Could not locate the configured slint-lsp server binary at…

Error message

Could not locate the configured slint-lsp server binary at absolute path

What it means

When the user configures an absolute path override for the slint-lsp server binary, find_lsp_binary checks only that exact path. If the file does not exist there, it warns 'Could not locate the configured slint-lsp server binary at absolute path' and returns undefined, leaving the extension without a language server. This is a configuration-validation warning, not a runtime crash.

Solutions

Verify the configured absolute path exists and points to the slint-lsp executable (ls <path>)
Rebuild the binary with cargo build -p slint-lsp if it was removed
Correct the extension setting to the new/valid path
Remove the override so the extension falls back to bundled/PATH discovery

Example fix

// settings.json before (stale path)
{ "slint.lsp": "/home/me/old/target/debug/slint-lsp" }
// after (rebuilt path)
{ "slint.lsp": "/home/me/slint/target/debug/slint-lsp" }

Defensive patterns

Strategy: validation

Validate before calling

const p = vscode.workspace.getConfiguration('slint').get('lsp');
if (typeof p === 'string' && path.isAbsolute(p) && !existsSync(p)) vscode.window.showWarningMessage(`slint-lsp override does not exist: ${p}`);

Prevention

Use an absolute path only for binaries you know exist
Re-verify the override after cargo clean or machine changes
Point at the executable file, not its directory
Prefer PATH-based or bundled discovery over hardcoded paths

When it happens

Trigger: The slint.lsp binary override setting contains an absolute path whose file does not exist — e.g. typo in the path, binary deleted after a cargo clean, path pointing at the wrong machine/user directory, or pointing at a directory instead of the executable.

Common situations: Pointing at a target/debug directory wiped by 'cargo clean'; hardcoding a path from another OS or another developer's machine; the binary was renamed or a new version changed its location.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

AI-assisted analysis of slint-ui/slint@bb937076de (2026-09-16). Data as JSON: /api/errors/348c2365e4e38503. Report an issue: GitHub.

Appendix: source

Thrown at editors/vscode/src/extension.ts:143

            path.join(context.extensionPath, "bin", lsp_platform.program_name),
        ];

        const serverModule = lspSearchPaths.find((path) => existsSync(path));

        if (serverModule === undefined) {
            console.warn(
                "Could not locate slint-lsp server binary, neither in bundled bin/ directory nor relative in ../target",
            );
        }
        return serverModule;
    }

    if (path.isAbsolute(lsp_binary_path)) {
        // The slint-lsp override is a absolute path: Look in that path only
        if (existsSync(lsp_binary_path)) {
            return lsp_binary_path;
        }
        console.warn(
            "Could not locate the configured slint-lsp server binary at absolute path",
        );
        return undefined;
    }

    // The slint-lsp override is a relative path: Look relative to PATH
    const path_env = process.env.PATH?.split(path.delimiter).map((p) =>
        path.join(p, lsp_binary_path),
    );

    const serverModule = path_env?.find((path) => existsSync(path));
    if (serverModule === undefined) {
        console.warn(
            "Could not locate the configured slint-lsp server binary in PATH",
        );
    }
    return serverModule;
}

View on GitHub (pinned to bb937076de)