vectordotdev/vector · critical

not implemented

Error message

not implemented

What it means

When Lua code builds a metric tag value set (a tag that can hold multiple values), the mlua `FromLua` impl for `TagValueSet` iterates the Lua table's sequence values and panics via `unimplemented!()` if any element fails to convert into a String. Only strings (and nil for the bare tag) are handled; numbers, booleans, or nested tables in the tag table hit the panic. This fires inside the Lua transform's `metric.*` API, e.g. `event.metric.tag.set_x({ ... })`.

Solutions

1. Convert every element to a string in the Lua script before passing the table: `event.metric.tag.set_tags({ "a", tostring(n) })`.
2. Keep tag tables homogeneous sequences of strings only — no numbers, booleans, nil holes, or mixed keys.
3. Prefer the VRL `remap` transform for tag manipulation; its type checking rejects non-string tags at compile time of the program.

Example fix

-- before (panics on the number)
event.metric.tag.set_tags({ "env", 42 })

-- after
event.metric.tag.set_tags({ "env", tostring(42) })

-- Lua: build the tag table defensively
local tags = {}
for i, v in ipairs(raw_tags) do
  if type(v) == "string" then tags[#tags+1] = v end
end
event.metric.tag.set_tags(tags)

-- Lua guard: every element must be a string
local ok = true
for i, v in ipairs(raw_tags) do
  if type(v) ~= "string" then ok = false end
end

When it happens

Trigger: Calling a metric tag setter from a `lua` transform with a table containing non-string entries, e.g. `event.metric.tag.set_tags({ "a", 1, true })` — the integer/boolean fails `String` conversion and the `Err(_)` arm panics. Passing a mixed or non-sequence table also ends up here.

Common situations: Porting Lua scripts that build tag lists from numeric data without `tostring`; config authors copying examples from Graylog/Lua docs that allow heterogeneous arrays; version upgrades where the metric Lua API changed to multi-valued tags.

Related errors

• argument must be a string
• argument must be a string
• argument must be a string
• invalid timestamp
• a record with a next ID must have an event count

AI-assisted analysis of vectordotdev/vector@3708c39b12 (2026-08-20). Data as JSON: /api/errors/2b4b5c38b1c896ca. Report an issue: GitHub.

Appendix: source

Thrown at lib/vector-core/src/event/lua/metric.rs:87

                to: String::from("StatisticKind"),
                message: Some(
                    "Statistic kind should be either \"summary\" or \"histogram\"".to_string(),
                ),
            }),
        }
    }
}

impl FromLua for TagValueSet {
    fn from_lua(value: LuaValue, _: &Lua) -> LuaResult<Self> {
        match value {
            LuaValue::Nil => Ok(Self::Single(TagValue::Bare)),
            LuaValue::Table(table) => {
                let mut string_values: Vec<String> = vec![];
                for value in table.sequence_values() {
                    match value {
                        Ok(value) => string_values.push(value),
                        Err(_) => unimplemented!(),
                    }
                }
                Ok(Self::from(string_values))
            }
            LuaValue::String(x) => Ok(Self::from([x.to_string_lossy().clone()])),
            _ => Err(mlua::Error::FromLuaConversionError {
                from: value.type_name(),
                to: String::from("metric tag value"),
                message: None,
            }),
        }
    }
}

impl FromLua for MetricTags {
    fn from_lua(value: LuaValue, lua: &Lua) -> LuaResult<Self> {
        Ok(Self(BTreeMap::from_lua(value, lua)?))
    }

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