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 d5e1ea6d242deb787074e85963d050e3c947860f..b087cfb36b1166968c1fde2c28b3e2bd42b872a4 100644 (file)
--- a/clippy_lints/src/neg_multiply.rs
+++ b/clippy_lints/src/neg_multiply.rs
@@ -1,30 +1,42 @@
 use clippy_utils::consts::{self, Constant};
-use clippy_utils::diagnostics::span_lint;
+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;
 
 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:**
-    /// ```ignore
-    /// x * -1
+    /// ### Example
+    /// ```rust,ignore
+    /// let a = 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<'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 {
@@ -43,10 +55,26 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx 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.typeck_results().expr_ty_opt(lit));
+        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,
+                );
         }
     }
 }