{} uses reserved table `[__baml_codegen]`; remove it because

Error message

{} uses reserved table `[__baml_codegen]`; remove it because `baml generate` owns generated-bytecode metadata.

What it means

When embedding the project's baml.toml into generated bytecode, `build_embedded_baml_toml` rejects any baml.toml that defines a `[__baml_codegen]` table, because `baml generate` reserves and owns that table for generated-bytecode metadata. User-authored configs must not use it.

Source

Thrown at baml_language/crates/baml_cli/src/generate.rs:595

            reporter.abandon();
            crate::reporter::print_error("no files generated (no supported generators found)");
            return Ok(crate::ExitCode::Other);
        }

        reporter.finish("Finished", format!("generated {total_files} file(s)"));
        Ok(crate::ExitCode::Success)
    }
}

fn build_embedded_baml_toml(project_root: &Path) -> Result<String> {
    let path = project_root.join("baml.toml");
    let content = std::fs::read_to_string(&path)
        .with_context(|| format!("failed to read {}", path.display()))?;
    let document = content
        .parse::<DocumentMut>()
        .with_context(|| format!("failed to parse {}", path.display()))?;
    if document.contains_key("__baml_codegen") {
        anyhow::bail!(
            "{} uses reserved table `[__baml_codegen]`; remove it because `baml generate` owns generated-bytecode metadata.",
            path.display()
        );
    }

    let mut embedded = content;
    if !embedded.ends_with('\n') {
        embedded.push('\n');
    }
    embedded.push_str(
        "\n[__baml_codegen]\nmetadata_version = 1\n\n[__baml_codegen.toolchain]\nversion = ",
    );
    embedded.push_str(&format!("{:?}", baml_version::CANONICAL_VERSION));
    embedded.push('\n');
    Ok(embedded)
}

/// Pseudo [`FileId`] for `baml.toml`. The manifest isn't a salsa source

View on GitHub (pinned to bd85ce9dee)

Solutions

Remove the `[__baml_codegen]` table (and its keys) from baml.toml
Re-run `baml generate` so the CLI regenerates its owned metadata
Keep the source baml.toml out of any flow that copies generated output over it

Example fix

// before (baml.toml)
[__baml_codegen]
version = 1

// after (baml.toml)
# table removed; baml generate owns [__baml_codegen]

Defensive patterns

Strategy: validation

Validate before calling

let doc = std::fs::read_to_string("baml.toml")?.parse::<toml_edit::DocumentMut>()?;
assert!(!doc.contains_key("__baml_codegen"), "remove reserved [__baml_codegen] table from source baml.toml");

Try / catch

match result {
    Err(e) if e.to_string().contains("__baml_codegen") => {
        eprintln!("Strip the reserved [__baml_codegen] table from baml.toml and regenerate.");
    }
    other => other?,
}

Prevention

Never check generated baml.toml output back into your source project
Add a lint/pre-commit check for the __baml_codegen key in source configs
Keep generated artifacts in ignored output directories

When it happens

Trigger: Running `baml generate` (or tests exercising embedded manifests) against a project whose baml.toml literally contains a `[__baml_codegen]` table, either hand-written or left over from a previous generation flow.

Common situations: A developer copied a generated baml.toml back into source control, or manually edited generated output and reintroduced the reserved table.

Related errors

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/809e6495960a9fcf. Report an issue: GitHub.