feat: info if import alias can be removed (#637)

Closes #636

### Summary of Changes

Show an info if the import alias is identical to the declaration name.

---------

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

src/language/formatting/safe-ds-formatter.ts

@@ -42,6 +42,8 @@ export class SafeDsFormatter extends AbstractFormatter {
             this.formatSdsImportedDeclarationList(node);
         } else if (ast.isSdsImportedDeclaration(node)) {
             this.formatSdsImportedDeclaration(node);
+        } else if (ast.isSdsImportedDeclarationAlias(node)) {
+            this.formatSdsImportedDeclarationAlias(node);
         }
 
         // -----------------------------------------------------------------------------
@@ -297,7 +299,13 @@ export class SafeDsFormatter extends AbstractFormatter {
     private formatSdsImportedDeclaration(node: ast.SdsImportedDeclaration): void {
         const formatter = this.getNodeFormatter(node);
 
-        formatter.keyword('as').surround(Formatting.oneSpace());
+        formatter.property('alias').prepend(oneSpace());
+    }
+
+    private formatSdsImportedDeclarationAlias(node: ast.SdsImportedDeclarationAlias): void {
+        const formatter = this.getNodeFormatter(node);
+
+        formatter.keyword('as').append(oneSpace());
     }
 
     // -----------------------------------------------------------------------------

src/language/grammar/safe-ds.langium

@@ -78,11 +78,19 @@ SdsImportedDeclarationList returns SdsImportedDeclarationList:
 
 interface SdsImportedDeclaration extends SdsObject {
     declaration: @SdsModuleMember;
-    alias?: string;
+    alias?: SdsImportedDeclarationAlias;
 }
 
 SdsImportedDeclaration returns SdsImportedDeclaration:
-    declaration=[SdsModuleMember:ID] ('as' alias=ID)?
+    declaration=[SdsModuleMember:ID] alias=SdsImportedDeclarationAlias?
+;
+
+interface SdsImportedDeclarationAlias extends SdsObject {
+    alias: string;
+}
+
+SdsImportedDeclarationAlias returns SdsImportedDeclarationAlias:
+    {SdsImportedDeclarationAlias} 'as' alias=ID
 ;
 
 interface SdsWildcardImport extends SdsImport {}

src/language/scoping/safe-ds-scope-provider.ts

@@ -409,7 +409,7 @@ export class SafeDsScopeProvider extends DefaultScopeProvider {
                     }
 
                     if (importedDeclaration.alias) {
-                        result.push({ ...description, name: importedDeclaration.alias });
+                        result.push({ ...description, name: importedDeclaration.alias.alias });
                     } else {
                         result.push(description);
                     }

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

@@ -26,6 +26,7 @@ import {
     enumBodyShouldNotBeEmpty,
     enumVariantParameterListShouldNotBeEmpty,
     functionResultListShouldNotBeEmpty,
+    importedDeclarationAliasShouldDifferFromDeclarationName,
     memberAccessNullSafetyShouldBeNeeded,
     namedTypeTypeArgumentListShouldBeNeeded,
     segmentResultListShouldNotBeEmpty,
@@ -139,6 +140,7 @@ export const registerValidationChecks = function (services: SafeDsServices) {
         SdsExpressionLambda: [expressionLambdaMustContainUniqueNames],
         SdsFunction: [functionMustContainUniqueNames, functionResultListShouldNotBeEmpty],
         SdsImport: [importPackageMustExist(services), importPackageShouldNotBeEmpty(services)],
+        SdsImportedDeclaration: [importedDeclarationAliasShouldDifferFromDeclarationName],
         SdsIndexedAccess: [indexedAccessesShouldBeUsedWithCaution],
         SdsLambda: [lambdaParametersMustNotBeAnnotated, lambdaParameterMustNotHaveConstModifier],
         SdsMemberAccess: [

src/language/validation/style.ts

@@ -10,6 +10,7 @@ import {
     SdsEnumBody,
     SdsEnumVariant,
     SdsFunction,
+    SdsImportedDeclaration,
     SdsMemberAccess,
     SdsNamedType,
     SdsSegment,
@@ -28,6 +29,7 @@ export const CODE_STYLE_UNNECESSARY_BODY = 'style/unnecessary-body';
 export const CODE_STYLE_UNNECESSARY_CONST_MODIFIER = 'style/unnecessary-const-modifier';
 export const CODE_STYLE_UNNECESSARY_CONSTRAINT_LIST = 'style/unnecessary-constraint-list';
 export const CODE_STYLE_UNNECESSARY_ELVIS_OPERATOR = 'style/unnecessary-elvis-operator';
+export const CODE_STYLE_UNNECESSARY_IMPORT_ALIAS = 'style/unnecessary-import-alias';
 export const CODE_STYLE_UNNECESSARY_PARAMETER_LIST = 'style/unnecessary-parameter-list';
 export const CODE_STYLE_UNNECESSARY_RESULT_LIST = 'style/unnecessary-result-list';
 export const CODE_STYLE_UNNECESSARY_SAFE_ACCESS = 'style/unnecessary-safe-access';
@@ -150,6 +152,23 @@ export const constraintListShouldNotBeEmpty = (node: SdsConstraintList, accept:
     }
 };
 
+// -----------------------------------------------------------------------------
+// Unnecessary import alias
+// -----------------------------------------------------------------------------
+
+export const importedDeclarationAliasShouldDifferFromDeclarationName = (
+    node: SdsImportedDeclaration,
+    accept: ValidationAcceptor,
+) => {
+    if (node.alias && node.alias.alias === node.declaration.$refText) {
+        accept('info', 'This alias can be removed.', {
+            node,
+            property: 'alias',
+            code: CODE_STYLE_UNNECESSARY_IMPORT_ALIAS,
+        });
+    }
+};
+
 // -----------------------------------------------------------------------------
 // Unnecessary parameter lists
 // -----------------------------------------------------------------------------

tests/resources/validation/style/unnecessary import alias/main.sdstest

@@ -0,0 +1,7 @@
+package tests.validation.style.unnecessaryImportAlias
+
+// $TEST$ no info "This alias can be removed."
+from tests.validation.style.unnecessaryImportAlias.other import C »as D«
+// $TEST$ info "This alias can be removed."
+// $TEST$ info "This alias can be removed."
+from tests.validation.style.unnecessaryImportAlias.other import C »as C«, C »as C«

tests/resources/validation/style/unnecessary import alias/resources.sdstest

@@ -0,0 +1,3 @@
+package tests.validation.style.unnecessaryImportAlias.other
+
+class C