fix: keep the case of Svelte file paths with --tsgo-experimental-api

.changeset/tsgo-api-file-casing.md

@@ -0,0 +1,6 @@
+---
+'svelte-language-server': patch
+'svelte-check': patch
+---
+
+fix: report Svelte compiler and CSS diagnostics under the file's real path with `--tsgo-experimental-api` on case-insensitive file systems

packages/language-server/src/plugins/typescript-go/features/DiagnosticsProvider.ts

@@ -193,7 +193,10 @@ export class SvelteCheckTSGoDiagnosticsProvider implements DiagnosticsProvider {
     }
 
     getAllSvelteFiles(): string[] {
-        return Array.from(this.files.keys()).filter(isSvelteFilePath);
+        // not the keys, which are lowercase on case-insensitive file systems
+        return Array.from(this.files.values(), (snapshot) => snapshot.filePath).filter(
+            isSvelteFilePath
+        );
     }
 
     mapAndFilterDiagnostics(

packages/language-server/test/plugins/typescript-go/features/diagnostics/index.test.ts

@@ -12,6 +12,7 @@ import { Document } from '../../../../../src/lib/documents';
 import ts from 'typescript';
 import { getPackageInfo } from '../../../../../src/importPackage';
 import assert from 'assert';
+import sinon from 'sinon';
 
 const isSvelte5Plus = Number(VERSION.split('.')[0]) >= 5;
 
@@ -40,6 +41,32 @@ describe('SvelteCheckTSGoDiagnosticsProvider', function () {
         workspaceDir: fixturesDir
     });
 
+    afterEach(() => sinon.restore());
+
+    it('returns Svelte file paths in their original case', async () => {
+        const syncApi = await import('@typescript/native-preview/unstable/sync');
+        const tsAst = await import('@typescript/native-preview/unstable/ast');
+        const tsconfig = path.join(__dirname, '../../testfiles/tsconfig.json');
+        // The file map lowercases its keys on case-insensitive file systems
+        sinon.stub(ts.sys, 'useCaseSensitiveFileNames').value(false);
+        const service = new SvelteCheckTSGoDiagnosticsProvider(
+            syncApi,
+            tsAst,
+            tsconfig,
+            'svelte2tsx',
+            (filePath, content) => new Document(pathToUrl(filePath), content)
+        );
+        sinon.restore();
+        try {
+            await service.getProject();
+            assert.deepStrictEqual(service.getAllSvelteFiles(), [
+                normalizePath(path.join(path.dirname(tsconfig), 'Upper.svelte'))
+            ]);
+        } finally {
+            service.dispose();
+        }
+    });
+
     after(() => {
         for (const provider of providerPool.values()) {
             provider.dispose();

packages/language-server/test/plugins/typescript-go/testfiles/Upper.svelte

@@ -0,0 +1,3 @@
+<script lang="ts">
+    export const value = 1;
+</script>

packages/language-server/test/plugins/typescript-go/testfiles/tsconfig.json

@@ -0,0 +1,3 @@
+{
+    "compilerOptions": { "strict": true, "types": [] }
+}