vectordotdev/vector · error

argument must be a string

Error message

argument must be a string

What it means

find_vector_metrics' helper unwraps its key with key.as_str().expect("argument must be a string") (lib/vector-vrl/metrics/src/find_vector_metrics.rs). The key parameter is declared required BYTES in the function's parameter list, and the VRL compiler type-checks call sites, so this panic indicates the runtime value violated a compile-time guarantee (internal invariant) rather than a user scripting mistake.

Source

Thrown at lib/vector-vrl/metrics/src/find_vector_metrics.rs:16

use std::{collections::BTreeMap, sync::LazyLock};
use vector_vrl_category::Category;
use vrl::prelude::expression::Expr;

use vrl::prelude::*;

use crate::common::{
    metric_into_vrl, metrics_vrl_typedef, resolve_tags, validate_tags, Error, MetricsStorage,
};

fn find_metrics(
    metrics_storage: &MetricsStorage,
    key: Value,
    tags: BTreeMap<String, String>,
) -> Result<Value, ExpressionError> {
    let key_str = key.as_str().expect("argument must be a string");
    Ok(Value::Array(
        metrics_storage
            .find_metrics(&key_str, tags)
            .iter()
            .map(metric_into_vrl)
            .collect(),
    ))
}

static DEFAULT_TAGS: LazyLock<Value> = LazyLock::new(|| Value::Object(BTreeMap::new()));

static PARAMETERS: LazyLock<Vec<Parameter>> = LazyLock::new(|| {
    vec![
        Parameter::required("key", kind::BYTES, "The metric name to search."),
        Parameter::optional(
            "tags",
            kind::OBJECT,
            "Tags to filter the results on. Values in this object support wildcards ('*') to match on parts of the tag value.",

View on GitHub (pinned to 3708c39b12)

Solutions

1. Align vector-vrl crates to a single Vector release
2. Use string literals or to_string! for the key in VRL programs
3. Invoke functions only through compiled programs in embedding code
4. Report compiler-invariant breaks with a minimal VRL program upstream

Example fix

# before (vrl)
find_vector_metrics(key)   # key: any

# after (vrl)
find_vector_metrics(to_string!(key))

# Statically-typed key argument
find_vector_metrics(to_string!(key))

fn is_bytes(v: &vrl::value::Value) -> bool {
    matches!(v, vrl::value::Value::Bytes(_))
}

When it happens

Trigger: The compiled function executing with a non-bytes key Value — normally impossible because find_vector_metrics(42) is rejected during VRL compilation; triggered by compiler regressions, mixed vector-vrl crate versions, or code invoking the helper directly (unit tests, embeddings).

Common situations: VRL compiler development and fuzzing; custom builds with partially upgraded vector-vrl-* crates; direct helper calls in internal tests.

Related errors

• argument must be a string
• argument must be a string
• argument must be a string
• argument must be a string
• key must be a string

AI-assisted analysis of vectordotdev/vector@3708c39b12 (2026-08-20). Data as JSON: /api/errors/25625d99c3e03eb4. Report an issue: GitHub.