M3: it reads now

Claven could colour code. It couldn’t read it. Those are different jobs, and the second one needs a separate program, a language server, that loads your project and knows what things actually mean.

That runs now. A TypeScript error underlines while you type, before you save. TypeScript only. The other nine languages still just get colour.

Two things went wrong on the way, both worth writing down.

My notes said use typescript-language-server. It can’t work here. It drives tsserver.js, and TypeScript 7 is the Go rewrite, so there is no tsserver.js anymore. It exits at startup saying it can’t find a valid TypeScript installation, which is true.

The fix would have been installing TypeScript 5 next to 7 just to feed the wrapper. Two compilers, and squiggles computed by a different one than my build uses. No thanks. TypeScript 7 ships its own server in the binary, so I used that instead. It agrees with npm run typecheck by construction.

Then I connected it and got nothing.

Server started. Initialised. Answered. No underlines. Turns out the client library waits for the server to announce problems, and TypeScript 7 doesn’t announce. It expects to be asked. The push fired once, empty. Asking directly returned the actual error immediately.

That’s the bit I want to remember. Not a crash. Not an error in a log. A connection that looked completely healthy and silently reported nothing. If I’d wired it up and glanced at a file that happened to be correct, I’d have called it done.

What’s actually verified: diagnostics. There’s a test that types an error into a buffer, never saves, and waits for the underline.

Completion, hover, go-to-definition, rename all came bundled with the connection. They should work. I haven’t driven them, so they’re claims.

Next language is cheap: install a server, add a line for its file extensions. The pipe is the part that took the week.

Later the same day

I went back to check the three I had called claims. Two of them worked. Hover returns a real signature. Completion offers things from the project.

Go to definition did nothing at all.

The bug was mine. TypeScript reports where things are defined using a lower case drive letter, file:///c%3A/.... I was sending C%3A. The client library works out whether a definition is in the file you already have open by comparing those two strings exactly, so mine never matched. A jump inside one file got treated as a jump into a different one, it went looking for a document nothing had heard of, and returned without doing anything.

No error. No log line. A key that did nothing.

One capital letter. And there is a comment in that function, written by me, saying this is exactly where Windows integrations go wrong.

The test that caught it was nearly useless. All it said was “cursor never moved”. Asking the server for a definition directly and reading the URI it handed back showed the problem in one line. Worth remembering which of those two is the better first move.

All four work now.