rust-lang/cargo · error · anyhow::Error

`lints.{tool}.{name}` is not valid lint name; try `lints.{pr

Error message

`lints.{tool}.{name}` is not valid lint name; try `lints.{prefix}.{suffix}`

What it means

Thrown during lint-table validation at src/workspace/parser/mod.rs:2727. If a lint name contains `::` and its first segment equals the tool name (e.g. `[lints.rust] rust::foo = ...` → prefix "rust" == tool "rust"), cargo treats it as a redundant/misplaced qualifier and suggests dropping the prefix by rewriting it as `lints.{prefix}.{suffix}` (i.e. `lints.rust.foo`).

Source

Thrown at src/workspace/parser/mod.rs:2727

        for (name, config) in lints {
            let normalized = name.replace('-', "_");
            if name.contains('-') {
                warnings.push(format!(
                    "`lints.{tool}.{name}` is deprecated in favor of \
                     `lints.{tool}.{normalized}` and will not work in a \
                     future edition"
                ));
            }
            if let Some(existing) = seen_normalized.get(&normalized) {
                warnings.push(format!(
                    "duplicate lint `{existing}` in `[lints.{tool}]`, \
                     conflicts with `{name}` and will not work in a future edition"
                ));
            }
            seen_normalized.insert(normalized.clone(), name.to_string());
            if let Some((prefix, suffix)) = name.split_once("::") {
                if tool == prefix {
                    anyhow::bail!(
                        "`lints.{tool}.{name}` is not valid lint name; try `lints.{prefix}.{suffix}`"
                    )
                } else if tool == "rust" && supported.contains(&prefix) {
                    anyhow::bail!(
                        "`lints.{tool}.{name}` is not valid lint name; try `lints.{prefix}.{suffix}`"
                    )
                } else {
                    anyhow::bail!("`lints.{tool}.{name}` is not a valid lint name")
                }
            } else if let Some(config) = config.config() {
                for config_name in config.keys() {
                    // manually report unused manifest key warning since we collect all the "extra"
                    // keys and values inside the config table
                    let expected = EXPECTED_LINT_CONFIG.contains(&(tool, name, config_name));
                    if !expected {
                        let message =
                            format!("unused manifest key: `lints.{tool}.{name}.{config_name}`");
                        warnings.push(message);

View on GitHub (pinned to 0e07a15537)

Solutions

1. Remove the redundant `tool::` prefix: under `[lints.rust]` write `foo = "warn"` instead of `rust::foo = "warn"`.
2. Use the bare lint name that matches the table's tool.

Example fix

# before
[lints.rust]
rust::doc_markdown = "warn"
# after
[lints.rust]
doc_markdown = "warn"

for (name, _) in lints_for_tool {
    if let Some((prefix, _suffix)) = name.split_once("::") {
        if prefix == tool {
            return Err(format!("lint {name} redundantly repeats tool {tool}"));
        }
    }
}

When it happens

Trigger: Writing `[lints.rust] rust::doc_markdown = "warn"` or `[lints.cargo] cargo::... ` — the lint key redundantly repeats the tool as a `::` prefix.

Common situations: Copy-pasting the fully-qualified rustc lint name (`rust::xxx`) directly into the `[lints.rust]` table; tooling that emits group-qualified names.

Related errors

• `lints.{tool}.{name}` is not a valid lint name
• the crate `{}` depends on crate `{}` multiple times with dif
• Use of `default_features` in `{key}` is unsupported, please
• cannot override `workspace.lints` in `lints`, either remove
• `{old_path}` is unsupported as of the 2024 edition; instead

AI-assisted analysis of rust-lang/cargo@0e07a15537 (2026-08-06). Data as JSON: /data/errors/1a153f1230c7cb09.json. Report an issue: GitHub.