Shrink `hir::def::Res`.

[rust.git] / clippy_lints / src / neg_multiply.rs

diff --git a/clippy_lints/src/neg_multiply.rs b/clippy_lints/src/neg_multiply.rs
index 4681e990df88a1880efa4484c8aceb1ffb2ca5f5..b087cfb36b1166968c1fde2c28b3e2bd42b872a4 100644 (file)
--- a/clippy_lints/src/neg_multiply.rs
+++ b/clippy_lints/src/neg_multiply.rs
@@ -1,39 +1,50 @@
+use clippy_utils::consts::{self, Constant};
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::sugg::has_enclosing_paren;
 use if_chain::if_chain;
+use rustc_ast::util::parser::PREC_PREFIX;
+use rustc_errors::Applicability;
 use rustc_hir::{BinOpKind, Expr, ExprKind, UnOp};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
 
-use crate::consts::{self, Constant};
-use crate::utils::span_lint;
-
 declare_clippy_lint! {
-    /// **What it does:** Checks for multiplication by -1 as a form of negation.
+    /// ### What it does
+    /// Checks for multiplication by -1 as a form of negation.
+    ///
+    /// ### Why is this bad?
+    /// It's more readable to just negate.
     ///
-    /// **Why is this bad?** It's more readable to just negate.
+    /// ### Known problems
+    /// This only catches integers (for now).
     ///
-    /// **Known problems:** This only catches integers (for now).
+    /// ### Example
+    /// ```rust,ignore
+    /// let a = x * -1;
+    /// ```
     ///
-    /// **Example:**
-    /// ```ignore
-    /// x * -1
+    /// Use instead:
+    /// ```rust,ignore
+    /// let a = -x;
     /// ```
+    #[clippy::version = "pre 1.29.0"]
     pub NEG_MULTIPLY,
     style,
-    "multiplying integers with `-1`"
+    "multiplying integers by `-1`"
 }
 
 declare_lint_pass!(NegMultiply => [NEG_MULTIPLY]);
 
-#[allow(clippy::match_same_arms)]
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NegMultiply {
-    fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
-        if let ExprKind::Binary(ref op, ref left, ref right) = e.kind {
+impl<'tcx> LateLintPass<'tcx> for NegMultiply {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
+        if let ExprKind::Binary(ref op, left, right) = e.kind {
             if BinOpKind::Mul == op.node {
                 match (&left.kind, &right.kind) {
                     (&ExprKind::Unary(..), &ExprKind::Unary(..)) => {},
-                    (&ExprKind::Unary(UnOp::UnNeg, ref lit), _) => check_mul(cx, e.span, lit, right),
-                    (_, &ExprKind::Unary(UnOp::UnNeg, ref lit)) => check_mul(cx, e.span, lit, left),
+                    (&ExprKind::Unary(UnOp::Neg, lit), _) => check_mul(cx, e.span, lit, right),
+                    (_, &ExprKind::Unary(UnOp::Neg, lit)) => check_mul(cx, e.span, lit, left),
                     _ => {},
                 }
             }
@@ -41,13 +52,29 @@ fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
     }
 }
 
-fn check_mul(cx: &LateContext<'_, '_>, span: Span, lit: &Expr<'_>, exp: &Expr<'_>) {
+fn check_mul(cx: &LateContext<'_>, span: Span, lit: &Expr<'_>, exp: &Expr<'_>) {
     if_chain! {
         if let ExprKind::Lit(ref l) = lit.kind;
-        if let Constant::Int(1) = consts::lit_to_constant(&l.node, cx.tables.expr_ty_opt(lit));
-        if cx.tables.expr_ty(exp).is_integral();
+        if consts::lit_to_mir_constant(&l.node, cx.typeck_results().expr_ty_opt(lit)) == Constant::Int(1);
+        if cx.typeck_results().expr_ty(exp).is_integral();
+
         then {
-            span_lint(cx, NEG_MULTIPLY, span, "Negation by multiplying with `-1`");
+            let mut applicability = Applicability::MachineApplicable;
+            let snip = snippet_with_applicability(cx, exp.span, "..", &mut applicability);
+            let suggestion = if exp.precedence().order() < PREC_PREFIX && !has_enclosing_paren(&snip) {
+                format!("-({})", snip)
+            } else {
+                format!("-{}", snip)
+            };
+            span_lint_and_sugg(
+                    cx,
+                    NEG_MULTIPLY,
+                    span,
+                    "this multiplication by -1 can be written more succinctly",
+                    "consider using",
+                    suggestion,
+                    applicability,
+                );
         }
     }
 }