test(tsconfig): add focused test for references with extends

Add a dedicated test (`references_with_extends`) and fixture
(`references-extends/`) that exercises the fix from the previous
commit in isolation: a single-level reference whose `baseUrl`/`paths`
are inherited via `extends "../tsconfig.base.json"`.

Without `merge_tsconfig_extends` being applied to the reference, the
test fails with `NotFound` — confirming the test would have caught
the latent extends-on-reference bug.

Also revert the `references-transitive` fixture so it focuses purely
on multi-level walking; the extends-merging behavior is now covered
by the new fixture and test.

Author: stormslowly

fixtures/tsconfig/cases/references-extends/app/aliased/index.ts

@@ -0,0 +1 @@
+export const from = "app";

fixtures/tsconfig/cases/references-extends/app/tsconfig.json

@@ -0,0 +1,9 @@
+{
+  "compilerOptions": {
+    "baseUrl": "./",
+    "paths": {
+      "@/*": ["./aliased/*"]
+    }
+  },
+  "references": [{ "path": "../project_b" }]
+}

fixtures/tsconfig/cases/references-extends/project_b/src/aliased/index.ts

@@ -0,0 +1 @@
+export const from = "project_b via extends";

fixtures/tsconfig/cases/references-extends/project_b/tsconfig.json

@@ -0,0 +1,7 @@
+{
+  "extends": "../tsconfig.base.json",
+  "compilerOptions": {
+    "composite": true,
+    "baseUrl": "./src"
+  }
+}

…references-transitive/tsconfig.base.json …es/references-extends/tsconfig.base.jsonfixtures/tsconfig/cases/references-transitive/tsconfig.base.json renamed to fixtures/tsconfig/cases/references-extends/tsconfig.base.json fixtures/tsconfig/cases/references-transitive/tsconfig.base.json renamed to fixtures/tsconfig/cases/references-extends/tsconfig.base.json

@@ -1,7 +1,9 @@
 {
-  "extends": "../tsconfig.base.json",
   "compilerOptions": {
     "composite": true,
-    "baseUrl": "./"
+    "baseUrl": "./",
+    "paths": {
+      "@/*": ["./aliased/*"]
+    }
   }
 }

fixtures/tsconfig/cases/references-transitive/project_c/tsconfig.json

@@ -228,3 +228,36 @@ async fn transitive_references() {
     assert_eq!(resolved_path, Ok(expected), "{request} from {path:?}");
   }
 }
+
+// When a project reference uses `extends` to inherit its `baseUrl`/`paths`
+// from a shared base config, those fields must be merged before the
+// reference is consulted for resolution. Without merging `extends` on
+// referenced configs, a request from inside `project_b` would see no
+// alias candidates and fail to resolve.
+#[tokio::test]
+async fn references_with_extends() {
+  let f = super::fixture_root().join("tsconfig/cases/references-extends");
+
+  let resolver = Resolver::new(ResolveOptions {
+    tsconfig: Some(TsconfigOptions {
+      config_file: f.join("app"),
+      references: TsconfigReferences::Auto,
+    }),
+    ..ResolveOptions::default()
+  });
+
+  // From project_b's directory, the inherited `paths` from
+  // ../tsconfig.base.json must apply (baseUrl ./src).
+  let resolved_path = resolver
+    .resolve(&f.join("project_b/src"), "@/index.ts")
+    .await
+    .map(|p| p.full_path());
+  assert_eq!(resolved_path, Ok(f.join("project_b/src/aliased/index.ts")));
+
+  // The entry tsconfig still uses its own `paths`.
+  let resolved_path = resolver
+    .resolve(&f.join("app"), "@/index.ts")
+    .await
+    .map(|p| p.full_path());
+  assert_eq!(resolved_path, Ok(f.join("app/aliased/index.ts")));
+}