fix: correct detection of externally defined types in no-unused-props rule

Author: baseballyama

.changeset/plain-chairs-tie.md

@@ -0,0 +1,5 @@
+---
+'eslint-plugin-svelte': patch
+---
+
+fix: correct detection of externally defined types in `no-unused-props` rule

packages/eslint-plugin-svelte/src/rules/no-unused-props.ts

@@ -80,15 +80,18 @@ export default createRule('no-unused-props', {
 			return shouldIgnore(typeStr) || (symbolName ? shouldIgnore(symbolName) : false);
 		}
 
-		function isExternalType(type: ts.Type): boolean {
-			const symbol = type.getSymbol();
+		function isInternalType(type: ts.Type): boolean {
+			const symbol = type.getSymbol() ?? type.aliasSymbol;
 			if (!symbol) return false;
 
 			const declarations = symbol.getDeclarations();
 			if (!declarations || declarations.length === 0) return false;
 
-			const sourceFile = declarations[0].getSourceFile();
-			return sourceFile.fileName !== fileName;
+			const isSameFile = declarations.every((decl) => decl.getSourceFile().fileName === fileName);
+			if (!isSameFile) return false;
+
+			const baseTypes = type.getBaseTypes() ?? [];
+			return baseTypes.every((baseType) => isInternalType(baseType));
 		}
 
 		/**
@@ -200,7 +203,7 @@ export default createRule('no-unused-props', {
 			if (checkedTypes.has(typeStr)) return;
 			checkedTypes.add(typeStr);
 			if (shouldIgnoreType(type)) return;
-			if (!checkImportedTypes && isExternalType(type)) return;
+			if (!checkImportedTypes && !isInternalType(type)) return;
 
 			const properties = typeChecker.getPropertiesOfType(type);
 			const baseTypes = type.getBaseTypes();