BoundaryML/baml · error · anyhow::Error

Field type uses unresolvable local identifier {}

Error message

Field type uses unresolvable local identifier {}

What it means

When resolving a field's type in the IR, a local identifier used as a type must resolve to a known walker/walker-resolved type. If the identifier (e.g. a field type name) cannot be resolved in scope, BAML returns this error. It indicates a type reference in a class/field definition that points to nothing in the schema.

Source

Thrown at engine/baml-lib/baml-core/src/ir/repr.rs:1950

                            _ => base_type,
                        }
                    }
                    Some(TypeWalker::TypeAlias(alias_walker)) => {
                        if db.is_recursive_type_alias(&alias_walker.id) {
                            let resolved = alias_walker.resolved();
                            // TODO: use resolved in some way
                            TypeIR::RecursiveTypeAlias {
                                name: alias_walker.name().to_string(),
                                mode: StreamingMode::Streaming,
                                meta: Default::default(),
                            }
                        } else {
                            alias_walker.resolved().to_owned().repr(db)?
                        }
                    }

                    None => {
                        return Err(anyhow!(
                            "Field type uses unresolvable local identifier {}",
                            idn
                        ))
                    }
                },
                arity,
            ),
            ast::FieldType::List(arity, ft, dims, ..) => {
                // NB: potential bug: this hands back a 1D list when dims == 0
                let mut repr = TypeIR::List(Box::new(ft.repr(db)?), Default::default());

                for _ in 1u32..*dims {
                    repr = TypeIR::list(repr);
                }

                if arity.is_optional() {
                    repr = TypeIR::optional(repr);
                }

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Check the identifier in the message against your defined classes/enums/type aliases.
2. Fix casing and spelling — BAML type names are case-sensitive.
3. Ensure the file defining the referenced type is included in the generator's source globs.
4. Run baml CLI generate to list all unresolved type references at once.

Example fix

// before
class Order {
  buyer Usr
}
// after
class Order {
  buyer User
}

# verify class field type names resolve to defined types
import re
defined = set(re.findall(r'^\s*(?:class|enum)\s+(\w+)', src, re.M))
defined |= set(re.findall(r'^\s*type\s+(\w+)\s*=', src, re.M))
defined |= {"string", "int", "float", "bool", "map", "string[]"}
for cls in re.finditer(r'class\s+\w+\s*\{(.*?)\}', src, re.S):
    for ftype in re.findall(r'^\s*\w+\s+([A-Z]\w*)', cls.group(1), re.M):
        if ftype not in defined:
            print(f"unresolved field type: {ftype}")

match ast_field_type.repr(db) {
    Ok(t) => t,
    Err(e) if e.to_string().contains("unresolvable local identifier") => {
        eprintln!("define or correctly spell the referenced type before generating");
        return Err(e);
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: repr(db) on a field type containing an identifier (idn) with no matching resolution in the local scope — i.e. a class field typed with a name that is not a defined class, enum, alias, or primitive in the BAML schema.

Common situations: Typo in a class field's type name; referencing a class/enum defined in another .baml file not loaded; deleting/renaming a type while fields still reference it; case-sensitivity mistakes (user vs User).

Related errors

• Type alias not found: {name}
• Expression functions must have a return type
• Expression functions must have return type.
• Type mismatch: {message}
• Schema inconsistency: {message}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/325656b8c1c9535a. Report an issue: GitHub.