444 lines
15 KiB
Rust
444 lines
15 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::EvalHint::ExprTypeChecked;
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use rustc_const_eval::eval_const_expr_partial;
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use rustc_const_math::ConstFloat;
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use syntax::codemap::{Span, Spanned, 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};
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use utils::sugg::Sugg;
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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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#[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, CMP_NAN, FLOAT_CMP, CMP_OWNED, MODULO_ONE, REDUNDANT_PATTERN,
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USED_UNDERSCORE_BINDING)
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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(&mut self, cx: &LateContext<'a, 'tcx>, k: FnKind<'tcx>, decl: &'tcx FnDecl, _: &'tcx Expr, _: Span,
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_: NodeId) {
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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 &decl.inputs {
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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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}
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
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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.span);
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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.span);
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}
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check_to_owned(cx, left, right, true, cmp.span);
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check_to_owned(cx, right, left, false, cmp.span)
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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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if in_attributes_expansion(cx, 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.tcx.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.", 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 `{}`",
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ident.node,
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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, span: Span) {
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path.segments.last().map(|seg| {
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if &*seg.name.as_str() == "NAN" {
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span_lint(cx,
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CMP_NAN,
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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 = eval_const_expr_partial(cx.tcx, expr, ExprTypeChecked, None);
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if let Ok(ConstVal::Float(val)) = res {
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use std::cmp::Ordering;
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let zero = ConstFloat::FInfer {
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f32: 0.0,
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f64: 0.0,
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};
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let infinity = ConstFloat::FInfer {
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f32: ::std::f32::INFINITY,
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f64: ::std::f64::INFINITY,
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};
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let neg_infinity = ConstFloat::FInfer {
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f32: ::std::f32::NEG_INFINITY,
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f64: ::std::f64::NEG_INFINITY,
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};
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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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} 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.tcx.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, left: bool, op: Span) {
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let (arg_ty, snip) = match expr.node {
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ExprMethodCall(Spanned { node: ref name, .. }, _, ref args) if args.len() == 1 => {
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let name = &*name.as_str();
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if name == "to_string" || name == "to_owned" && is_str_arg(cx, args) {
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(cx.tcx.tables().expr_ty(&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.tcx.tables().expr_ty(&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.tcx.tables().expr_ty(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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if !implements_trait(cx, arg_ty, partial_eq_trait_id, vec![other_ty]) {
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return;
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}
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if left {
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span_lint(cx,
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CMP_OWNED,
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expr.span,
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&format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
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compare without allocation",
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snip,
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snippet(cx, op, "=="),
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snippet(cx, other.span, "..")));
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} else {
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span_lint(cx,
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CMP_OWNED,
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expr.span,
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&format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
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compare without allocation",
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snippet(cx, other.span, ".."),
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snippet(cx, op, "=="),
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snip));
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}
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}
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fn is_str_arg(cx: &LateContext, args: &[Expr]) -> bool {
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args.len() == 1 && matches!(walk_ptrs_ty(cx.tcx.tables().expr_ty(&args[0])).sty, ty::TyStr)
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}
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/// Heuristic to see if an expression is used. Should be compatible with `unused_variables`'s idea
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/// of what it means for an expression to be "used".
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fn is_used(cx: &LateContext, expr: &Expr) -> bool {
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if let Some(parent) = get_parent_expr(cx, expr) {
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match parent.node {
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ExprAssign(_, ref rhs) |
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ExprAssignOp(_, _, ref rhs) => **rhs == *expr,
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_ => is_used(cx, parent),
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}
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} else {
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true
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}
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}
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/// Test whether an expression is in a macro expansion (e.g. something generated by
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/// `#[derive(...)`] or the like).
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fn in_attributes_expansion(cx: &LateContext, expr: &Expr) -> bool {
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cx.sess().codemap().with_expn_info(expr.span.expn_id, |info_opt| {
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info_opt.map_or(false, |info| matches!(info.callee.format, ExpnFormat::MacroAttribute(_)))
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})
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}
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/// Test whether `def` is a variable defined outside a macro.
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fn non_macro_local(cx: &LateContext, def: &def::Def) -> bool {
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match *def {
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def::Def::Local(id) |
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def::Def::Upvar(id, _, _) => {
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if let Some(span) = cx.tcx.map.span_if_local(id) {
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!in_macro(cx, span)
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} else {
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true
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}
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},
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_ => false,
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}
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}
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