Clippy lints / Pedantic
Clippy lint · Pedantic · checked with Clippy 0.1.99
clippy::invalid_upcast_comparisons: because of the numeric bounds on `x` prior to casting, this expression is always false
What it meansChecks for comparisons where the relation is always either true or false, but where one side has been upcast so that the comparison is necessary. Only integer types are checked. It is in the pedantic group and off by default.
What you see
warning: because of the numeric bounds on `x` prior to casting, this expression is always false --> main.rs:4:1 | 4 | (x as u32) > 300; | ^^^^^^^^^^^^^^^^ | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#invalid_upcast_comparisons = note: `-W clippy::invalid-upcast-comparisons` implied by `-W clippy::pedantic`
Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.
Does it matter?
An expression like let x : u8 = ...; (x as u32) > 300 will mistakenly imply that it is possible for x to be outside the range of u8.
Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.
How to fix it
Clippy does not fix this one automatically. Change the code by hand:
Flagged
let x: u8 = 1;
(x as u32) > 300;
Turn it off, or on
It is off by default. To use it, set it to warn or deny:
Whole crate (Cargo.toml)
[lints.clippy]
invalid_upcast_comparisons = "warn"In code
#![warn(clippy::invalid_upcast_comparisons)]One run
cargo clippy -- -W clippy::invalid-upcast-comparisonsThe [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.
Clippy's own documentation
What it does
Checks for comparisons where the relation is always either true or false, but where one side has been upcast so that the comparison is necessary. Only integer types are checked.
Why is this bad?
An expression like let x : u8 = ...; (x as u32) > 300
will mistakenly imply that it is possible for x to be outside the range of
u8.
Example
let x: u8 = 1;
(x as u32) > 300;
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- too_many_linesChecks for functions with a large amount of lines
- missing_errors_docChecks the doc comments of publicly visible functions that return a Result type and warns if there is no # Errors section
- must_use_candidateChecks for public functions that have no #[must_use] attribute, but return something not already marked must-use, have no mutable arg and mutate no statics
- inefficient_to_stringChecks for usage of .to_string() on an &&T where T implements ToString directly (like &&str or &&String)
- inline_alwaysChecks for items annotated with #[inline(always)], unless the annotated function is empty or simply panics
- into_iter_without_iterThis is the opposite of the iter_without_into_iter lint. It looks for IntoIterator for (&|&mut) Type implementations without an inherent iter or iter_mut method on the type or on any of the types in its Deref chain
- ip_constanthand-coded well-known IP address
- items_after_statementsadding items after statements is confusing, since items exist from the start of the scope
- iter_filter_is_ok`filter` for `is_ok` on iterator over `Result`s
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
Up next
Related lintclippy::too_many_linesChecks for functions with a large amount of linesRead it next →Did this answer your question?