mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-19 01:24:05 +00:00
543 lines
19 KiB
Rust
543 lines
19 KiB
Rust
use reexport::*;
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use rustc::hir::*;
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use rustc::hir::intravisit::FnKind;
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use rustc::lint::*;
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use rustc::middle::const_val::ConstVal;
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use rustc::ty;
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use rustc_const_eval::ConstContext;
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use rustc_const_math::ConstFloat;
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use syntax::codemap::{Span, ExpnFormat};
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use utils::{get_item_name, get_parent_expr, implements_trait, in_macro, is_integer_literal, match_path, snippet,
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span_lint, span_lint_and_then, walk_ptrs_ty, last_path_segment, iter_input_pats, in_constant,
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match_trait_method, paths};
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use utils::sugg::Sugg;
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use syntax::ast::{LitKind, CRATE_NODE_ID};
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/// **What it does:** Checks for function arguments and let bindings denoted as `ref`.
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///
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/// **Why is this bad?** The `ref` declaration makes the function take an owned
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/// value, but turns the argument into a reference (which means that the value
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/// is destroyed when exiting the function). This adds not much value: either
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/// take a reference type, or take an owned value and create references in the
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/// body.
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///
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/// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The
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/// type of `x` is more obvious with the former.
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///
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/// **Known problems:** If the argument is dereferenced within the function,
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/// removing the `ref` will lead to errors. This can be fixed by removing the
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/// dereferences, e.g. changing `*x` to `x` within the function.
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///
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/// **Example:**
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/// ```rust
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/// fn foo(ref x: u8) -> bool { .. }
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/// ```
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declare_lint! {
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pub TOPLEVEL_REF_ARG,
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Warn,
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"an entire binding declared as `ref`, in a function argument or a `let` statement"
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}
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/// **What it does:** Checks for comparisons to NaN.
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///
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/// **Why is this bad?** NaN does not compare meaningfully to anything – not
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/// even itself – so those comparisons are simply wrong.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// x == NAN
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/// ```
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declare_lint! {
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pub CMP_NAN,
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Deny,
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"comparisons to NAN, which will always return false, probably not intended"
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}
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/// **What it does:** Checks for (in-)equality comparisons on floating-point
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/// values (apart from zero), except in functions called `*eq*` (which probably
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/// implement equality for a type involving floats).
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///
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/// **Why is this bad?** Floating point calculations are usually imprecise, so
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/// asking if two values are *exactly* equal is asking for trouble. For a good
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/// guide on what to do, see [the floating point
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/// guide](http://www.floating-point-gui.de/errors/comparison).
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// y == 1.23f64
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/// y != x // where both are floats
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/// ```
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declare_lint! {
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pub FLOAT_CMP,
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Warn,
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"using `==` or `!=` on float values instead of comparing difference with an epsilon"
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}
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/// **What it does:** Checks for conversions to owned values just for the sake
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/// of a comparison.
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///
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/// **Why is this bad?** The comparison can operate on a reference, so creating
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/// an owned value effectively throws it away directly afterwards, which is
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/// needlessly consuming code and heap space.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// x.to_owned() == y
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/// ```
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declare_lint! {
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pub CMP_OWNED,
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Warn,
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"creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`"
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}
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/// **What it does:** Checks for getting the remainder of a division by one.
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///
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/// **Why is this bad?** The result can only ever be zero. No one will write
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/// such code deliberately, unless trying to win an Underhanded Rust
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/// Contest. Even for that contest, it's probably a bad idea. Use something more
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/// underhanded.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// x % 1
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/// ```
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declare_lint! {
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pub MODULO_ONE,
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Warn,
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"taking a number modulo 1, which always returns 0"
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}
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/// **What it does:** Checks for patterns in the form `name @ _`.
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///
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/// **Why is this bad?** It's almost always more readable to just use direct bindings.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// match v {
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/// Some(x) => (),
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/// y @ _ => (), // easier written as `y`,
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/// }
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/// ```
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declare_lint! {
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pub REDUNDANT_PATTERN,
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Warn,
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"using `name @ _` in a pattern"
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}
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/// **What it does:** Checks for the use of bindings with a single leading underscore.
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///
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/// **Why is this bad?** A single leading underscore is usually used to indicate
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/// that a binding will not be used. Using such a binding breaks this
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/// expectation.
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///
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/// **Known problems:** The lint does not work properly with desugaring and
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/// macro, it has been allowed in the mean time.
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///
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/// **Example:**
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/// ```rust
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/// let _x = 0;
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/// let y = _x + 1; // Here we are using `_x`, even though it has a leading underscore.
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/// // We should rename `_x` to `x`
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/// ```
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declare_lint! {
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pub USED_UNDERSCORE_BINDING,
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Allow,
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"using a binding which is prefixed with an underscore"
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}
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/// **What it does:** Checks for the use of short circuit boolean conditions as a
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/// statement.
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///
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/// **Why is this bad?** Using a short circuit boolean condition as a statement may
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/// hide the fact that the second part is executed or not depending on the outcome of
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/// the first part.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// f() && g(); // We should write `if f() { g(); }`.
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/// ```
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declare_lint! {
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pub SHORT_CIRCUIT_STATEMENT,
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Warn,
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"using a short circuit boolean condition as a statement"
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}
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/// **What it does:** Catch casts from `0` to some pointer type
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///
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/// **Why is this bad?** This generally means `null` and is better expressed as
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/// {`std`, `core`}`::ptr::`{`null`, `null_mut`}.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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///
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/// ```rust
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/// 0 as *const u32
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/// ```
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declare_lint! {
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pub ZERO_PTR,
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Warn,
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"using 0 as *{const, mut} T"
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}
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#[derive(Copy, Clone)]
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pub struct Pass;
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array!(TOPLEVEL_REF_ARG,
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CMP_NAN,
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FLOAT_CMP,
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CMP_OWNED,
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MODULO_ONE,
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REDUNDANT_PATTERN,
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USED_UNDERSCORE_BINDING,
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SHORT_CIRCUIT_STATEMENT,
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ZERO_PTR)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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fn check_fn(
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&mut self,
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cx: &LateContext<'a, 'tcx>,
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k: FnKind<'tcx>,
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decl: &'tcx FnDecl,
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body: &'tcx Body,
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_: Span,
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_: NodeId
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) {
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if let FnKind::Closure(_) = k {
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// Does not apply to closures
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return;
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}
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for arg in iter_input_pats(decl, body) {
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if let PatKind::Binding(BindByRef(_), _, _, _) = arg.pat.node {
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span_lint(cx,
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TOPLEVEL_REF_ARG,
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arg.pat.span,
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"`ref` directly on a function argument is ignored. Consider using a reference type instead.");
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}
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}
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}
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fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, s: &'tcx Stmt) {
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if_let_chain! {[
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let StmtDecl(ref d, _) = s.node,
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let DeclLocal(ref l) = d.node,
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let PatKind::Binding(BindByRef(mt), _, i, None) = l.pat.node,
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let Some(ref init) = l.init
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], {
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let init = Sugg::hir(cx, init, "..");
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let (mutopt,initref) = if mt == Mutability::MutMutable {
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("mut ", init.mut_addr())
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} else {
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("", init.addr())
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};
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let tyopt = if let Some(ref ty) = l.ty {
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format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_"))
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} else {
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"".to_owned()
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};
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span_lint_and_then(cx,
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TOPLEVEL_REF_ARG,
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l.pat.span,
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"`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
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|db| {
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db.span_suggestion(s.span,
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"try",
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format!("let {name}{tyopt} = {initref};",
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name=snippet(cx, i.span, "_"),
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tyopt=tyopt,
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initref=initref));
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}
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);
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}};
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if_let_chain! {[
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let StmtSemi(ref expr, _) = s.node,
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let Expr_::ExprBinary(ref binop, ref a, ref b) = expr.node,
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binop.node == BiAnd || binop.node == BiOr,
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let Some(sugg) = Sugg::hir_opt(cx, a),
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], {
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span_lint_and_then(cx,
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SHORT_CIRCUIT_STATEMENT,
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s.span,
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"boolean short circuit operator in statement may be clearer using an explicit test",
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|db| {
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let sugg = if binop.node == BiOr { !sugg } else { sugg };
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db.span_suggestion(s.span, "replace it with",
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format!("if {} {{ {}; }}", sugg, &snippet(cx, b.span, "..")));
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});
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}};
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}
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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match expr.node {
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ExprCast(ref e, ref ty) => {
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check_cast(cx, expr.span, e, ty);
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return;
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},
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ExprBinary(ref cmp, ref left, ref right) => {
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let op = cmp.node;
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if op.is_comparison() {
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if let ExprPath(QPath::Resolved(_, ref path)) = left.node {
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check_nan(cx, path, expr);
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}
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if let ExprPath(QPath::Resolved(_, ref path)) = right.node {
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check_nan(cx, path, expr);
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}
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check_to_owned(cx, left, right);
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check_to_owned(cx, right, left);
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}
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if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
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if is_allowed(cx, left) || is_allowed(cx, right) {
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return;
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}
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if let Some(name) = get_item_name(cx, expr) {
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let name = name.as_str();
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if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_") ||
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name.ends_with("_eq") {
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return;
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}
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}
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span_lint_and_then(cx, FLOAT_CMP, expr.span, "strict comparison of f32 or f64", |db| {
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let lhs = Sugg::hir(cx, left, "..");
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let rhs = Sugg::hir(cx, right, "..");
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db.span_suggestion(expr.span,
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"consider comparing them within some error",
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format!("({}).abs() < error", lhs - rhs));
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db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available.");
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});
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} else if op == BiRem && is_integer_literal(right, 1) {
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span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
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}
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},
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_ => {},
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}
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if in_attributes_expansion(expr) {
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// Don't lint things expanded by #[derive(...)], etc
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return;
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}
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let binding = match expr.node {
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ExprPath(ref qpath) => {
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let binding = last_path_segment(qpath).name.as_str();
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if binding.starts_with('_') &&
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!binding.starts_with("__") &&
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binding != "_result" && // FIXME: #944
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is_used(cx, expr) &&
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// don't lint if the declaration is in a macro
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non_macro_local(cx, &cx.tables.qpath_def(qpath, expr.id)) {
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Some(binding)
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} else {
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None
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}
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},
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ExprField(_, spanned) => {
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let name = spanned.node.as_str();
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if name.starts_with('_') && !name.starts_with("__") {
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Some(name)
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} else {
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None
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}
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},
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_ => None,
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};
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if let Some(binding) = binding {
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span_lint(cx,
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USED_UNDERSCORE_BINDING,
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expr.span,
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&format!("used binding `{}` which is prefixed with an underscore. A leading \
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underscore signals that a binding will not be used.",
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binding));
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}
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}
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fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
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if let PatKind::Binding(_, _, ref ident, Some(ref right)) = pat.node {
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if right.node == PatKind::Wild {
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span_lint(cx,
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REDUNDANT_PATTERN,
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pat.span,
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&format!("the `{} @ _` pattern can be written as just `{}`", ident.node, ident.node));
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}
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}
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}
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}
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fn check_nan(cx: &LateContext, path: &Path, expr: &Expr) {
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if !in_constant(cx, expr.id) {
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path.segments.last().map(|seg| if seg.name == "NAN" {
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span_lint(cx,
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CMP_NAN,
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expr.span,
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"doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead");
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});
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}
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}
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fn is_allowed(cx: &LateContext, expr: &Expr) -> bool {
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let res = ConstContext::with_tables(cx.tcx, cx.tables).eval(expr);
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if let Ok(ConstVal::Float(val)) = res {
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use std::cmp::Ordering;
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match val {
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val @ ConstFloat::F32(_) => {
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let zero = ConstFloat::F32(0.0);
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let infinity = ConstFloat::F32(::std::f32::INFINITY);
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let neg_infinity = ConstFloat::F32(::std::f32::NEG_INFINITY);
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val.try_cmp(zero) == Ok(Ordering::Equal) || val.try_cmp(infinity) == Ok(Ordering::Equal) ||
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val.try_cmp(neg_infinity) == Ok(Ordering::Equal)
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},
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val @ ConstFloat::F64(_) => {
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let zero = ConstFloat::F64(0.0);
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let infinity = ConstFloat::F64(::std::f64::INFINITY);
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let neg_infinity = ConstFloat::F64(::std::f64::NEG_INFINITY);
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val.try_cmp(zero) == Ok(Ordering::Equal) || val.try_cmp(infinity) == Ok(Ordering::Equal) ||
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val.try_cmp(neg_infinity) == Ok(Ordering::Equal)
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},
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}
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} else {
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false
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}
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}
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fn is_float(cx: &LateContext, expr: &Expr) -> bool {
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matches!(walk_ptrs_ty(cx.tables.expr_ty(expr)).sty, ty::TyFloat(_))
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}
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fn check_to_owned(cx: &LateContext, expr: &Expr, other: &Expr) {
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let (arg_ty, snip) = match expr.node {
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ExprMethodCall(.., ref args) if args.len() == 1 => {
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if match_trait_method(cx, expr, &paths::TO_STRING) || match_trait_method(cx, expr, &paths::TO_OWNED) {
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(cx.tables.expr_ty_adjusted(&args[0]), snippet(cx, args[0].span, ".."))
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} else {
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return;
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}
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},
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ExprCall(ref path, ref v) if v.len() == 1 => {
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if let ExprPath(ref path) = path.node {
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if match_path(path, &["String", "from_str"]) || match_path(path, &["String", "from"]) {
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(cx.tables.expr_ty_adjusted(&v[0]), snippet(cx, v[0].span, ".."))
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} else {
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return;
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}
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} else {
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return;
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}
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},
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_ => return,
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};
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let other_ty = cx.tables.expr_ty_adjusted(other);
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let partial_eq_trait_id = match cx.tcx.lang_items.eq_trait() {
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Some(id) => id,
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None => return,
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};
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// *arg impls PartialEq<other>
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if !arg_ty
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.builtin_deref(true, ty::LvaluePreference::NoPreference)
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.map_or(false, |tam| implements_trait(cx, tam.ty, partial_eq_trait_id, &[other_ty]))
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// arg impls PartialEq<*other>
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&& !other_ty
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.builtin_deref(true, ty::LvaluePreference::NoPreference)
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.map_or(false, |tam| implements_trait(cx, arg_ty, partial_eq_trait_id, &[tam.ty]))
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// arg impls PartialEq<other>
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&& !implements_trait(cx, arg_ty, partial_eq_trait_id, &[other_ty]) {
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return;
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}
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span_lint_and_then(cx,
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CMP_OWNED,
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expr.span,
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"this creates an owned instance just for comparison",
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|db| {
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// this is as good as our recursion check can get, we can't prove that the current function is
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// called by
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// PartialEq::eq, but we can at least ensure that this code is not part of it
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let parent_fn = cx.tcx.hir.get_parent(expr.id);
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let parent_impl = cx.tcx.hir.get_parent(parent_fn);
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if parent_impl != CRATE_NODE_ID {
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if let map::NodeItem(item) = cx.tcx.hir.get(parent_impl) {
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if let ItemImpl(.., Some(ref trait_ref), _, _) = item.node {
|
||
if trait_ref.path.def.def_id() == partial_eq_trait_id {
|
||
// we are implementing PartialEq, don't suggest not doing `to_owned`, otherwise we go into
|
||
// recursion
|
||
db.span_label(expr.span, "try calling implementing the comparison without allocating");
|
||
return;
|
||
}
|
||
}
|
||
}
|
||
}
|
||
db.span_suggestion(expr.span, "try", snip.to_string());
|
||
});
|
||
}
|
||
|
||
/// Heuristic to see if an expression is used. Should be compatible with `unused_variables`'s idea
|
||
/// of what it means for an expression to be "used".
|
||
fn is_used(cx: &LateContext, expr: &Expr) -> bool {
|
||
if let Some(parent) = get_parent_expr(cx, expr) {
|
||
match parent.node {
|
||
ExprAssign(_, ref rhs) |
|
||
ExprAssignOp(_, _, ref rhs) => **rhs == *expr,
|
||
_ => is_used(cx, parent),
|
||
}
|
||
} else {
|
||
true
|
||
}
|
||
}
|
||
|
||
/// Test whether an expression is in a macro expansion (e.g. something generated by
|
||
/// `#[derive(...)`] or the like).
|
||
fn in_attributes_expansion(expr: &Expr) -> bool {
|
||
expr.span.ctxt.outer().expn_info().map_or(false, |info| matches!(info.callee.format, ExpnFormat::MacroAttribute(_)))
|
||
}
|
||
|
||
/// Test whether `def` is a variable defined outside a macro.
|
||
fn non_macro_local(cx: &LateContext, def: &def::Def) -> bool {
|
||
match *def {
|
||
def::Def::Local(def_id) |
|
||
def::Def::Upvar(def_id, _, _) => {
|
||
let id = cx.tcx
|
||
.hir
|
||
.as_local_node_id(def_id)
|
||
.expect("local variables should be found in the same crate");
|
||
!in_macro(cx.tcx.hir.span(id))
|
||
},
|
||
_ => false,
|
||
}
|
||
}
|
||
|
||
fn check_cast(cx: &LateContext, span: Span, e: &Expr, ty: &Ty) {
|
||
if_let_chain! {[
|
||
let TyPtr(MutTy { mutbl, .. }) = ty.node,
|
||
let ExprLit(ref lit) = e.node,
|
||
let LitKind::Int(value, ..) = lit.node,
|
||
value == 0,
|
||
!in_constant(cx, e.id)
|
||
], {
|
||
let msg = match mutbl {
|
||
Mutability::MutMutable => "`0 as *mut _` detected. Consider using `ptr::null_mut()`",
|
||
Mutability::MutImmutable => "`0 as *const _` detected. Consider using `ptr::null()`",
|
||
};
|
||
span_lint(cx, ZERO_PTR, span, msg);
|
||
}}
|
||
}
|