helix-editor/helix · error · anyhow::Error

Parser compilation failed. Stdout: {} Stderr: {}

Error message

Parser compilation failed.
Stdout: {}
Stderr: {}

What it means

Windows/MSVC branch of grammar compilation: the scanner file (scanner.cc/.cpp) is pre-compiled to an object with cl.exe (/nologo /LD /I<includes> /utf-8 /std:c++14 /c) before linking with the parser, and cl.exe exited non-zero. Stdout/stderr of the compiler are embedded so the real compiler diagnostic is in the message.

Source

Thrown at helix-loader/src/grammar.rs:634

                    cpp_command.env(key, value);
                }
                cpp_command.args(compiler.args());
                let object_file =
                    library_path.with_file_name(format!("{}_scanner.obj", &grammar.grammar_id));
                cpp_command
                    .args(["/nologo", "/LD", "/I"])
                    .arg(header_path)
                    .arg("/utf-8")
                    .arg("/std:c++14")
                    .arg(format!("/Fo{}", object_file.display()))
                    .arg("/c")
                    .arg(scanner_path);
                let output = cpp_command
                    .output()
                    .context("Failed to execute C++ compiler")?;

                if !output.status.success() {
                    return Err(anyhow!(
                        "Parser compilation failed.\nStdout: {}\nStderr: {}",
                        String::from_utf8_lossy(&output.stdout),
                        String::from_utf8_lossy(&output.stderr)
                    ));
                }
                command.arg(&object_file);
                _path_guard = TempPath::try_from_path(object_file).unwrap();
            }
        }

        command
            .arg(parser_path)
            .arg("/link")
            .arg(format!("/out:{}", library_path.to_str().unwrap()));
    } else {
        #[cfg(not(windows))]
        command.arg("-fPIC");

View on GitHub (pinned to 079a789e8c)

Solutions

1. Run the build from an 'x64 Native Tools Command Prompt' (or vsdevcmd) so cl.exe, INCLUDE and LIB are set
2. Read the embedded Stderr - the actual cl diagnostic (C2xxx errors) tells you whether it is headers, arch, or language level
3. Install/repair 'Desktop development with C++' workload incl. Windows SDK in Visual Studio Build Tools
4. If a specific grammar's scanner needs newer C++, update Helix or override that grammar's source to a compatible revision

// Pre-flight on Windows: cl.exe must run and target the right arch
fn msvc_ready() -> bool {
    std::process::Command::new("cmd").args(["/C", "cl /nologo >nul 2>&1"]).status().map(|s| s.success()).unwrap_or(false)
}

// build_grammars returns Result; on failure print the embedded compiler
// stderr so the user sees the cl diagnostic instead of just the wrapper:
if let Err(e) = helix_loader::grammar::build_grammars() {
    eprintln!("{e:#}"); // anyhow alternate formatting shows Stdout/Stderr chains
}

When it happens

Trigger: 'hx --grammar build' on Windows where cl.exe runs but fails: C++14-incompatible scanner code, mismatched target architecture (x64 host tools vs 32-bit build), missing Windows SDK / include paths, or scanners needing newer C++ than /std:c++14.

Common situations: Building grammars outside a 'Developer Command Prompt/x64 Native Tools' environment so INCLUDE/LIB env vars are absent; VS Build Tools installed without the C++ workload or SDK; scanner.cc from a newer grammar release using C++17 constructs.

Related errors

• Directory {:?} is empty. Did you use 'hx --grammar fetch'?
• Git command failed. Stdout: {} Stderr: {}
• --grammar must be followed by either 'fetch' or 'build'
• Failed to parse snippet. Remaining input: {}
• Command not provided

AI-assisted analysis of helix-editor/helix@079a789e8c (2026-08-16). Data as JSON: /api/errors/09b379b0caf4796b. Report an issue: GitHub.