Auto merge of rust-lang#9026 - hellow554:neg_multiply_precedence, r=xFrednet

put parentheses around neg_multiply suggestion if needed

*Please write a short comment explaining your change (or "none" for internal only changes)*

changelog: [`neg_multiply`]: put parentheses around suggestion if needed

Author: bors

clippy_lints/src/neg_multiply.rs

@@ -1,7 +1,9 @@
 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};
@@ -58,7 +60,12 @@ fn check_mul(cx: &LateContext<'_>, span: Span, lit: &Expr<'_>, exp: &Expr<'_>) {
 
         then {
             let mut applicability = Applicability::MachineApplicable;
-            let suggestion = format!("-{}", snippet_with_applicability(cx, exp.span, "..", &mut applicability));
+            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,

tests/ui/neg_multiply.fixed

@@ -38,6 +38,9 @@ fn main() {
 
     0xcafe | -0xff00;
 
+    -(3_usize as i32);
+    -(3_usize as i32);
+
     -1 * -1; // should be ok
 
     X * -1; // should be ok

tests/ui/neg_multiply.rs

@@ -38,6 +38,9 @@ fn main() {
 
     0xcafe | 0xff00 * -1;
 
+    3_usize as i32 * -1;
+    (3_usize as i32) * -1;
+
     -1 * -1; // should be ok
 
     X * -1; // should be ok

tests/ui/neg_multiply.stderr

@@ -36,5 +36,17 @@ error: this multiplication by -1 can be written more succinctly
 LL |     0xcafe | 0xff00 * -1;
    |              ^^^^^^^^^^^ help: consider using: `-0xff00`
 
-error: aborting due to 6 previous errors
+error: this multiplication by -1 can be written more succinctly
+  --> $DIR/neg_multiply.rs:41:5
+   |
+LL |     3_usize as i32 * -1;
+   |     ^^^^^^^^^^^^^^^^^^^ help: consider using: `-(3_usize as i32)`
+
+error: this multiplication by -1 can be written more succinctly
+  --> $DIR/neg_multiply.rs:42:5
+   |
+LL |     (3_usize as i32) * -1;
+   |     ^^^^^^^^^^^^^^^^^^^^^ help: consider using: `-(3_usize as i32)`
+
+error: aborting due to 8 previous errors