(callableOrParameter)) {
+            return new NamedCallable(callableOrParameter);
+        } else if (isSdsBlockLambda(callableOrParameter)) {
+            return new BlockLambdaClosure(callableOrParameter, substitutions);
+        } else if (isSdsExpressionLambda(callableOrParameter)) {
+            return new ExpressionLambdaClosure(callableOrParameter, substitutions);
+        } else {
+            /* c8 ignore next 2 */
+            return undefined;
+        }
+    }
+
+    private getCallableOrParameter(expression: SdsExpression): SdsCallable | SdsParameter | undefined {
+        const type = this.typeComputer.computeType(expression);
+
+        if (type instanceof CallableType) {
+            return type.parameter ?? type.callable;
+        } else if (type instanceof StaticType) {
+            const declaration = type.instanceType.declaration;
+            if (isSdsCallable(declaration)) {
+                return declaration;
+            }
+        }
+
+        return undefined;
+    }
+
+    private getNewSubstitutions(
+        callable: EvaluatedCallable | undefined,
+        args: SdsArgument[],
+        substitutions: ParameterSubstitutions,
+    ): ParameterSubstitutions {
+        if (!callable) {
+            return NO_SUBSTITUTIONS;
+        }
+
+        // Substitutions on creation
+        const substitutionsOnCreation = callable.substitutionsOnCreation;
+
+        // Substitutions on call
+        const parameters = getParameters(callable?.callable);
+        const substitutionsOnCall = new Map(
+            args.flatMap((it) => {
+                // Ignore arguments that don't get assigned to a parameter
+                const parameterIndex = this.nodeMapper.argumentToParameter(it)?.$containerIndex ?? -1;
+                if (parameterIndex === -1) {
+                    /* c8 ignore next 2 */
+                    return [];
+                }
+
+                // argumentToParameter returns parameters of callable types. We have to remap this to parameter of the
+                // actual callable.
+                const parameter = parameters[parameterIndex];
+                if (!parameter) {
+                    /* c8 ignore next 2 */
+                    return [];
+                }
+
+                const value = this.getEvaluatedCallable(it.value, substitutions);
+                if (!value) {
+                    // We still have to remember that a value was passed, so the default value is not used
+                    return [[parameter, UnknownEvaluatedNode]];
+                }
+
+                return [[parameter, value]];
+            }),
+        );
+
+        return new Map([...substitutionsOnCreation, ...substitutionsOnCall]);
+    }
+
+    /**
+     * Returns all calls inside the given node. If the node is a call, it is included as well.
+     */
+    getCalls(node: AstNode | undefined): SdsCall[] {
+        if (!node) {
+            /* c8 ignore next 2 */
+            return [];
+        }
+
         const key = this.getNodeId(node);
         return this.callCache.get(key, () => streamAst(node).filter(isSdsCall).toArray());
     }
@@ -30,3 +336,21 @@ export class SafeDsCallGraphComputer {
         return `${documentUri}~${nodePath}`;
     }
 }
+
+class SyntheticCall {
+    constructor(
+        readonly callable: EvaluatedCallable | undefined,
+        readonly substitutions: ParameterSubstitutions,
+    ) {}
+
+    equals(other: SyntheticCall): boolean {
+        if (!this.callable) {
+            /* c8 ignore next 2 */
+            return !other.callable && substitutionsAreEqual(this.substitutions, other.substitutions);
+        }
+
+        return this.callable.equals(other.callable) && substitutionsAreEqual(this.substitutions, other.substitutions);
+    }
+}
+
+const NO_SUBSTITUTIONS: ParameterSubstitutions = new Map();