feat: error if placeholder is alias for parameter or placeholder (#628)

Closes #564
Closes partially #543

### Summary of Changes

To provide a cleaner graphical view, this PR makes it an error if a
placeholder just acts as an alias for another placeholder or a
parameter.

---------

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

language-configuration.json

@@ -4,26 +4,28 @@
         "blockComment": ["/*", "*/"]
     },
     "brackets": [
+        ["(", ")"],
         ["{", "}"],
         ["[", "]"],
-        ["(", ")"],
+        ["<", ">"],
         ["»", "«"]
     ],
     "autoClosingPairs": [
+        ["(", ")"],
         ["{", "}"],
         ["[", "]"],
-        ["(", ")"],
-        ["»", "«"],
+        ["<", ">"],
         ["\"", "\""],
-        ["`", "`"]
+        ["`", "`"],
+        ["»", "«"]
     ],
     "surroundingPairs": [
+        ["(", ")"],
         ["{", "}"],
         ["[", "]"],
-        ["(", ")"],
         ["<", ">"],
-        ["»", "«"],
         ["\"", "\""],
-        ["`", "`"]
+        ["`", "`"],
+        ["»", "«"]
     ]
 }

package.json

@@ -1,21 +1,59 @@
 {
     "name": "safe-ds",
-    "displayName": "safe-ds",
-    "description": "Statically checked Data Science programs.",
     "version": "0.1.0",
+    "preview": true,
+    "publisher": "Safe-DS",
+    "displayName": "Safe-DS",
+    "description": "Statically checked Data Science programs.",
+    "license": "MIT",
+    "categories": [
+        "Programming Languages",
+        "Machine Learning",
+        "Data Science"
+    ],
+    "keywords": [
+        "dsl",
+        "static checking"
+    ],
+    "galleryBanner": {
+        "color": "#e3e9e9"
+    },
+    "icon": "img/safe-ds_logo_rounded.png",
+    "homepage": "https://dsl.safeds.com",
+    "qna": "https://github.com/orgs/Safe-DS/discussions",
+    "bugs": {
+        "url": "https://github.com/Safe-DS/DSL/issues"
+    },
+    "repository": {
+        "type": "git",
+        "url": "https://github.com/Safe-DS/DSL.git"
+    },
+    "badges": [
+        {
+            "url": "https://github.com/Safe-DS/DSL/actions/workflows/main.yml/badge.svg",
+            "href": "https://github.com/Safe-DS/DSL/actions/workflows/main.yml",
+            "description": "Main"
+        },
+        {
+            "url": "https://codecov.io/gh/Safe-DS/DSL/branch/main/graph/badge.svg?token=ma0ytglhO1",
+            "href": "https://codecov.io/gh/Safe-DS/DSL",
+            "description": "codecov"
+        }
+    ],
     "engines": {
         "vscode": "^1.82.0"
     },
-    "categories": [
-        "Programming Languages"
-    ],
     "contributes": {
         "languages": [
             {
                 "id": "safe-ds",
                 "aliases": [
                     "Safe-DS",
-                    "safe-ds"
+                    "safe-ds",
+                    "SafeDS",
+                    "safeds",
+                    "SDS",
+                    "sds"
                 ],
                 "extensions": [
                     ".sdspipe",
@@ -33,14 +71,14 @@
             }
         ]
     },
+    "type": "module",
+    "main": "out/extension/main.cjs",
     "files": [
         "bin"
     ],
-    "type": "module",
     "bin": {
         "safe-ds-cli": "./bin/cli"
     },
-    "main": "out/extension/main.cjs",
     "scripts": {
         "vscode:prepublish": "npm run build && npm run lint",
         "build": "tsc -b tsconfig.json && node esbuild.mjs",

src/language/validation/other/declarations/placeholders.ts

@@ -1,11 +1,41 @@
-import { isSdsBlock, isSdsStatement, SdsPlaceholder } from '../../../generated/ast.js';
+import {
+    isSdsAssignment,
+    isSdsBlock,
+    isSdsParameter,
+    isSdsPlaceholder,
+    isSdsReference,
+    isSdsStatement,
+    SdsPlaceholder,
+} from '../../../generated/ast.js';
 import { getContainerOfType, ValidationAcceptor } from 'langium';
 import { SafeDsServices } from '../../../safe-ds-module.js';
 import { statementsOrEmpty } from '../../../helpers/nodeProperties.js';
 import { last } from 'radash';
 
+export const CODE_PLACEHOLDER_ALIAS = 'placeholder/alias';
 export const CODE_PLACEHOLDER_UNUSED = 'placeholder/unused';
 
+export const placeholdersMustNotBeAnAlias = (node: SdsPlaceholder, accept: ValidationAcceptor): void => {
+    if (node.$containerIndex ?? 0 > 0) {
+        return;
+    }
+
+    const containingAssignment = getContainerOfType(node, isSdsAssignment);
+    const rhs = containingAssignment?.expression;
+    if (!isSdsReference(rhs)) {
+        return;
+    }
+
+    const referenceTarget = rhs.target.ref;
+    if (isSdsParameter(referenceTarget) || isSdsPlaceholder(referenceTarget)) {
+        accept('error', 'Aliases are not allowed to provide a cleaner graphical view.', {
+            node,
+            property: 'name',
+            code: CODE_PLACEHOLDER_ALIAS,
+        });
+    }
+};
+
 export const placeholderShouldBeUsed =
     (services: SafeDsServices) => (node: SdsPlaceholder, accept: ValidationAcceptor) => {
         const usages = services.helpers.NodeMapper.placeholderToReferences(node);

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

@@ -61,7 +61,7 @@ import {
     namedTypeDeclarationShouldNotBeExperimental,
     referenceTargetShouldNotExperimental,
 } from './builtins/experimental.js';
-import { placeholderShouldBeUsed } from './other/declarations/placeholders.js';
+import { placeholderShouldBeUsed, placeholdersMustNotBeAnAlias } from './other/declarations/placeholders.js';
 import { segmentParameterShouldBeUsed, segmentResultMustBeAssignedExactlyOnce } from './other/declarations/segments.js';
 import { lambdaParameterMustNotHaveConstModifier } from './other/expressions/lambdas.js';
 import { indexedAccessesShouldBeUsedWithCaution } from './experimentalLanguageFeature.js';
@@ -139,7 +139,7 @@ export const registerValidationChecks = function (services: SafeDsServices) {
         ],
         SdsParameterList: [parameterListMustNotHaveRequiredParametersAfterOptionalParameters],
         SdsPipeline: [pipelineMustContainUniqueNames],
-        SdsPlaceholder: [placeholderShouldBeUsed(services)],
+        SdsPlaceholder: [placeholdersMustNotBeAnAlias, placeholderShouldBeUsed(services)],
         SdsReference: [
             referenceTargetMustNotBeAnnotationPipelineOrSchema,
             referenceTargetShouldNotBeDeprecated(services),

tests/resources/validation/other/declarations/placeholders/alias/main.sdstest

@@ -0,0 +1,52 @@
+package tests.validation.other.placeholder.alias
+
+annotation MyAnnotation
+
+class MyClass {
+    static attr myAttribute: Int
+
+    static fun myMethod()
+}
+
+enum MyEnum {
+    MyEnumVariant
+}
+
+fun myFunction()
+
+pipeline myPipeline {}
+
+schema MySchema {}
+
+segment mySegment1() {}
+
+segment mySegment2(myParameter: Int) {
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »myPlaceholder« = 1;
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »a« = MyAnnotation;
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »b« = MyClass.myAttribute;
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »c« = MyClass;
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »d« = MyEnum;
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »e« = MyEnum.MyEnumVariant;
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »f« = myFunction;
+    // $TEST$ error "Aliases are not allowed to provide a cleaner graphical view."
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »g1«, val »g2« = myParameter;
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »h« = myPipeline;
+    // $TEST$ error "Aliases are not allowed to provide a cleaner graphical view."
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »i1«, val »i2« = myPlaceholder;
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »j« = MySchema;
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »k« = mySegment1;
+    // $TEST$ no error "Aliases are not allowed to provide a cleaner graphical view."
+    val »l« = unresolved;
+}