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 +80,11 @@ export default createRule('no-unused-props', {
 			return shouldIgnore(typeStr) || (symbolName ? shouldIgnore(symbolName) : false);
 		}
 
-		function isExternalType(type: ts.Type): boolean {
-			const symbol = type.getSymbol();
-			if (!symbol) return false;
-
+		function isInternalProperty(symbol: ts.Symbol): boolean {
 			const declarations = symbol.getDeclarations();
 			if (!declarations || declarations.length === 0) return false;
 
-			const sourceFile = declarations[0].getSourceFile();
-			return sourceFile.fileName !== fileName;
+			return declarations.every((decl) => decl.getSourceFile().fileName === fileName);
 		}
 
 		/**
@@ -200,7 +196,6 @@ export default createRule('no-unused-props', {
 			if (checkedTypes.has(typeStr)) return;
 			checkedTypes.add(typeStr);
 			if (shouldIgnoreType(type)) return;
-			if (!checkImportedTypes && isExternalType(type)) return;
 
 			const properties = typeChecker.getPropertiesOfType(type);
 			const baseTypes = type.getBaseTypes();
@@ -225,6 +220,7 @@ export default createRule('no-unused-props', {
 
 			for (const prop of properties) {
 				if (isBuiltInProperty(prop)) continue;
+				if (!checkImportedTypes && !isInternalProperty(prop)) continue;
 
 				const propName = prop.getName();
 				const currentPath = [...parentPath, propName];

packages/eslint-plugin-svelte/tests/fixtures/rules/no-unused-props/invalid/ignore-external-type-errors.yaml

@@ -0,0 +1,4 @@
+- message: "'child2' is an unused Props property."
+  line: 10
+  column: 6
+  suggestions: null

packages/eslint-plugin-svelte/tests/fixtures/rules/no-unused-props/invalid/ignore-external-type-input.svelte

@@ -0,0 +1,10 @@
+<script lang="ts">
+	import type { FooDTO } from './shared-types';
+
+	interface Props extends FooDTO {
+		child1: string;
+		child2: number;
+	}
+
+	let { foo, child1 }: Props = $props();
+</script>

packages/eslint-plugin-svelte/tests/fixtures/rules/no-unused-props/invalid/imported-type-check-errors.yaml

@@ -1,6 +1,4 @@
 - message: "'name' is an unused Props property."
   line: 6
   column: 6
-  endLine: 6
-  endColumn: 20
   suggestions: null

packages/eslint-plugin-svelte/tests/fixtures/rules/no-unused-props/invalid/shared-types.ts

@@ -1,3 +1,14 @@
 export interface BaseProps {
 	name: string;
 }
+
+export interface FooDTO {
+	foo: string;
+	bar: number;
+	baz: BazDTO;
+}
+
+interface BazDTO {
+	qux: string;
+	quux: number;
+}

packages/eslint-plugin-svelte/tests/fixtures/rules/no-unused-props/valid/ignore-external-type-input.svelte

@@ -0,0 +1,10 @@
+<script lang="ts">
+	import type { FooDTO } from './shared-types';
+
+	interface Props extends FooDTO {
+		child1: string;
+		child2: number;
+	}
+
+	let { foo, child1, child2 }: Props = $props();
+</script>

packages/eslint-plugin-svelte/tests/fixtures/rules/no-unused-props/valid/shared-types.ts

@@ -1,3 +1,14 @@
 export interface BaseProps {
 	name: string;
 }
+
+export interface FooDTO {
+	foo: string;
+	bar: number;
+	baz: BazDTO;
+}
+
+interface BazDTO {
+	qux: string;
+	quux: number;
+}