fix: Support additional extends package patterns

src/index.ts

@@ -31,7 +31,40 @@ const resolveTsConfigFromFile = (cwd: string, filename: string) => {
 const resolveTsConfigFromExtends = (cwd: string, name: string) => {
   if (path.isAbsolute(name)) return fs.existsSync(name) ? name : null
   if (name.startsWith(".")) return findUp(name, cwd)
-  const id = req.resolve(name, { paths: [cwd] })
+  let id: string | null = null
+  try {
+    id = req.resolve(name, { paths: [cwd] })
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code === "MODULE_NOT_FOUND") {
+      // config package did _not_ use pkg.main field
+      const nameParts = name.split("/")
+      if (
+        (name.startsWith("@") && nameParts.length === 2) ||
+        nameParts.length === 1
+      ) {
+        // a module (with optional scope) lacking subpath
+        const pkgJsonPath = req.resolve(path.join(name, "package.json"), {
+          paths: [cwd],
+        })
+        const pkgManifest = req(pkgJsonPath) as { tsconfig?: string }
+        // use explicit pkg.tsconfig or implicit "index" {pkgroot}/tsconfig.json
+        id = req.resolve(
+          path.join(
+            name,
+            pkgManifest.tsconfig ? pkgManifest.tsconfig : "tsconfig.json",
+          ),
+          { paths: [cwd] },
+        )
+      } else {
+        // a subpath directory, all others are handled in try block
+        id = req.resolve([...nameParts, "tsconfig.json"].join("/"), {
+          paths: [cwd],
+        })
+      }
+    } else {
+      throw error
+    }
+  }
   return id
 }
 

test/fixtures/extends-package-explicit/no-extn.json

@@ -0,0 +1,3 @@
+{
+  "extends": "tsconfig-pkg-explicit/other"
+}

test/fixtures/extends-package-explicit/subpath.json

@@ -0,0 +1,3 @@
+{
+  "extends": "tsconfig-pkg-explicit/other.json"
+}

test/fixtures/extends-package-explicit/tsconfig.json

@@ -0,0 +1,3 @@
+{
+  "extends": "tsconfig-pkg-explicit"
+}

test/fixtures/extends-package-implicit/no-extn.json

@@ -0,0 +1,3 @@
+{
+  "extends": "tsconfig-pkg-implicit/other"
+}

test/fixtures/extends-package-implicit/subpath.json

@@ -0,0 +1,4 @@
+{
+  "extends": "tsconfig-pkg-implicit/other/config"
+}
+

test/fixtures/extends-package-implicit/tsconfig.json

@@ -0,0 +1,3 @@
+{
+  "extends": "tsconfig-pkg-implicit"
+}

test/index.test.ts

@@ -26,6 +26,48 @@ test("extends package", () => {
   ])
 })
 
+test("extends package with explicit tsconfig", () => {
+  const loaded = loadTsConfig(fixture("extends-package-explicit"))
+  expect(loaded?.data.files).toEqual(["explicit"])
+})
+
+test("extends package subpath file without extension", () => {
+  const loaded = loadTsConfig(
+    fixture("extends-package-explicit"),
+    "no-extn.json",
+  )
+  expect(loaded?.data.files).toEqual(["other-file"])
+})
+
+test("extends package subpath file with extension", () => {
+  const loaded = loadTsConfig(
+    fixture("extends-package-explicit"),
+    "subpath.json",
+  )
+  expect(loaded?.data.files).toEqual(["other-file"])
+})
+
+test("extends package with implicit tsconfig", () => {
+  const loaded = loadTsConfig(fixture("extends-package-implicit"))
+  expect(loaded?.data.files).toEqual(["implicit"])
+})
+
+test("extends package with implicit subpath directory", () => {
+  const loaded = loadTsConfig(
+    fixture("extends-package-implicit"),
+    "no-extn.json",
+  )
+  expect(loaded?.data.files).toEqual(["other-directory"])
+})
+
+test("extends package with implicit file subpath", () => {
+  const loaded = loadTsConfig(
+    fixture("extends-package-implicit"),
+    "subpath.json",
+  )
+  expect(loaded?.data.files).toEqual(["other-directory-config"])
+})
+
 test("find nearest file", () => {
   expect(loadTsConfig(fixture("find-nearest/nested/dir"))).not.toBe(null)
 })