feat: ensure that all assignees get a value (#630)

Closes partially #543

### Summary of Changes

Show an error if an assignee might not get a value.

---------

Co-authored-by: megalinter-bot <129584137+megalinter-bot@users.noreply.github.com>

language-configuration.json

@@ -7,7 +7,6 @@
         ["(", ")"],
         ["{", "}"],
         ["[", "]"],
-        ["<", ">"],
         ["»", "«"]
     ],
     "autoClosingPairs": [

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

@@ -88,9 +88,9 @@ export class SafeDsTypeComputer {
     private readonly coreClasses: SafeDsClasses;
     private readonly nodeMapper: SafeDsNodeMapper;
 
-    readonly typeCache: WorkspaceCache<string, Type>;
+    private readonly typeCache: WorkspaceCache<string, Type>;
 
-    constructor(readonly services: SafeDsServices) {
+    constructor(services: SafeDsServices) {
         this.astNodeLocator = services.workspace.AstNodeLocator;
         this.coreClasses = services.builtins.Classes;
         this.nodeMapper = services.helpers.NodeMapper;

src/language/validation/other/expressions/references.ts

@@ -19,7 +19,6 @@ export const referenceMustNotBeFunctionPointer = (node: SdsReference, accept: Va
         return;
     }
 
-    //
     let container: AstNode | undefined = node.$container;
     if (isSdsMemberAccess(container) && node.$containerProperty === 'member') {
         container = container.$container;

src/language/validation/other/statements/assignments.ts

@@ -1,8 +1,24 @@
-import { isSdsPipeline, SdsYield } from '../../../generated/ast.js';
+import { isSdsPipeline, SdsAssignment, SdsYield } from '../../../generated/ast.js';
 import { getContainerOfType, ValidationAcceptor } from 'langium';
+import { SafeDsServices } from '../../../safe-ds-module.js';
+import { assigneesOrEmpty } from '../../../helpers/nodeProperties.js';
 
+export const CODE_ASSIGMENT_NOTHING_ASSIGNED = 'assignment/nothing-assigned';
 export const CODE_ASSIGMENT_YIELD_FORBIDDEN_IN_PIPELINE = 'assignment/yield-forbidden-in-pipeline';
 
+export const assignmentAssigneeMustGetValue =
+    (services: SafeDsServices) =>
+    (node: SdsAssignment, accept: ValidationAcceptor): void => {
+        for (const assignee of assigneesOrEmpty(node)) {
+            if (!services.helpers.NodeMapper.assigneeToAssignedObjectOrUndefined(assignee)) {
+                accept('error', 'No value is assigned to this assignee.', {
+                    node: assignee,
+                    code: CODE_ASSIGMENT_NOTHING_ASSIGNED,
+                });
+            }
+        }
+    };
+
 export const yieldMustNotBeUsedInPipeline = (node: SdsYield, accept: ValidationAcceptor): void => {
     const containingPipeline = getContainerOfType(node, isSdsPipeline);
 

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

@@ -33,7 +33,7 @@ import {
     unionTypeShouldNotHaveASingularTypeArgument,
 } from './style.js';
 import { templateStringMustHaveExpressionBetweenTwoStringParts } from './other/expressions/templateStrings.js';
-import { yieldMustNotBeUsedInPipeline } from './other/statements/assignments.js';
+import { assignmentAssigneeMustGetValue, yieldMustNotBeUsedInPipeline } from './other/statements/assignments.js';
 import { attributeMustHaveTypeHint, parameterMustHaveTypeHint, resultMustHaveTypeHint } from './types.js';
 import { moduleDeclarationsMustMatchFileKind, moduleWithDeclarationsMustStatePackage } from './other/modules.js';
 import { typeParameterConstraintLeftOperandMustBeOwnTypeParameter } from './other/declarations/typeParameterConstraints.js';
@@ -87,7 +87,7 @@ export const registerValidationChecks = function (services: SafeDsServices) {
             assigneeAssignedResultShouldNotBeDeprecated(services),
             assigneeAssignedResultShouldNotBeExperimental(services),
         ],
-        SdsAssignment: [assignmentShouldHaveMoreThanWildcardsAsAssignees],
+        SdsAssignment: [assignmentAssigneeMustGetValue(services), assignmentShouldHaveMoreThanWildcardsAsAssignees],
         SdsAnnotation: [
             annotationMustContainUniqueNames,
             annotationParameterListShouldNotBeEmpty,

tests/resources/validation/other/statements/assignments/nothing assigned/main.sdstest

@@ -0,0 +1,83 @@
+package tests.validation.other.statements.assignments.nothingAssigned
+
+fun noResults()
+fun oneResult() -> first: Int
+fun twoResults() -> (first: Int, second: Int)
+
+segment mySegment() -> (
+    r1: Any?,
+    r2: Any?,
+    r3: Any?,
+    r4: Any?,
+    r5: Any?,
+    r6: Any?,
+    r7: Any?,
+    r8: Any?,
+    r9: Any?,
+    r10: Any?,
+    r11: Any?,
+    r12: Any?,
+    r13: Any?,
+    r14: Any?,
+) {
+    // $TEST$ error "No value is assigned to this assignee."
+    »_« = noResults();
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »_«, »_« = oneResult();
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »_«, »_«, »_« = twoResults();
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »_«, »_« = 1;
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »_«, »_« = unresolved;
+    // $TEST$ error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »_«, »_« = unresolved();
+
+    // $TEST$ error "No value is assigned to this assignee."
+    »val a« = noResults();
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »val b«, »val c« = oneResult();
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »val d«, »val e«, »val f« = twoResults();
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »val g«, »val h« = 1;
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »val i«, »val j« = unresolved;
+    // $TEST$ error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »val k«, »val l« = unresolved();
+
+    // $TEST$ error "No value is assigned to this assignee."
+    »yield r1« = noResults();
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »yield r2«, »yield r3« = oneResult();
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »yield r4«, »yield r5«, »yield r6« = twoResults();
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »yield r7«, »yield r8« = 1;
+    // $TEST$ no error "No value is assigned to this assignee."
+    »yield r9« = oneResult();
+    // $TEST$ no error "No value is assigned to this assignee."
+    »yield r10« = twoResults();
+    // $TEST$ no error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »yield r11«, »yield r12« = unresolved;
+    // $TEST$ error "No value is assigned to this assignee."
+    // $TEST$ error "No value is assigned to this assignee."
+    »yield r13«, »yield r14« = unresolved();
+}