VS Code with stdin/out .exe server on Windows - visual-studio-code

Question

I have an LSP server that works fine with VS 2019 IDE. I am now trying to get it to work with VSCode. I wrote a simple extension for VSCode that was working with the server at one point, but VSCode is now not working at all. So, I decided to write a simple C program that simply reads stdin and echos the characters to stderr, not expecting it to work, but to verify that VSCode is at least trying to communicate with the server. As with my original server, this program receives absolutely nothing: VSCode is not sending any packets to the server, and I don't know why.
Here is the simple "echo" server code. All it does is read stdin one character indefinitely then echo the char more or less to stderr, flush()ing each time.
#include <iostream>
#include <stdio.h>
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <io.h>
int main()
{
for (;;)
{
char buf[10];
int readc = _read(0, buf, 1);
fprintf(stderr, "%d\n", buf[0]);
fflush(stderr);
}
return 0;
}
Here is a stripped-down VSCode client extension, derived from the doc, which so happens to provide zero information on spawning a server as a process. This calls spawn() of the server with a window.
export function activate(context: vscode.ExtensionContext) {
const server: vscodelc.Executable = {
command: `C:/Users/kenne/source/repos/ConsoleApplication1/Debug/ConsoleApplication1.exe`,
args: [],
options: {shell: true, detached: true }
};
const serverOptions: vscodelc.ServerOptions = server;
let clientOptions: vscodelc.LanguageClientOptions = {
// Register the server for plain text documents
documentSelector: [{ scheme: 'file', language: 'plaintext' }]
};
const client = new vscodelc.LanguageClient('Antlr Language Server', serverOptions, clientOptions);
console.log('Antlr Language Server is now active!');
client.start();
}
(Via debugging, I figured out that I needed options: {shell: true, detached: true } in the ServerOptions struct to make spawn() create a detached window for the process.) Running the client, the server is spawned with a window, but there is indeed no characters written to the server, even for the simple C "echo" program. In the debugger, I even see that write() is called in the client code, into the json write code, and then into the Node write code. For the VS2019 IDE, this all works perfectly fine.
Does anyone have any ideas on how to get an executable server that uses stdin/stdout to work with VSCode?

Answer 1

The answer is that the tables that the package.json file were messed up. It contains tables required for the server: "activationEvents" describes all the languages supported; "languages" associate a file extension with a language. In addition, the language table is duplicated in the LanguageClientOptions in the activate() function. Without these tables, VSCode may not send an open file request to the LSP server, or even not start the LSP server. In addition, there is a bug in libuv that prevents "windowHidden" to not be processed correctly for Windows. Therefore, the server process cannot be created with a window until fixed. Instead, send server debugging output to a file. The server now works great with VSCode for Antlr2, 3, 4, Bison, and W3C EBNF.