diff options
Diffstat (limited to 'src/tools/clippy/clippy_lints/src/misc.rs')
| -rw-r--r-- | src/tools/clippy/clippy_lints/src/misc.rs | 342 |
1 files changed, 342 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/misc.rs b/src/tools/clippy/clippy_lints/src/misc.rs new file mode 100644 index 000000000..8224e80c9 --- /dev/null +++ b/src/tools/clippy/clippy_lints/src/misc.rs @@ -0,0 +1,342 @@ +use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg, span_lint_hir_and_then}; +use clippy_utils::source::{snippet, snippet_opt}; +use if_chain::if_chain; +use rustc_ast::ast::LitKind; +use rustc_errors::Applicability; +use rustc_hir::intravisit::FnKind; +use rustc_hir::{ + self as hir, def, BinOpKind, BindingAnnotation, Body, Expr, ExprKind, FnDecl, HirId, Mutability, PatKind, Stmt, + StmtKind, TyKind, +}; +use rustc_lint::{LateContext, LateLintPass}; +use rustc_middle::lint::in_external_macro; +use rustc_session::{declare_lint_pass, declare_tool_lint}; +use rustc_span::hygiene::DesugaringKind; +use rustc_span::source_map::{ExpnKind, Span}; + +use clippy_utils::sugg::Sugg; +use clippy_utils::{get_parent_expr, in_constant, iter_input_pats, last_path_segment, SpanlessEq}; + +declare_clippy_lint! { + /// ### 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) {} + /// ``` + /// + /// Use instead: + /// ```rust + /// fn foo(_x: &u8) {} + /// ``` + #[clippy::version = "pre 1.29.0"] + pub TOPLEVEL_REF_ARG, + style, + "an entire binding declared as `ref`, in a function argument or a `let` statement" +} +declare_clippy_lint! { + /// ### 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` + /// ``` + #[clippy::version = "pre 1.29.0"] + pub USED_UNDERSCORE_BINDING, + pedantic, + "using a binding which is prefixed with an underscore" +} + +declare_clippy_lint! { + /// ### 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. + /// + /// ### Example + /// ```rust,ignore + /// f() && g(); // We should write `if f() { g(); }`. + /// ``` + #[clippy::version = "pre 1.29.0"] + pub SHORT_CIRCUIT_STATEMENT, + complexity, + "using a short circuit boolean condition as a statement" +} + +declare_clippy_lint! { + /// ### 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`}. + /// + /// ### Example + /// ```rust + /// let a = 0 as *const u32; + /// ``` + /// + /// Use instead: + /// ```rust + /// let a = std::ptr::null::<u32>(); + /// ``` + #[clippy::version = "pre 1.29.0"] + pub ZERO_PTR, + style, + "using `0 as *{const, mut} T`" +} + +declare_lint_pass!(MiscLints => [ + TOPLEVEL_REF_ARG, + USED_UNDERSCORE_BINDING, + SHORT_CIRCUIT_STATEMENT, + ZERO_PTR, +]); + +impl<'tcx> LateLintPass<'tcx> for MiscLints { + fn check_fn( + &mut self, + cx: &LateContext<'tcx>, + k: FnKind<'tcx>, + decl: &'tcx FnDecl<'_>, + body: &'tcx Body<'_>, + span: Span, + _: HirId, + ) { + if let FnKind::Closure = k { + // Does not apply to closures + return; + } + if in_external_macro(cx.tcx.sess, span) { + return; + } + for arg in iter_input_pats(decl, body) { + if let PatKind::Binding(BindingAnnotation::Ref | BindingAnnotation::RefMut, ..) = arg.pat.kind { + 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<'tcx>, stmt: &'tcx Stmt<'_>) { + if_chain! { + if !in_external_macro(cx.tcx.sess, stmt.span); + if let StmtKind::Local(local) = stmt.kind; + if let PatKind::Binding(an, .., name, None) = local.pat.kind; + if let Some(init) = local.init; + if an == BindingAnnotation::Ref || an == BindingAnnotation::RefMut; + then { + // use the macro callsite when the init span (but not the whole local span) + // comes from an expansion like `vec![1, 2, 3]` in `let ref _ = vec![1, 2, 3];` + let sugg_init = if init.span.from_expansion() && !local.span.from_expansion() { + Sugg::hir_with_macro_callsite(cx, init, "..") + } else { + Sugg::hir(cx, init, "..") + }; + let (mutopt, initref) = if an == BindingAnnotation::RefMut { + ("mut ", sugg_init.mut_addr()) + } else { + ("", sugg_init.addr()) + }; + let tyopt = if let Some(ty) = local.ty { + format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "..")) + } else { + String::new() + }; + span_lint_hir_and_then( + cx, + TOPLEVEL_REF_ARG, + init.hir_id, + local.pat.span, + "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead", + |diag| { + diag.span_suggestion( + stmt.span, + "try", + format!( + "let {name}{tyopt} = {initref};", + name=snippet(cx, name.span, ".."), + tyopt=tyopt, + initref=initref, + ), + Applicability::MachineApplicable, + ); + } + ); + } + }; + if_chain! { + if let StmtKind::Semi(expr) = stmt.kind; + if let ExprKind::Binary(ref binop, a, b) = expr.kind; + if binop.node == BinOpKind::And || binop.node == BinOpKind::Or; + if let Some(sugg) = Sugg::hir_opt(cx, a); + then { + span_lint_hir_and_then( + cx, + SHORT_CIRCUIT_STATEMENT, + expr.hir_id, + stmt.span, + "boolean short circuit operator in statement may be clearer using an explicit test", + |diag| { + let sugg = if binop.node == BinOpKind::Or { !sugg } else { sugg }; + diag.span_suggestion( + stmt.span, + "replace it with", + format!( + "if {} {{ {}; }}", + sugg, + &snippet(cx, b.span, ".."), + ), + Applicability::MachineApplicable, // snippet + ); + }); + } + }; + } + + fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { + if let ExprKind::Cast(e, ty) = expr.kind { + check_cast(cx, expr.span, e, ty); + return; + } + if in_attributes_expansion(expr) || expr.span.is_desugaring(DesugaringKind::Await) { + // Don't lint things expanded by #[derive(...)], etc or `await` desugaring + return; + } + let sym; + let binding = match expr.kind { + ExprKind::Path(ref qpath) if !matches!(qpath, hir::QPath::LangItem(..)) => { + let binding = last_path_segment(qpath).ident.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.qpath_res(qpath, expr.hir_id)) + { + Some(binding) + } else { + None + } + }, + ExprKind::Field(_, ident) => { + sym = ident.name; + let name = sym.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 + ), + ); + } + } +} + +/// 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 { + get_parent_expr(cx, expr).map_or(true, |parent| match parent.kind { + ExprKind::Assign(_, rhs, _) | ExprKind::AssignOp(_, _, rhs) => SpanlessEq::new(cx).eq_expr(rhs, expr), + _ => is_used(cx, parent), + }) +} + +/// Tests whether an expression is in a macro expansion (e.g., something +/// generated by `#[derive(...)]` or the like). +fn in_attributes_expansion(expr: &Expr<'_>) -> bool { + use rustc_span::hygiene::MacroKind; + if expr.span.from_expansion() { + let data = expr.span.ctxt().outer_expn_data(); + matches!(data.kind, ExpnKind::Macro(MacroKind::Attr | MacroKind::Derive, _)) + } else { + false + } +} + +/// Tests whether `res` is a variable defined outside a macro. +fn non_macro_local(cx: &LateContext<'_>, res: def::Res) -> bool { + if let def::Res::Local(id) = res { + !cx.tcx.hir().span(id).from_expansion() + } else { + false + } +} + +fn check_cast(cx: &LateContext<'_>, span: Span, e: &Expr<'_>, ty: &hir::Ty<'_>) { + if_chain! { + if let TyKind::Ptr(ref mut_ty) = ty.kind; + if let ExprKind::Lit(ref lit) = e.kind; + if let LitKind::Int(0, _) = lit.node; + if !in_constant(cx, e.hir_id); + then { + let (msg, sugg_fn) = match mut_ty.mutbl { + Mutability::Mut => ("`0 as *mut _` detected", "std::ptr::null_mut"), + Mutability::Not => ("`0 as *const _` detected", "std::ptr::null"), + }; + + let (sugg, appl) = if let TyKind::Infer = mut_ty.ty.kind { + (format!("{}()", sugg_fn), Applicability::MachineApplicable) + } else if let Some(mut_ty_snip) = snippet_opt(cx, mut_ty.ty.span) { + (format!("{}::<{}>()", sugg_fn, mut_ty_snip), Applicability::MachineApplicable) + } else { + // `MaybeIncorrect` as type inference may not work with the suggested code + (format!("{}()", sugg_fn), Applicability::MaybeIncorrect) + }; + span_lint_and_sugg(cx, ZERO_PTR, span, msg, "try", sugg, appl); + } + } +} |