clippy::disallowed_types: Denies the configured types in clippy.toml. Note: Even though this lint is warn-by-default, it will only trigger if types are defined in the clippy.toml file

use std::collections::BTreeMap;
// or its use
let x = std::collections::BTreeMap::new();

// A similar type that is allowed by the config
use std::collections::HashMap;

#[allow(clippy::disallowed_types)]
fn my_function() { /* ... */ }

[lints.clippy]
disallowed_types = "allow"

cargo clippy -- -A clippy::disallowed-types

Clippy's own documentation

What it does

Denies the configured types in clippy.toml.

Note: Even though this lint is warn-by-default, it will only trigger if types are defined in the clippy.toml file.

Why is this bad?

Some types are undesirable in certain contexts.

Example:

An example clippy.toml configuration:

disallowed-types = [
    # Can use a string as the path of the disallowed type.
    "std::collections::BTreeMap",
    # Can also use an inline table with a `path` key.
    { path = "std::net::TcpListener" },
    # When using an inline table, can add a `reason` for why the type
    # is disallowed.
    { path = "std::net::Ipv4Addr", reason = "no IPv4 allowed" },
    # Can also add a `replacement` that will be offered as a suggestion.
    { path = "std::sync::Mutex", reason = "prefer faster & simpler non-poisonable mutex", replacement = "parking_lot::Mutex" },
    # This would normally error if the path is incorrect, but with `allow-invalid` = `true`,
    # it will be silently ignored
    { path = "std::invalid::Type", reason = "use alternative instead", allow-invalid = true }
]

use std::collections::BTreeMap;
// or its use
let x = std::collections::BTreeMap::new();

Use instead:

// A similar type that is allowed by the config
use std::collections::HashMap;

Past names

• disallowed_type

Configuration

• disallowed-types: The list of disallowed types, written as fully qualified paths.

Fields:

• path (required): the fully qualified path to the type that should be disallowed

• reason (optional): explanation why this type is disallowed

• replacement (optional): suggested alternative type

• allow-invalid (optional, false by default): when set to true, it will ignore this entry if the path doesn’t exist, instead of emitting an error

  (default: [])

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

Related lints

• needless_returnunneeded `return` statement
• new_without_defaultChecks for public types with a pub fn new() -> Self method and no implementation of Default
• len_zeroChecks for getting the length of something via .len() just to compare to zero, and suggests using .is_empty() where applicable
• disallowed_macrosDenies the configured macros in clippy.toml Note: Even though this lint is warn-by-default, it will only trigger if macros are defined in the clippy.toml file
• disallowed_methodsDenies the configured methods and functions in clippy.toml Note: Even though this lint is warn-by-default, it will only trigger if methods are defined in the clippy.toml file
• disallowed_namesuse of a disallowed/placeholder name `foo`
• doc_lazy_continuationdoc quote line without `>` marker
• doc_overindented_list_itemsDetects overindented list items in doc comments where the continuation lines are indented more than necessary
• double_must_usethis function has a `#[must_use]` attribute with no message, but returns a type already considered as `#[must_use]`

All 847 Clippy lints · Rust compiler errors · Cargo.toml checker