(fix) check path aliases

If a path alias starts with "/", it is recognized as an absolute path by the paths library. Therefore virtual svelte files with such paths were resolved with the normal tsSys. This fix adds an additional check for the path aliases.
sveltejs#468

packages/language-server/src/plugins/typescript/module-loader.ts

@@ -67,6 +67,7 @@ export function createSvelteModuleLoader(
 ) {
     const svelteSys = createSvelteSys(getSnapshot);
     const moduleCache = new ModuleResolutionCache();
+    const pathAliases = getPathAliases(compilerOptions.paths);
 
     return {
         fileExists: svelteSys.fileExists,
@@ -98,7 +99,7 @@ export function createSvelteModuleLoader(
     ): ts.ResolvedModule | undefined {
         // In the normal case, delegate to ts.resolveModuleName.
         // In the relative-imported.svelte case, delegate to our own svelte module loader.
-        if (isAbsolute(name) || !isSvelteFilePath(name)) {
+        if (isAbsolutePath(name) || !isSvelteFilePath(name)) {
             return ts.resolveModuleName(name, containingFile, compilerOptions, ts.sys)
                 .resolvedModule;
         }
@@ -122,4 +123,17 @@ export function createSvelteModuleLoader(
         };
         return resolvedSvelteModule;
     }
+
+    function isAbsolutePath(path: string) {
+        return isAbsolute(path) && !pathAliases.some((p) => path.startsWith(p));
+    }
+
+    function getPathAliases(paths: ts.MapLike<string[]> | undefined) {
+        return Object.keys(paths || {}).map((key) => {
+            if (key.endsWith('*')) {
+                key = key.substr(0, key.length - 1);
+            }
+            return key;
+        });
+    }
 }

packages/language-server/test/plugins/typescript/module-loader.test.ts

@@ -23,7 +23,7 @@ describe('createSvelteModuleLoader', () => {
         const svelteSys = <any>'svelteSys';
         sinon.stub(svS, 'createSvelteSys').returns(svelteSys);
 
-        const compilerOptions: ts.CompilerOptions = { strict: true };
+        const compilerOptions: ts.CompilerOptions = { strict: true, paths: { '/@/*': [] } };
         const moduleResolver = createSvelteModuleLoader(getSvelteSnapshotStub, compilerOptions);
 
         return {
@@ -55,6 +55,26 @@ describe('createSvelteModuleLoader', () => {
         ]);
     });
 
+    it('uses tsSys for normal files part of TS aliases', async () => {
+        const resolvedModule: ts.ResolvedModuleFull = {
+            extension: ts.Extension.Ts,
+            resolvedFileName: 'filename.ts',
+        };
+        const { resolveStub, moduleResolver, compilerOptions } = setup(resolvedModule);
+        const result = moduleResolver.resolveModuleNames(
+            ['/@/normal'],
+            'C:/somerepo/somefile.svelte',
+        );
+
+        assert.deepStrictEqual(result, [resolvedModule]);
+        assert.deepStrictEqual(resolveStub.getCall(0).args, [
+            '/@/normal',
+            'C:/somerepo/somefile.svelte',
+            compilerOptions,
+            ts.sys,
+        ]);
+    });
+
     it('uses svelte module loader for virtual svelte files', async () => {
         const resolvedModule: ts.ResolvedModuleFull = {
             extension: ts.Extension.Ts,
@@ -87,6 +107,38 @@ describe('createSvelteModuleLoader', () => {
         assert.deepStrictEqual(getSvelteSnapshotStub.getCall(0).args, ['filename.svelte']);
     });
 
+    it('uses svelte module loader for virtual svelte files with TS path aliases', async () => {
+        const resolvedModule: ts.ResolvedModuleFull = {
+            extension: ts.Extension.Ts,
+            resolvedFileName: 'filename.svelte.ts',
+        };
+        const {
+            resolveStub,
+            svelteSys,
+            moduleResolver,
+            compilerOptions,
+            getSvelteSnapshotStub,
+        } = setup(resolvedModule);
+        const result = moduleResolver.resolveModuleNames(
+            ['/@/svelte.svelte'],
+            'C:/somerepo/somefile.svelte',
+        );
+
+        assert.deepStrictEqual(result, [
+            <ts.ResolvedModuleFull>{
+                extension: ts.Extension.Jsx,
+                resolvedFileName: 'filename.svelte',
+            },
+        ]);
+        assert.deepStrictEqual(resolveStub.getCall(0).args, [
+            '/@/svelte.svelte',
+            'C:/somerepo/somefile.svelte',
+            compilerOptions,
+            svelteSys,
+        ]);
+        assert.deepStrictEqual(getSvelteSnapshotStub.getCall(0).args, ['filename.svelte']);
+    });
+
     it('uses cache if module was already resolved before', async () => {
         const resolvedModule: ts.ResolvedModuleFull = {
             extension: ts.Extension.Ts,