Validation

The parser runs semantic validation after converting the YAML document to the domain model. Validation checks are named V-001 through V-008, following the Teckel Specification.

Module: crates/teckel-parser/src/validate.rs

Validation rules

V-001: Reference integrity

Every asset reference used in from, left, right, sources, or views fields must point to a defined asset in the context.

[E-REF-001] asset "filtered" references undefined asset "emplyees" (did you mean "employees"?)

The validator includes a Levenshtein distance-based suggestion when a similar asset name exists (distance <= 3).

V-002: No cycles

The asset dependency graph must be a directed acyclic graph (DAG). The validator builds a directed graph using petgraph and attempts a topological sort. If the sort fails, a cycle exists.

[E-CYCLE-001] circular dependency detected in the pipeline DAG

V-003: Output reference validation

Output names must reference assets from the input or transformation sections. An output cannot reference another output.

[E-REF-001] output "result" references undefined asset

V-005: Non-empty lists

Fields typed as NonEmptyList in the spec must contain at least one element. The parser checks that input and output arrays are non-empty.

[E-LIST-001] "input" must contain at least one element
[E-LIST-001] "output" must contain at least one element

V-007: AssetRef format

All asset names must match the pattern ^[a-zA-Z][a-zA-Z0-9_-]{0,127}$. Names must start with a letter and contain only alphanumeric characters, underscores, and hyphens.

[E-NAME-002] invalid AssetRef "123_bad" -- must start with a letter

V-008: Version field

The version field must be present and set to "2.0" or "3.0". This check runs before the full validation pass.

[E-VERSION-001] unsupported version "1.0", expected "2.0" or "3.0"

Expression validation (optional)

When ParseOptions::validate_expressions is set to true, the parser additionally validates all expression and condition strings by parsing them with the built-in expression parser.

let options = ParseOptions {
    variables: &vars,
    secrets_provider: &EnvSecretsProvider,
    validate_expressions: true,  // Enable expression validation
};

let pipeline = parse_with_options(yaml, &options)?;

Invalid expressions produce error E-EXPR-001:

[E-EXPR-001] invalid expression in "computed": unexpected token ">>" (expression: "col1 >> 2")

Error collection

The validator collects all errors rather than stopping at the first one. If multiple validation rules fail, the result is a TeckelError::Validation containing all individual errors:

pub enum TeckelError {
    // ...
    Validation {
        count: usize,
        errors: Vec<TeckelError>,
    },
}

This lets callers report all issues in a single pass rather than requiring iterative fix-and-retry cycles.

Validation order

The checks run in this order:

1. V-008 -- Version (runs before the main validation pass)
2. V-007 -- AssetRef format
3. V-005 -- Non-empty lists
4. V-001 -- Reference integrity
5. V-002 -- No cycles
6. V-003 -- Output references