mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-19 09:33:36 +00:00
385 lines
14 KiB
Rust
385 lines
14 KiB
Rust
use rustc::lint::*;
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use syntax::ptr::P;
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use rustc_front::hir::*;
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use reexport::*;
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use rustc_front::util::{is_comparison_binop, binop_to_string};
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use syntax::codemap::{Span, Spanned};
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use rustc_front::intravisit::FnKind;
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use rustc::middle::ty;
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use rustc::middle::const_eval::ConstVal::Float;
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use rustc::middle::const_eval::eval_const_expr_partial;
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use rustc::middle::const_eval::EvalHint::ExprTypeChecked;
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use utils::{get_item_name, match_path, snippet, get_parent_expr, span_lint, walk_ptrs_ty,
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is_integer_literal};
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use utils::span_help_and_lint;
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/// **What it does:** This lint checks for function arguments and let bindings denoted as `ref`. It is `Warn` by default.
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///
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/// **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.
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///
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/// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The 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, removing the `ref` will lead to errors. This can be fixed by removing the dereferences, e.g. changing `*x` to `x` within the function.
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///
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/// **Example:** `fn foo(ref x: u8) -> bool { .. }`
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declare_lint!(pub TOPLEVEL_REF_ARG, Warn,
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"An entire binding was declared as `ref`, in a function argument (`fn foo(ref x: Bar)`), \
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or a `let` statement (`let ref x = foo()`). In such cases, it is preferred to take \
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references with `&`.");
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#[allow(missing_copy_implementations)]
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pub struct TopLevelRefPass;
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impl LintPass for TopLevelRefPass {
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fn get_lints(&self) -> LintArray {
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lint_array!(TOPLEVEL_REF_ARG)
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}
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}
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impl LateLintPass for TopLevelRefPass {
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fn check_fn(&mut self, cx: &LateContext, k: FnKind, decl: &FnDecl, _: &Block, _: Span, _: 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 ref arg in &decl.inputs {
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if let PatIdent(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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}
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fn check_stmt(&mut self, cx: &LateContext, s: &Stmt) {
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if_let_chain! {
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[
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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 PatIdent(BindByRef(_), i, None) = l.pat.node,
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let Some(ref init) = l.init
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], {
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let tyopt = if let Some(ref ty) = l.ty {
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format!(": {:?} ", ty)
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} else {
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"".to_owned()
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};
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span_help_and_lint(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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&format!("try `let {} {}= &{};`", snippet(cx, i.span, "_"),
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tyopt, snippet(cx, init.span, "_"))
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);
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}
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};
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}
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}
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/// **What it does:** This lint checks for comparisons to NAN. It is `Deny` by default.
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///
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/// **Why is this bad?** NAN does not compare meaningfully to anything – not 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:** `x == NAN`
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declare_lint!(pub CMP_NAN, Deny,
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"comparisons to NAN (which will always return false, which is probably not intended)");
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#[derive(Copy,Clone)]
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pub struct CmpNan;
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impl LintPass for CmpNan {
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fn get_lints(&self) -> LintArray {
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lint_array!(CMP_NAN)
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}
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}
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impl LateLintPass for CmpNan {
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fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
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if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
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if is_comparison_binop(cmp.node) {
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if let ExprPath(_, 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(_, ref path) = right.node {
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check_nan(cx, path, expr.span);
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}
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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| if seg.identifier.name.as_str() == "NAN" {
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span_lint(cx, CMP_NAN, 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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/// **What it does:** This lint 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). It is `Warn` by default.
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///
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/// **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).
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///
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/// **Known problems:** None
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///
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/// **Example:** `y == 1.23f64`
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declare_lint!(pub FLOAT_CMP, Warn,
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"using `==` or `!=` on float values (as floating-point operations \
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usually involve rounding errors, it is always better to check for approximate \
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equality within small bounds)");
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#[derive(Copy,Clone)]
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pub struct FloatCmp;
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impl LintPass for FloatCmp {
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fn get_lints(&self) -> LintArray {
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lint_array!(FLOAT_CMP)
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}
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}
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impl LateLintPass for FloatCmp {
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fn check_expr(&mut self, cx: &LateContext, expr: &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 == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
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if is_allowed(cx, left) || is_allowed(cx, right) { return; }
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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" ||
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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(cx, FLOAT_CMP, expr.span, &format!(
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"{}-comparison of f32 or f64 detected. Consider changing this to \
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`abs({} - {}) < epsilon` for some suitable value of epsilon",
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binop_to_string(op), snippet(cx, left.span, ".."),
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snippet(cx, right.span, "..")));
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}
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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(Float(val)) = res {
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val == 0.0 || val == ::std::f64::INFINITY || val == ::std::f64::NEG_INFINITY
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} else { false }
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}
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fn is_float(cx: &LateContext, expr: &Expr) -> bool {
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if let ty::TyFloat(_) = walk_ptrs_ty(cx.tcx.expr_ty(expr)).sty {
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true
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} else {
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false
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}
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}
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/// **What it does:** This lint checks for conversions to owned values just for the sake of a comparison. It is `Warn` by default.
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///
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/// **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.
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///
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/// **Known problems:** None
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///
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/// **Example:** `x.to_owned() == y`
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declare_lint!(pub CMP_OWNED, Warn,
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"creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`");
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#[derive(Copy,Clone)]
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pub struct CmpOwned;
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impl LintPass for CmpOwned {
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fn get_lints(&self) -> LintArray {
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lint_array!(CMP_OWNED)
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}
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}
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impl LateLintPass for CmpOwned {
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fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
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if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
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if is_comparison_binop(cmp.node) {
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check_to_owned(cx, left, right.span, true, cmp.span);
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check_to_owned(cx, right, left.span, false, cmp.span)
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}
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}
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}
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}
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fn check_to_owned(cx: &LateContext, expr: &Expr, other_span: Span, left: bool, op: Span) {
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let snip = match expr.node {
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ExprMethodCall(Spanned{node: ref name, ..}, _, ref args) if args.len() == 1 => {
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if name.as_str() == "to_string" ||
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name.as_str() == "to_owned" && is_str_arg(cx, args) {
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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(None, ref path) = path.node {
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if match_path(path, &["String", "from_str"]) ||
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match_path(path, &["String", "from"]) {
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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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if left {
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span_lint(cx, CMP_OWNED, expr.span, &format!(
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"this creates an owned instance just for comparison. Consider using \
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`{} {} {}` to compare without allocation", snip,
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snippet(cx, op, "=="), snippet(cx, other_span, "..")));
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} else {
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span_lint(cx, CMP_OWNED, expr.span, &format!(
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"this creates an owned instance just for comparison. Consider using \
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`{} {} {}` to compare without allocation",
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snippet(cx, other_span, ".."), snippet(cx, op, "=="), snip));
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}
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}
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fn is_str_arg(cx: &LateContext, args: &[P<Expr>]) -> bool {
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args.len() == 1 && if let ty::TyStr =
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walk_ptrs_ty(cx.tcx.expr_ty(&args[0])).sty { true } else { false }
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}
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/// **What it does:** This lint checks for getting the remainder of a division by one. It is `Warn` by default.
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///
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/// **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.
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///
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/// **Known problems:** None
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///
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/// **Example:** `x % 1`
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declare_lint!(pub MODULO_ONE, Warn, "taking a number modulo 1, which always returns 0");
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#[derive(Copy,Clone)]
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pub struct ModuloOne;
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impl LintPass for ModuloOne {
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fn get_lints(&self) -> LintArray {
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lint_array!(MODULO_ONE)
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}
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}
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impl LateLintPass for ModuloOne {
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fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
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if let ExprBinary(ref cmp, _, ref right) = expr.node {
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if let Spanned {node: BinOp_::BiRem, ..} = *cmp {
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if is_integer_literal(right, 1) {
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cx.span_lint(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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}
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/// **What it does:** This lint 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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/// ```
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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!(pub REDUNDANT_PATTERN, Warn, "using `name @ _` in a pattern");
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#[derive(Copy,Clone)]
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pub struct PatternPass;
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impl LintPass for PatternPass {
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fn get_lints(&self) -> LintArray {
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lint_array!(REDUNDANT_PATTERN)
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}
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}
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impl LateLintPass for PatternPass {
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fn check_pat(&mut self, cx: &LateContext, pat: &Pat) {
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if let PatIdent(_, ref ident, Some(ref right)) = pat.node {
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if right.node == PatWild {
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cx.span_lint(REDUNDANT_PATTERN, pat.span, &format!(
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"the `{} @ _` pattern can be written as just `{}`",
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ident.node.name, ident.node.name));
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}
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}
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}
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}
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/// **What it does:** This lint 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 that a binding
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/// will not be used. Using such a binding breaks this expectation.
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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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/// 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!(pub USED_UNDERSCORE_BINDING, Warn,
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"using a binding which is prefixed with an underscore");
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#[derive(Copy, Clone)]
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pub struct UsedUnderscoreBinding;
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impl LintPass for UsedUnderscoreBinding {
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fn get_lints(&self) -> LintArray {
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lint_array!(USED_UNDERSCORE_BINDING)
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}
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}
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impl LateLintPass for UsedUnderscoreBinding {
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fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
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let needs_lint = match expr.node {
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ExprPath(_, ref path) => {
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let ident = path.segments.last()
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.expect("path should always have at least one segment")
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.identifier;
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ident.name.as_str().chars().next() == Some('_') //starts with '_'
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&& ident.name.as_str().chars().skip(1).next() != Some('_') //doesn't start with "__"
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&& ident.name != ident.unhygienic_name //not in macro
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&& is_used(cx, expr)
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},
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ExprField(_, spanned) => {
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let name = spanned.node.as_str();
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name.chars().next() == Some('_')
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&& name.chars().skip(1).next() != Some('_')
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},
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_ => false
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};
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if needs_lint {
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cx.span_lint(USED_UNDERSCORE_BINDING, expr.span,
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"used binding which is prefixed with an underscore. A leading underscore \
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signals that a binding will not be used.");
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}
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}
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}
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fn is_used(cx: &LateContext, expr: &Expr) -> bool {
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if let Some(ref parent) = get_parent_expr(cx, expr) {
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match parent.node {
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ExprAssign(_, ref rhs) => **rhs == *expr,
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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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}
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else {
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true
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}
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}
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