feat: show info if unnecessary syntax is used (#566)

Closes partially #543

### Summary of Changes

Show an info if one of the following can be removed:
* assignment (only wildcards as assignees)
* body of class/enum
* parameter list of annotation/enum variant
* result list of function/segment
* type parameter list of class/enum variant/function
* union type (singular type argument)

---------

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

src/language/validation/names.ts

@@ -0,0 +1,100 @@
+import { SdsDeclaration } from '../generated/ast.js';
+import { ValidationAcceptor } from 'langium';
+
+export const CODE_NAMES_BLOCK_LAMBDA_PREFIX = 'names/block-lambda-prefix';
+export const CODE_NAMES_CASING = 'names/casing';
+
+export const nameMustNotStartWithBlockLambdaPrefix = (node: SdsDeclaration, accept: ValidationAcceptor) => {
+    const name = node.name ?? '';
+    const blockLambdaPrefix = '__block_lambda_';
+    if (name.startsWith(blockLambdaPrefix)) {
+        accept(
+            'error',
+            "Names of declarations must not start with '__block_lambda_'. This is reserved for code generation of block lambdas.",
+            {
+                node,
+                property: 'name',
+                code: CODE_NAMES_BLOCK_LAMBDA_PREFIX,
+            },
+        );
+    }
+};
+
+export const nameShouldHaveCorrectCasing = (node: SdsDeclaration, accept: ValidationAcceptor): void => {
+    switch (node.$type) {
+        case 'SdsAnnotation':
+            return nameShouldBeUpperCamelCase(node, 'annotations', accept);
+        case 'SdsAttribute':
+            return nameShouldBeLowerCamelCase(node, 'attributes', accept);
+        case 'SdsBlockLambdaResult':
+            return nameShouldBeLowerCamelCase(node, 'block lambda results', accept);
+        case 'SdsClass':
+            return nameShouldBeUpperCamelCase(node, 'classes', accept);
+        case 'SdsEnum':
+            return nameShouldBeUpperCamelCase(node, 'enums', accept);
+        case 'SdsEnumVariant':
+            return nameShouldBeUpperCamelCase(node, 'enum variants', accept);
+        case 'SdsFunction':
+            return nameShouldBeLowerCamelCase(node, 'functions', accept);
+        case 'SdsModule':
+            const name = node.name ?? '';
+            const segments = name.split('.');
+            if (name !== '' && !segments.every(isLowerCamelCase)) {
+                accept('warning', 'All segments of the qualified name of a package should be lowerCamelCase.', {
+                    node,
+                    property: 'name',
+                    code: CODE_NAMES_CASING,
+                });
+            }
+            return;
+        case 'SdsParameter':
+            return nameShouldBeLowerCamelCase(node, 'parameters', accept);
+        case 'SdsPipeline':
+            return nameShouldBeLowerCamelCase(node, 'pipelines', accept);
+        case 'SdsPlaceholder':
+            return nameShouldBeLowerCamelCase(node, 'placeholders', accept);
+        case 'SdsResult':
+            return nameShouldBeLowerCamelCase(node, 'results', accept);
+        case 'SdsSchema':
+            return nameShouldBeUpperCamelCase(node, 'schemas', accept);
+        case 'SdsSegment':
+            return nameShouldBeLowerCamelCase(node, 'segments', accept);
+        case 'SdsTypeParameter':
+            return nameShouldBeUpperCamelCase(node, 'type parameters', accept);
+    }
+};
+
+const nameShouldBeLowerCamelCase = (node: SdsDeclaration, nodeName: string, accept: ValidationAcceptor): void => {
+    const name = node.name ?? '';
+    if (!isLowerCamelCase(name)) {
+        acceptCasingWarning(node, nodeName, 'lowerCamelCase', accept);
+    }
+};
+
+const isLowerCamelCase = (name: string): boolean => {
+    return /^[a-z][a-zA-Z0-9]*$/gu.test(name);
+};
+
+const nameShouldBeUpperCamelCase = (node: SdsDeclaration, nodeName: string, accept: ValidationAcceptor): void => {
+    const name = node.name ?? '';
+    if (!isUpperCamelCase(name)) {
+        acceptCasingWarning(node, nodeName, 'UpperCamelCase', accept);
+    }
+};
+
+const isUpperCamelCase = (name: string): boolean => {
+    return /^[A-Z][a-zA-Z0-9]*$/gu.test(name);
+};
+
+const acceptCasingWarning = (
+    node: SdsDeclaration,
+    nodeName: string,
+    expectedCasing: string,
+    accept: ValidationAcceptor,
+) => {
+    accept('warning', `Names of ${nodeName} should be ${expectedCasing}.`, {
+        node,
+        property: 'name',
+        code: CODE_NAMES_CASING,
+    });
+};

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

@@ -1,7 +1,20 @@
 import { ValidationChecks } from 'langium';
 import { SafeDsAstType } from '../generated/ast.js';
 import type { SafeDsServices } from '../safe-ds-module.js';
-import { nameMustNotStartWithBlockLambdaPrefix, nameShouldHaveCorrectCasing } from './nameConvention.js';
+import { nameMustNotStartWithBlockLambdaPrefix, nameShouldHaveCorrectCasing } from './names.js';
+import {
+    annotationParameterListShouldNotBeEmpty,
+    assignmentShouldHaveMoreThanWildcardsAsAssignees,
+    classBodyShouldNotBeEmpty,
+    classTypeParameterListShouldNotBeEmpty,
+    enumBodyShouldNotBeEmpty,
+    enumVariantParameterListShouldNotBeEmpty,
+    enumVariantTypeParameterListShouldNotBeEmpty,
+    functionResultListShouldNotBeEmpty,
+    functionTypeParameterListShouldNotBeEmpty,
+    segmentResultListShouldNotBeEmpty,
+    unionTypeShouldNotHaveASingularTypeArgument,
+} from './unnecessarySyntax.js';
 
 /**
  * Register custom validation checks.
@@ -10,7 +23,15 @@ export const registerValidationChecks = function (services: SafeDsServices) {
     const registry = services.validation.ValidationRegistry;
     const validator = services.validation.SafeDsValidator;
     const checks: ValidationChecks<SafeDsAstType> = {
+        SdsAssignment: [assignmentShouldHaveMoreThanWildcardsAsAssignees],
+        SdsAnnotation: [annotationParameterListShouldNotBeEmpty],
+        SdsClass: [classBodyShouldNotBeEmpty, classTypeParameterListShouldNotBeEmpty],
         SdsDeclaration: [nameMustNotStartWithBlockLambdaPrefix, nameShouldHaveCorrectCasing],
+        SdsEnum: [enumBodyShouldNotBeEmpty],
+        SdsEnumVariant: [enumVariantParameterListShouldNotBeEmpty, enumVariantTypeParameterListShouldNotBeEmpty],
+        SdsFunction: [functionResultListShouldNotBeEmpty, functionTypeParameterListShouldNotBeEmpty],
+        SdsSegment: [segmentResultListShouldNotBeEmpty],
+        SdsUnionType: [unionTypeShouldNotHaveASingularTypeArgument],
     };
     registry.register(checks, validator);
 };