459 lines
16 KiB
Rust
459 lines
16 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 syntax::codemap::{Span, Spanned, ExpnFormat};
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use syntax::ptr::P;
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use utils::{
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get_item_name, get_parent_expr, implements_trait, is_integer_literal, match_path, snippet,
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span_lint, span_lint_and_then, walk_ptrs_ty
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};
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/// **What it does:** This lint 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 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! {
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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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}
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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 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, 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 PatKind::Binding(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!(": {}", 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 {}{} = &{};",
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snippet(cx, i.span, "_"),
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tyopt,
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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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}
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/// **What it does:** This lint 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 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 cmp.node.is_comparison() {
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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| {
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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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/// **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).
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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) {
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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(cx,
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FLOAT_CMP,
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expr.span,
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&format!("{}-comparison of f32 or f64 detected. Consider changing this to `({} - {}).abs() < \
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epsilon` for some suitable value of epsilon. \
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std::f32::EPSILON and std::f64::EPSILON are available.",
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op.as_str(),
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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(ConstVal::Float(val)) = res {
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val == 0.0 || val == ::std::f64::INFINITY || val == ::std::f64::NEG_INFINITY
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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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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.
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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 cmp.node.is_comparison() {
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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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}
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}
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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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if name.as_str() == "to_string" || name.as_str() == "to_owned" && is_str_arg(cx, args) {
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(cx.tcx.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(None, 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.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.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: &[P<Expr>]) -> bool {
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args.len() == 1 &&
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if let ty::TyStr = walk_ptrs_ty(cx.tcx.expr_ty(&args[0])).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 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 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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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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}
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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 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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/// **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:** The lint does not work properly with desugaring and macro, it has been
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/// allowed in the mean time.
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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, Allow,
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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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#[cfg_attr(rustfmt, rustfmt_skip)]
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fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
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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 path) => {
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let segment = path.segments
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.last()
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.expect("path should always have at least one segment")
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.name;
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if segment.as_str().starts_with('_') &&
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!segment.as_str().starts_with("__") &&
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segment != segment.unhygienize() && // not in bang macro
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is_used(cx, expr) {
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Some(segment.as_str())
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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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if binding != "_result" { // FIXME: #944
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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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}
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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(ref 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| {
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match info.callee.format {
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ExpnFormat::MacroAttribute(_) => true,
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_ => false,
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}
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})
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})
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}
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