From 4b7cc78bb47b88ebd5d1da771aed81a04b80a4c2 Mon Sep 17 00:00:00 2001
From: Egoistian <ywkim0313@gmail.com>
Date: Sun, 24 May 2026 22:11:16 +0900
Subject: [PATCH 1/3] fix tsconfig selection for monorepos

---
 src/shared.ts | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/src/shared.ts b/src/shared.ts
index 0987256..4379a8b 100644
--- a/src/shared.ts
+++ b/src/shared.ts
@@ -6,23 +6,15 @@ import * as vscode from 'vscode'
 import type { FormatDiagnosticsHost } from 'typescript'
 
 import { log } from './logger'
+import { findClosestTsconfig } from './tsconfigSelection'
 
-export async function getTsconfigFile(path: string) {
-  let files = await vscode.workspace.findFiles('**/tsconfig.json', '**​/node_modules/**')
-  files = files.sort((a, b) => b.fsPath.length - a.fsPath.length)
-    .filter(p => !p.fsPath.includes('node_modules'))
+export async function getTsconfigFile(filePath: string) {
+  const files = await vscode.workspace.findFiles('**/tsconfig.json', '**​/node_modules/**')
+  const tsconfigPath = findClosestTsconfig(filePath, files.map(file => file.fsPath))
 
-  log({ path, files })
+  log({ path: filePath, files, tsconfigPath })
 
-  const pathSegments = path.split('/')
-  for (let i = pathSegments.length; i > 0; i--) {
-    const path = pathSegments.slice(0, i).join('/')
-    const tsConfigFile = files.find(file => file.fsPath.startsWith(path))
-    if (tsConfigFile)
-      return tsConfigFile
-  }
-
-  return files[0]
+  return files.find(file => file.fsPath === tsconfigPath) ?? files[0]
 }
 
 const formatDiagnosticsHost: FormatDiagnosticsHost = {

From b992f06053a8e3e6b77cf8d71a1829c469ee99fd Mon Sep 17 00:00:00 2001
From: Egoistian <ywkim0313@gmail.com>
Date: Sun, 24 May 2026 22:11:29 +0900
Subject: [PATCH 2/3] add tsconfig selection helper

---
 src/tsconfigSelection.ts | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)
 create mode 100644 src/tsconfigSelection.ts

diff --git a/src/tsconfigSelection.ts b/src/tsconfigSelection.ts
new file mode 100644
index 0000000..c09b993
--- /dev/null
+++ b/src/tsconfigSelection.ts
@@ -0,0 +1,21 @@
+import path from 'node:path'
+
+export function findClosestTsconfig(filePath: string, tsconfigPaths: string[]): string | undefined {
+  const normalizedFilePath = normalizePath(filePath)
+  const candidates = tsconfigPaths
+    .filter(tsconfigPath => !isNodeModulesPath(tsconfigPath))
+    .sort((a, b) => b.length - a.length)
+
+  return candidates.find((tsconfigPath) => {
+    const configDirectory = normalizePath(path.dirname(tsconfigPath))
+    return normalizedFilePath === configDirectory || normalizedFilePath.startsWith(`${configDirectory}/`)
+  }) ?? candidates[0]
+}
+
+function normalizePath(filePath: string) {
+  return filePath.replaceAll('\\', '/').replace(/\/+$/, '')
+}
+
+function isNodeModulesPath(filePath: string) {
+  return normalizePath(filePath).split('/').includes('node_modules')
+}

From 72aeeaf113d4735ef1eee7c2d6c41d96648b99fe Mon Sep 17 00:00:00 2001
From: Egoistian <ywkim0313@gmail.com>
Date: Sun, 24 May 2026 22:11:46 +0900
Subject: [PATCH 3/3] test tsconfig selection for monorepos

---
 test/tsconfigSelection.test.ts | 45 ++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 test/tsconfigSelection.test.ts

diff --git a/test/tsconfigSelection.test.ts b/test/tsconfigSelection.test.ts
new file mode 100644
index 0000000..7b7d04b
--- /dev/null
+++ b/test/tsconfigSelection.test.ts
@@ -0,0 +1,45 @@
+import { describe, expect, it } from 'vitest'
+
+import { findClosestTsconfig } from '../src/tsconfigSelection'
+
+describe('findClosestTsconfig', () => {
+  it('selects the nearest tsconfig that contains the target file', () => {
+    expect(findClosestTsconfig(
+      '/repo/packages/app/src/index.ts',
+      [
+        '/repo/tsconfig.json',
+        '/repo/packages/app/tsconfig.json',
+      ],
+    )).toBe('/repo/packages/app/tsconfig.json')
+  })
+
+  it('does not select a sibling package tsconfig for a package without one', () => {
+    expect(findClosestTsconfig(
+      '/repo/packages/app-b/src/index.ts',
+      [
+        '/repo/tsconfig.json',
+        '/repo/packages/app-a/tsconfig.json',
+      ],
+    )).toBe('/repo/tsconfig.json')
+  })
+
+  it('ignores node_modules tsconfig files', () => {
+    expect(findClosestTsconfig(
+      '/repo/packages/app/src/index.ts',
+      [
+        '/repo/packages/app/node_modules/some-package/tsconfig.json',
+        '/repo/tsconfig.json',
+      ],
+    )).toBe('/repo/tsconfig.json')
+  })
+
+  it('handles Windows-style paths', () => {
+    expect(findClosestTsconfig(
+      'C:\\repo\\packages\\app\\src\\index.ts',
+      [
+        'C:\\repo\\tsconfig.json',
+        'C:\\repo\\packages\\app\\tsconfig.json',
+      ],
+    )).toBe('C:\\repo\\packages\\app\\tsconfig.json')
+  })
+})