81 lines
2.7 KiB
Rust
81 lines
2.7 KiB
Rust
use clippy_utils::consts::{self, Constant};
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use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::source::snippet_with_context;
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use clippy_utils::sugg::has_enclosing_paren;
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use if_chain::if_chain;
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use rustc_ast::util::parser::PREC_PREFIX;
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use rustc_errors::Applicability;
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use rustc_hir::{BinOpKind, Expr, ExprKind, UnOp};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::Span;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for multiplication by -1 as a form of negation.
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///
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/// ### Why is this bad?
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/// It's more readable to just negate.
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///
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/// ### Known problems
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/// This only catches integers (for now).
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///
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/// ### Example
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/// ```rust,ignore
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/// let a = x * -1;
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/// ```
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///
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/// Use instead:
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/// ```rust,ignore
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/// let a = -x;
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub NEG_MULTIPLY,
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style,
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"multiplying integers by `-1`"
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}
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declare_lint_pass!(NegMultiply => [NEG_MULTIPLY]);
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impl<'tcx> LateLintPass<'tcx> for NegMultiply {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
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if let ExprKind::Binary(ref op, left, right) = e.kind {
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if BinOpKind::Mul == op.node {
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match (&left.kind, &right.kind) {
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(&ExprKind::Unary(..), &ExprKind::Unary(..)) => {},
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(&ExprKind::Unary(UnOp::Neg, lit), _) => check_mul(cx, e.span, lit, right),
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(_, &ExprKind::Unary(UnOp::Neg, lit)) => check_mul(cx, e.span, lit, left),
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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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fn check_mul(cx: &LateContext<'_>, span: Span, lit: &Expr<'_>, exp: &Expr<'_>) {
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if_chain! {
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if let ExprKind::Lit(l) = lit.kind;
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if consts::lit_to_mir_constant(&l.node, cx.typeck_results().expr_ty_opt(lit)) == Constant::Int(1);
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if cx.typeck_results().expr_ty(exp).is_integral();
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then {
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let mut applicability = Applicability::MachineApplicable;
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let (snip, from_macro) = snippet_with_context(cx, exp.span, span.ctxt(), "..", &mut applicability);
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let suggestion = if !from_macro && exp.precedence().order() < PREC_PREFIX && !has_enclosing_paren(&snip) {
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format!("-({snip})")
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} else {
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format!("-{snip}")
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};
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span_lint_and_sugg(
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cx,
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NEG_MULTIPLY,
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span,
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"this multiplication by -1 can be written more succinctly",
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"consider using",
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suggestion,
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applicability,
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);
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}
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}
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}
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