tsc --watch never recompiles on macOS since 7.1.0-dev.20260811.1

[leonidaz]

🔎 Search Terms

• --watch never recompiles
• tsc --watch macOS no file change detected
• --build --watch macOS regression 7.1.0-dev.20260811.1

🕗 Version & Regression Information

• Broken in every nightly from 7.1.0-dev.20260811.1 through 7.1.0-dev.20260919.1 (@typescript/typescript-darwin-x64)
• Works in 7.1.0-dev.20260810.1 and in @typescript/native-preview 7.0.0-dev.20260707.2
• Bisected across the published nightlies: last good 7.1.0-dev.20260810.1 (published 2026-08-10T08:17Z), first bad 7.1.0-dev.20260811.1 (published 2026-08-11T08:18Z)
• macOS 26.6.2 (x64, APFS); TypeScript 5.9.3 tsc --watch works in the same shell

Commits on main between the two nightly builds:

• 40af284 Handle extensionless root files gracefully instead of panicking (Handle extensionless root files gracefully instead of panicking typescript-go#4628)
• 5cad7ec Fall back to inotify when filesystem has errors in fanotify (fix watch in Docker) (Fall back to inotify when filesystem has errors in fanotify (fix watch in Docker) typescript-go#4661)
• b7045b4 Fix watch diagnostics when global declaration is removed (Fix watch diagnostics when global declaration is removed typescript-go#4848)
• 1adcc62 Preserve await context for exported classes in nested containers (Preserve await context for exported classes in nested containers typescript-go#4823)
• 3c315b7 Account nested declaration emits as emit time (Account nested declaration emits as emit time typescript-go#4557)
• a649b1f Remove macOS realpath fast path (Remove macOS realpath fast path typescript-go#4867)
• bbf7371 Port transpileModule, transpileDeclaration (Port transpileModule, transpileDeclaration typescript-go#4849)
• 56244eb Split heritage clause expression and type nodes (Split heritage clause expression and type nodes typescript-go#4797)

⏯ Playground Link

n/a (watch mode)

💻 Code

mkdir repro && cd repro
echo '{ "compilerOptions": { "strict": true, "noEmit": true }, "include": ["*.ts"] }' > tsconfig.json
echo 'export const a: number = 1;' > a.ts
tsc --watch --pretty false &
sleep 2
echo 'export const a: number = "x";' > a.ts
sleep 10

🙁 Actual behavior

11:33:16 AM - Starting compilation in watch mode...

11:33:16 AM - Found 0 errors. Watching for file changes.

Nothing else is ever printed. The edited file is not re-checked and TS2322 never appears. A second edit, creating a new b.ts, editing tsconfig.json and deleting a file are all ignored as well. tsc --build --watch behaves the same.

Things that make no difference:

• --watchFile fixedpollinginterval, dynamicprioritypolling, prioritypollinginterval, usefseventsonparentdirectory (and --watchDirectory fixedpollinginterval): the options are accepted, the behaviour is identical
• Directory shape: an all-lowercase directory with no symlink in its path (/private/tmp/tsrx-watch-lower), a mixed-case one (/private/tmp/tsrx-Watch-Upper), a path through the /tmp symlink, a path under $HOME, and a firmlink-prefixed path (/System/Volumes/Data/...) all fail the same way
• stdin: closed (/dev/null) or kept open as a pipe
• With or without a content mapper in the project

So this looks different from #64089 (dropped FSEvents when casing differs), although the regression window contains the realpath change that issue mentions (a649b1f).

On 7.1.0-dev.20260810.1 the same steps print File change detected. Starting incremental compilation... and the TS2322 error about 2 seconds after the edit.

🙂 Expected behavior

Watch mode recompiles after the edit and reports the error, as 7.1.0-dev.20260810.1 and TypeScript 5.9 do.

Additional information about the issue

Only macOS was tested (Intel, macOS 26.6.2). Found while building the .tsrx content mapper for TSRX (tsrx-org/tsrx#41), where the --watch test can only assert the initial compilation.