is a file, not a directory (expected a directory containing…

Error message

{dir:#?} is a file, not a directory (expected a directory containing BAML files)

What it means

baml_src_files() expects the given path to be a directory containing .baml files. After confirming the path exists, it checks that the path is not a regular file; pointing it at a file raises this error. It guards against passing something like a single .baml file or a config file where a directory is expected.

Solutions

Pass the directory (e.g. ./baml_src), not a file inside it
Remove any trailing filename from the configured baml_src path in your CLI args or runtime config
Point editor extension settings at the baml_src folder, not an individual .baml file

Example fix

// before
baml_src_files(&PathBuf::from("baml_src/main.baml"))?

// after
baml_src_files(&PathBuf::from("baml_src"))?

Defensive patterns

Strategy: validation

Validate before calling

import fs from 'fs';
const p = './baml_src';
if (fs.existsSync(p) && !fs.statSync(p).isDirectory()) throw new Error(`${p} must be the baml_src directory, not a file`);

Type guard

function isDirectory(p: string): boolean {
  try { return fs.statSync(p).isDirectory(); } catch { return false; }
}

Try / catch

try {
  bamlSrcFiles(dir);
} catch (e) {
  if (/is a file, not a directory/i.test(e.message)) {
    console.error(`Pass the folder (e.g. ./baml_src) instead of a file: ${dir}`);
  }
  throw e;
}

Prevention

Point configs and editor settings at the baml_src folder, never an individual .baml file
Strip trailing filenames from path variables before calling generation APIs
Keep a single source of truth for the baml_src path in your build scripts

When it happens

Trigger: Calling baml_src_files with a PathBuf such as "baml_src/main.baml" or any other file path instead of the directory (e.g. "./baml_src").

Common situations: Configuring the editor extension or runtime with the path to a single .baml file instead of the source folder; accidentally passing a config file (baml.json) as the source path; shell scripts that append a filename to the source directory.

Related errors

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/917df0c56083ae5c. Report an issue: GitHub.

Appendix: source

Thrown at engine/baml-runtime/src/lib.rs:2247

        &self,
        function_name: &str,
        test_name: &str,
    ) -> Result<Option<TypeBuilder>> {
        self.get_test_type_builder_impl(function_name, test_name)
    }
}

#[cfg(not(target_arch = "wasm32"))]
pub fn baml_src_files(dir: &std::path::PathBuf) -> Result<Vec<PathBuf>> {
    static VALID_EXTENSIONS: [&str; 1] = ["baml"];

    log::trace!("Reading files from {:#}", dir.to_string_lossy());

    if !dir.exists() {
        anyhow::bail!("{dir:#?} does not exist (expected a directory containing BAML files)",);
    }
    if dir.is_file() {
        return Err(anyhow::anyhow!(
            "{dir:#?} is a file, not a directory (expected a directory containing BAML files)",
        ));
    }
    if !dir.is_dir() {
        return Err(anyhow::anyhow!(
            "{dir:#?} is not a directory (expected a directory containing BAML files)",
        ));
    }

    let src_files = walkdir::WalkDir::new(dir)
        .into_iter()
        .filter_map(|e| match e {
            Ok(e) => Some(e),
            Err(e) => {
                log::error!("Error while reading files from {dir:#?}: {e}");
                None
            }
        })

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