From dcb25a40ef3a6acb85dd46fe1cac587600a4e376 Mon Sep 17 00:00:00 2001
From: donkeyote <a_barsby@hotmail.com>
Date: Mon, 6 Apr 2026 15:31:33 +0100
Subject: [PATCH] fix: ensure test files are ignored when type checking
MIME-Version: 1.0
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Move test file exclusion filter to run before the TypeScript program is created, rather than filtering diagnostics after the emit.

Previously, test and mock files (__tests__, __mocks__, *.spec.*, *.test.*) were still compiled as part of the program — their errors were just suppressed. Now they are excluded from rootNames upfront, so they are never type-checked at all.
---
 .../next/src/lib/typescript/runTypeCheck.ts   | 23 ++++++++++---------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/packages/next/src/lib/typescript/runTypeCheck.ts b/packages/next/src/lib/typescript/runTypeCheck.ts
index e786c7d263e60b..6fe3742b8222a5 100644
--- a/packages/next/src/lib/typescript/runTypeCheck.ts
+++ b/packages/next/src/lib/typescript/runTypeCheck.ts
@@ -106,6 +106,18 @@ export async function runTypeCheck(
     })
   }
 
+  const ignoreRegex = [
+    // matches **/__(tests|mocks)__/**
+    /[\\/]__(?:tests|mocks)__[\\/]/,
+    // matches **/*.(spec|test).*
+    /(?<=[\\/.])(?:spec|test)\.[^\\/]+$/,
+  ]
+  const regexIgnoredFile = new RegExp(
+    ignoreRegex.map((r) => r.source).join('|')
+  )
+
+  fileNames = fileNames.filter((fileName) => !regexIgnoredFile.test(fileName))
+
   if (fileNames.length < 1) {
     return {
       hasWarnings: false,
@@ -150,20 +162,9 @@ export async function runTypeCheck(
 
   const result = program.emit()
 
-  const ignoreRegex = [
-    // matches **/__(tests|mocks)__/**
-    /[\\/]__(?:tests|mocks)__[\\/]/,
-    // matches **/*.(spec|test).*
-    /(?<=[\\/.])(?:spec|test)\.[^\\/]+$/,
-  ]
-  const regexIgnoredFile = new RegExp(
-    ignoreRegex.map((r) => r.source).join('|')
-  )
-
   const allDiagnostics = typescript
     .getPreEmitDiagnostics(program as import('typescript').Program)
     .concat(result.diagnostics)
-    .filter((d) => !(d.file && regexIgnoredFile.test(d.file.fileName)))
 
   const firstError =
     allDiagnostics.find(