361 lines
13 KiB
Rust
361 lines
13 KiB
Rust
use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg, span_lint_hir_and_then};
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use clippy_utils::source::{snippet, snippet_opt, snippet_with_context};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir::intravisit::FnKind;
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use rustc_hir::{
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self as hir, def, BinOpKind, BindingAnnotation, Body, ByRef, Expr, ExprKind, FnDecl, Mutability, PatKind, Stmt,
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StmtKind, TyKind,
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};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::lint::in_external_macro;
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use rustc_session::{declare_tool_lint, impl_lint_pass};
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use rustc_span::def_id::LocalDefId;
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use rustc_span::hygiene::DesugaringKind;
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use rustc_span::source_map::{ExpnKind, Span};
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use clippy_utils::sugg::Sugg;
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use clippy_utils::{
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get_parent_expr, in_constant, is_integer_literal, is_lint_allowed, is_no_std_crate, iter_input_pats,
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last_path_segment, SpanlessEq,
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};
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use crate::ref_patterns::REF_PATTERNS;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for function arguments and let bindings denoted as
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/// `ref`.
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///
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/// ### Why is this bad?
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/// 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
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/// 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) {}
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/// ```
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///
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/// Use instead:
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/// ```rust
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/// fn foo(_x: &u8) {}
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub TOPLEVEL_REF_ARG,
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style,
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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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declare_clippy_lint! {
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/// ### What it does
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/// Checks for the use of bindings with a single leading
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/// underscore.
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///
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/// ### Why is this bad?
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/// 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
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/// 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
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/// // underscore. We should rename `_x` to `x`
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub USED_UNDERSCORE_BINDING,
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pedantic,
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"using a binding which is prefixed with an underscore"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for the use of short circuit boolean conditions as
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/// a
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/// statement.
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///
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/// ### Why is this bad?
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/// Using a short circuit boolean condition as a statement
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/// may hide the fact that the second part is executed or not depending on the
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/// outcome of the first part.
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///
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/// ### Example
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/// ```rust,ignore
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/// f() && g(); // We should write `if f() { g(); }`.
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub SHORT_CIRCUIT_STATEMENT,
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complexity,
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"using a short circuit boolean condition as a statement"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Catch casts from `0` to some pointer type
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///
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/// ### Why is this bad?
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/// This generally means `null` and is better expressed as
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/// {`std`, `core`}`::ptr::`{`null`, `null_mut`}.
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///
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/// ### Example
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/// ```rust
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/// let a = 0 as *const u32;
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/// ```
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///
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/// Use instead:
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/// ```rust
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/// let a = std::ptr::null::<u32>();
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub ZERO_PTR,
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style,
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"using `0 as *{const, mut} T`"
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}
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pub struct LintPass {
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std_or_core: &'static str,
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}
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impl Default for LintPass {
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fn default() -> Self {
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Self { std_or_core: "std" }
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}
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}
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impl_lint_pass!(LintPass => [
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TOPLEVEL_REF_ARG,
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USED_UNDERSCORE_BINDING,
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SHORT_CIRCUIT_STATEMENT,
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ZERO_PTR,
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]);
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impl<'tcx> LateLintPass<'tcx> for LintPass {
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fn check_crate(&mut self, cx: &LateContext<'_>) {
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if is_no_std_crate(cx) {
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self.std_or_core = "core";
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}
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}
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fn check_fn(
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&mut self,
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cx: &LateContext<'tcx>,
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k: FnKind<'tcx>,
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decl: &'tcx FnDecl<'_>,
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body: &'tcx Body<'_>,
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span: Span,
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_: LocalDefId,
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) {
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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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if in_external_macro(cx.tcx.sess, span) {
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return;
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}
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for arg in iter_input_pats(decl, body) {
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// Do not emit if clippy::ref_patterns is not allowed to avoid having two lints for the same issue.
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if !is_lint_allowed(cx, REF_PATTERNS, arg.pat.hir_id) {
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return;
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}
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if let PatKind::Binding(BindingAnnotation(ByRef::Yes, _), ..) = arg.pat.kind {
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span_lint(
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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. \
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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<'tcx>, stmt: &'tcx Stmt<'_>) {
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if_chain! {
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if !in_external_macro(cx.tcx.sess, stmt.span);
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if let StmtKind::Local(local) = stmt.kind;
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if let PatKind::Binding(BindingAnnotation(ByRef::Yes, mutabl), .., name, None) = local.pat.kind;
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if let Some(init) = local.init;
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// Do not emit if clippy::ref_patterns is not allowed to avoid having two lints for the same issue.
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if is_lint_allowed(cx, REF_PATTERNS, local.pat.hir_id);
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then {
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let ctxt = local.span.ctxt();
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let mut app = Applicability::MachineApplicable;
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let sugg_init = Sugg::hir_with_context(cx, init, ctxt, "..", &mut app);
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let (mutopt, initref) = if mutabl == Mutability::Mut {
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("mut ", sugg_init.mut_addr())
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} else {
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("", sugg_init.addr())
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};
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let tyopt = if let Some(ty) = local.ty {
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let ty_snip = snippet_with_context(cx, ty.span, ctxt, "_", &mut app).0;
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format!(": &{mutopt}{ty_snip}")
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} else {
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String::new()
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};
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span_lint_hir_and_then(
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cx,
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TOPLEVEL_REF_ARG,
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init.hir_id,
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local.pat.span,
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"`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
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|diag| {
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diag.span_suggestion(
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stmt.span,
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"try",
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format!(
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"let {name}{tyopt} = {initref};",
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name=snippet(cx, name.span, ".."),
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),
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app,
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);
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}
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);
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}
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};
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if_chain! {
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if let StmtKind::Semi(expr) = stmt.kind;
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if let ExprKind::Binary(ref binop, a, b) = expr.kind;
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if binop.node == BinOpKind::And || binop.node == BinOpKind::Or;
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if let Some(sugg) = Sugg::hir_opt(cx, a);
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then {
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span_lint_hir_and_then(
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cx,
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SHORT_CIRCUIT_STATEMENT,
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expr.hir_id,
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stmt.span,
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"boolean short circuit operator in statement may be clearer using an explicit test",
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|diag| {
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let sugg = if binop.node == BinOpKind::Or { !sugg } else { sugg };
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diag.span_suggestion(
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stmt.span,
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"replace it with",
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format!(
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"if {sugg} {{ {}; }}",
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&snippet(cx, b.span, ".."),
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),
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Applicability::MachineApplicable, // snippet
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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_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if let ExprKind::Cast(e, ty) = expr.kind {
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self.check_cast(cx, expr.span, e, ty);
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return;
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}
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if in_attributes_expansion(expr) || expr.span.is_desugaring(DesugaringKind::Await) {
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// Don't lint things expanded by #[derive(...)], etc or `await` desugaring
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return;
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}
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let sym;
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let binding = match expr.kind {
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ExprKind::Path(ref qpath) if !matches!(qpath, hir::QPath::LangItem(..)) => {
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let binding = last_path_segment(qpath).ident.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.qpath_res(qpath, expr.hir_id))
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{
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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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ExprKind::Field(_, ident) => {
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sym = ident.name;
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let name = sym.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(
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cx,
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USED_UNDERSCORE_BINDING,
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expr.span,
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&format!(
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"used binding `{binding}` which is prefixed with an underscore. A leading \
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underscore signals that a binding will not be used"
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),
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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
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/// `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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get_parent_expr(cx, expr).map_or(true, |parent| match parent.kind {
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ExprKind::Assign(_, rhs, _) | ExprKind::AssignOp(_, _, rhs) => SpanlessEq::new(cx).eq_expr(rhs, expr),
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_ => is_used(cx, parent),
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})
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}
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/// Tests whether an expression is in a macro expansion (e.g., something
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/// generated by `#[derive(...)]` or the like).
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fn in_attributes_expansion(expr: &Expr<'_>) -> bool {
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use rustc_span::hygiene::MacroKind;
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if expr.span.from_expansion() {
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let data = expr.span.ctxt().outer_expn_data();
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matches!(data.kind, ExpnKind::Macro(MacroKind::Attr | MacroKind::Derive, _))
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} else {
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false
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}
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}
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/// Tests whether `res` is a variable defined outside a macro.
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fn non_macro_local(cx: &LateContext<'_>, res: def::Res) -> bool {
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if let def::Res::Local(id) = res {
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!cx.tcx.hir().span(id).from_expansion()
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} else {
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false
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}
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}
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impl LintPass {
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fn check_cast(&self, cx: &LateContext<'_>, span: Span, e: &Expr<'_>, ty: &hir::Ty<'_>) {
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if_chain! {
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if let TyKind::Ptr(ref mut_ty) = ty.kind;
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if is_integer_literal(e, 0);
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if !in_constant(cx, e.hir_id);
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then {
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let (msg, sugg_fn) = match mut_ty.mutbl {
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Mutability::Mut => ("`0 as *mut _` detected", "ptr::null_mut"),
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Mutability::Not => ("`0 as *const _` detected", "ptr::null"),
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};
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let (sugg, appl) = if let TyKind::Infer = mut_ty.ty.kind {
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(format!("{}::{sugg_fn}()", self.std_or_core), Applicability::MachineApplicable)
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} else if let Some(mut_ty_snip) = snippet_opt(cx, mut_ty.ty.span) {
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(format!("{}::{sugg_fn}::<{mut_ty_snip}>()", self.std_or_core), Applicability::MachineApplicable)
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} else {
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// `MaybeIncorrect` as type inference may not work with the suggested code
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(format!("{}::{sugg_fn}()", self.std_or_core), Applicability::MaybeIncorrect)
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};
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span_lint_and_sugg(cx, ZERO_PTR, span, msg, "try", sugg, appl);
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}
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}
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}
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}
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