rust/clippy_lints/src/misc.rs
2018-05-17 21:12:06 +02:00

588 lines
20 KiB
Rust
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

use reexport::*;
use rustc::hir::*;
use rustc::hir::intravisit::FnKind;
use rustc::lint::*;
use rustc::ty;
use syntax::codemap::{ExpnFormat, Span};
use utils::{get_item_name, get_parent_expr, implements_trait, in_constant, in_macro, is_integer_literal,
iter_input_pats, last_path_segment, match_qpath, match_trait_method, paths, snippet, span_lint,
span_lint_and_then, walk_ptrs_ty};
use utils::sugg::Sugg;
use syntax::ast::{LitKind, CRATE_NODE_ID};
use consts::{constant, Constant};
/// **What it does:** Checks for function arguments and let bindings denoted as
/// `ref`.
///
/// **Why is this bad?** The `ref` declaration makes the function take an owned
/// value, but turns the argument into a reference (which means that the value
/// is destroyed when exiting the function). This adds not much value: either
/// take a reference type, or take an owned value and create references in the
/// body.
///
/// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The
/// type of `x` is more obvious with the former.
///
/// **Known problems:** If the argument is dereferenced within the function,
/// removing the `ref` will lead to errors. This can be fixed by removing the
/// dereferences, e.g. changing `*x` to `x` within the function.
///
/// **Example:**
/// ```rust
/// fn foo(ref x: u8) -> bool { .. }
/// ```
declare_clippy_lint! {
pub TOPLEVEL_REF_ARG,
style,
"an entire binding declared as `ref`, in a function argument or a `let` statement"
}
/// **What it does:** Checks for comparisons to NaN.
///
/// **Why is this bad?** NaN does not compare meaningfully to anything not
/// even itself so those comparisons are simply wrong.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// x == NAN
/// ```
declare_clippy_lint! {
pub CMP_NAN,
correctness,
"comparisons to NAN, which will always return false, probably not intended"
}
/// **What it does:** Checks for (in-)equality comparisons on floating-point
/// values (apart from zero), except in functions called `*eq*` (which probably
/// implement equality for a type involving floats).
///
/// **Why is this bad?** Floating point calculations are usually imprecise, so
/// asking if two values are *exactly* equal is asking for trouble. For a good
/// guide on what to do, see [the floating point
/// guide](http://www.floating-point-gui.de/errors/comparison).
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// y == 1.23f64
/// y != x // where both are floats
/// ```
declare_clippy_lint! {
pub FLOAT_CMP,
correctness,
"using `==` or `!=` on float values instead of comparing difference with an epsilon"
}
/// **What it does:** Checks for conversions to owned values just for the sake
/// of a comparison.
///
/// **Why is this bad?** The comparison can operate on a reference, so creating
/// an owned value effectively throws it away directly afterwards, which is
/// needlessly consuming code and heap space.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// x.to_owned() == y
/// ```
declare_clippy_lint! {
pub CMP_OWNED,
perf,
"creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`"
}
/// **What it does:** Checks for getting the remainder of a division by one.
///
/// **Why is this bad?** The result can only ever be zero. No one will write
/// such code deliberately, unless trying to win an Underhanded Rust
/// Contest. Even for that contest, it's probably a bad idea. Use something more
/// underhanded.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// x % 1
/// ```
declare_clippy_lint! {
pub MODULO_ONE,
correctness,
"taking a number modulo 1, which always returns 0"
}
/// **What it does:** Checks for patterns in the form `name @ _`.
///
/// **Why is this bad?** It's almost always more readable to just use direct
/// bindings.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// match v {
/// Some(x) => (),
/// y @ _ => (), // easier written as `y`,
/// }
/// ```
declare_clippy_lint! {
pub REDUNDANT_PATTERN,
style,
"using `name @ _` in a pattern"
}
/// **What it does:** Checks for the use of bindings with a single leading
/// underscore.
///
/// **Why is this bad?** A single leading underscore is usually used to indicate
/// that a binding will not be used. Using such a binding breaks this
/// expectation.
///
/// **Known problems:** The lint does not work properly with desugaring and
/// macro, it has been allowed in the mean time.
///
/// **Example:**
/// ```rust
/// let _x = 0;
/// let y = _x + 1; // Here we are using `_x`, even though it has a leading
/// // underscore. We should rename `_x` to `x`
/// ```
declare_clippy_lint! {
pub USED_UNDERSCORE_BINDING,
pedantic,
"using a binding which is prefixed with an underscore"
}
/// **What it does:** Checks for the use of short circuit boolean conditions as
/// a
/// statement.
///
/// **Why is this bad?** Using a short circuit boolean condition as a statement
/// may hide the fact that the second part is executed or not depending on the
/// outcome of the first part.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// f() && g(); // We should write `if f() { g(); }`.
/// ```
declare_clippy_lint! {
pub SHORT_CIRCUIT_STATEMENT,
complexity,
"using a short circuit boolean condition as a statement"
}
/// **What it does:** Catch casts from `0` to some pointer type
///
/// **Why is this bad?** This generally means `null` and is better expressed as
/// {`std`, `core`}`::ptr::`{`null`, `null_mut`}.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// 0 as *const u32
/// ```
declare_clippy_lint! {
pub ZERO_PTR,
style,
"using 0 as *{const, mut} T"
}
/// **What it does:** Checks for (in-)equality comparisons on floating-point
/// value and constant, except in functions called `*eq*` (which probably
/// implement equality for a type involving floats).
///
/// **Why is this bad?** Floating point calculations are usually imprecise, so
/// asking if two values are *exactly* equal is asking for trouble. For a good
/// guide on what to do, see [the floating point
/// guide](http://www.floating-point-gui.de/errors/comparison).
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// const ONE == 1.00f64
/// x == ONE // where both are floats
/// ```
declare_clippy_lint! {
pub FLOAT_CMP_CONST,
restriction,
"using `==` or `!=` on float constants instead of comparing difference with an epsilon"
}
#[derive(Copy, Clone)]
pub struct Pass;
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array!(
TOPLEVEL_REF_ARG,
CMP_NAN,
FLOAT_CMP,
CMP_OWNED,
MODULO_ONE,
REDUNDANT_PATTERN,
USED_UNDERSCORE_BINDING,
SHORT_CIRCUIT_STATEMENT,
ZERO_PTR,
FLOAT_CMP_CONST
)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_fn(
&mut self,
cx: &LateContext<'a, 'tcx>,
k: FnKind<'tcx>,
decl: &'tcx FnDecl,
body: &'tcx Body,
_: Span,
_: NodeId,
) {
if let FnKind::Closure(_) = k {
// Does not apply to closures
return;
}
for arg in iter_input_pats(decl, body) {
match arg.pat.node {
PatKind::Binding(BindingAnnotation::Ref, _, _, _) |
PatKind::Binding(BindingAnnotation::RefMut, _, _, _) => {
span_lint(
cx,
TOPLEVEL_REF_ARG,
arg.pat.span,
"`ref` directly on a function argument is ignored. Consider using a reference type \
instead.",
);
},
_ => {},
}
}
}
fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, s: &'tcx Stmt) {
if_chain! {
if let StmtDecl(ref d, _) = s.node;
if let DeclLocal(ref l) = d.node;
if let PatKind::Binding(an, _, i, None) = l.pat.node;
if let Some(ref init) = l.init;
then {
if an == BindingAnnotation::Ref || an == BindingAnnotation::RefMut {
let init = Sugg::hir(cx, init, "..");
let (mutopt,initref) = if an == BindingAnnotation::RefMut {
("mut ", init.mut_addr())
} else {
("", init.addr())
};
let tyopt = if let Some(ref ty) = l.ty {
format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_"))
} else {
"".to_owned()
};
span_lint_and_then(cx,
TOPLEVEL_REF_ARG,
l.pat.span,
"`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
|db| {
db.span_suggestion(s.span,
"try",
format!("let {name}{tyopt} = {initref};",
name=snippet(cx, i.span, "_"),
tyopt=tyopt,
initref=initref));
}
);
}
}
};
if_chain! {
if let StmtSemi(ref expr, _) = s.node;
if let Expr_::ExprBinary(ref binop, ref a, ref b) = expr.node;
if binop.node == BiAnd || binop.node == BiOr;
if let Some(sugg) = Sugg::hir_opt(cx, a);
then {
span_lint_and_then(cx,
SHORT_CIRCUIT_STATEMENT,
s.span,
"boolean short circuit operator in statement may be clearer using an explicit test",
|db| {
let sugg = if binop.node == BiOr { !sugg } else { sugg };
db.span_suggestion(s.span, "replace it with",
format!("if {} {{ {}; }}", sugg, &snippet(cx, b.span, "..")));
});
}
};
}
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
match expr.node {
ExprCast(ref e, ref ty) => {
check_cast(cx, expr.span, e, ty);
return;
},
ExprBinary(ref cmp, ref left, ref right) => {
let op = cmp.node;
if op.is_comparison() {
if let ExprPath(QPath::Resolved(_, ref path)) = left.node {
check_nan(cx, path, expr);
}
if let ExprPath(QPath::Resolved(_, ref path)) = right.node {
check_nan(cx, path, expr);
}
check_to_owned(cx, left, right);
check_to_owned(cx, right, left);
}
if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
if is_allowed(cx, left) || is_allowed(cx, right) {
return;
}
if let Some(name) = get_item_name(cx, expr) {
let name = name.as_str();
if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_")
|| name.ends_with("_eq")
{
return;
}
}
let (lint, msg) = if is_named_constant(cx, left) || is_named_constant(cx, right) {
(FLOAT_CMP_CONST, "strict comparison of f32 or f64 constant")
} else {
(FLOAT_CMP, "strict comparison of f32 or f64")
};
span_lint_and_then(cx, lint, expr.span, msg, |db| {
let lhs = Sugg::hir(cx, left, "..");
let rhs = Sugg::hir(cx, right, "..");
db.span_suggestion(
expr.span,
"consider comparing them within some error",
format!("({}).abs() < error", lhs - rhs),
);
db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available.");
});
} else if op == BiRem && is_integer_literal(right, 1) {
span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
}
},
_ => {},
}
if in_attributes_expansion(expr) {
// Don't lint things expanded by #[derive(...)], etc
return;
}
let binding = match expr.node {
ExprPath(ref qpath) => {
let binding = last_path_segment(qpath).name.as_str();
if binding.starts_with('_') &&
!binding.starts_with("__") &&
binding != "_result" && // FIXME: #944
is_used(cx, expr) &&
// don't lint if the declaration is in a macro
non_macro_local(cx, &cx.tables.qpath_def(qpath, expr.hir_id))
{
Some(binding)
} else {
None
}
},
ExprField(_, spanned) => {
let name = spanned.node.as_str();
if name.starts_with('_') && !name.starts_with("__") {
Some(name)
} else {
None
}
},
_ => None,
};
if let Some(binding) = binding {
span_lint(
cx,
USED_UNDERSCORE_BINDING,
expr.span,
&format!(
"used binding `{}` which is prefixed with an underscore. A leading \
underscore signals that a binding will not be used.",
binding
),
);
}
}
fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
if let PatKind::Binding(_, _, ref ident, Some(ref right)) = pat.node {
if right.node == PatKind::Wild {
span_lint(
cx,
REDUNDANT_PATTERN,
pat.span,
&format!("the `{} @ _` pattern can be written as just `{}`", ident.node, ident.node),
);
}
}
}
}
fn check_nan(cx: &LateContext, path: &Path, expr: &Expr) {
if !in_constant(cx, expr.id) {
if let Some(seg) = path.segments.last() {
if seg.name == "NAN" {
span_lint(
cx,
CMP_NAN,
expr.span,
"doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead",
);
}
}
}
}
fn is_named_constant<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
if let Some((_, res)) = constant(cx, cx.tables, expr) {
res
} else {
false
}
}
fn is_allowed<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
match constant(cx, cx.tables, expr) {
Some((Constant::F32(f), _)) => f == 0.0 || f.is_infinite(),
Some((Constant::F64(f), _)) => f == 0.0 || f.is_infinite(),
_ => false,
}
}
fn is_float(cx: &LateContext, expr: &Expr) -> bool {
matches!(walk_ptrs_ty(cx.tables.expr_ty(expr)).sty, ty::TyFloat(_))
}
fn check_to_owned(cx: &LateContext, expr: &Expr, other: &Expr) {
let (arg_ty, snip) = match expr.node {
ExprMethodCall(.., ref args) if args.len() == 1 => {
if match_trait_method(cx, expr, &paths::TO_STRING) || match_trait_method(cx, expr, &paths::TO_OWNED) {
(cx.tables.expr_ty_adjusted(&args[0]), snippet(cx, args[0].span, ".."))
} else {
return;
}
},
ExprCall(ref path, ref v) if v.len() == 1 => if let ExprPath(ref path) = path.node {
if match_qpath(path, &["String", "from_str"]) || match_qpath(path, &["String", "from"]) {
(cx.tables.expr_ty_adjusted(&v[0]), snippet(cx, v[0].span, ".."))
} else {
return;
}
} else {
return;
},
_ => return,
};
let other_ty = cx.tables.expr_ty_adjusted(other);
let partial_eq_trait_id = match cx.tcx.lang_items().eq_trait() {
Some(id) => id,
None => return,
};
// *arg impls PartialEq<other>
if !arg_ty
.builtin_deref(true)
.map_or(false, |tam| implements_trait(cx, tam.ty, partial_eq_trait_id, &[other_ty]))
// arg impls PartialEq<*other>
&& !other_ty
.builtin_deref(true)
.map_or(false, |tam| implements_trait(cx, arg_ty, partial_eq_trait_id, &[tam.ty]))
// arg impls PartialEq<other>
&& !implements_trait(cx, arg_ty, partial_eq_trait_id, &[other_ty])
{
return;
}
span_lint_and_then(
cx,
CMP_OWNED,
expr.span,
"this creates an owned instance just for comparison",
|db| {
// this is as good as our recursion check can get, we can't prove that the
// current function is
// called by
// PartialEq::eq, but we can at least ensure that this code is not part of it
let parent_fn = cx.tcx.hir.get_parent(expr.id);
let parent_impl = cx.tcx.hir.get_parent(parent_fn);
if parent_impl != CRATE_NODE_ID {
if let map::NodeItem(item) = cx.tcx.hir.get(parent_impl) {
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(id) | def::Def::Upvar(id, _, _) => !in_macro(cx.tcx.hir.span(id)),
_ => false,
}
}
fn check_cast(cx: &LateContext, span: Span, e: &Expr, ty: &Ty) {
if_chain! {
if let TyPtr(MutTy { mutbl, .. }) = ty.node;
if let ExprLit(ref lit) = e.node;
if let LitKind::Int(value, ..) = lit.node;
if value == 0;
if !in_constant(cx, e.id);
then {
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);
}
}
}