Actually check for constants.

clippy_lints/src/arithmetic.rs

@@ -1,3 +1,4 @@
+use crate::consts::constant_simple;
 use crate::utils::span_lint;
 use rustc::hir;
 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
@@ -92,7 +93,13 @@ fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
                 }
             },
             hir::ExprKind::Unary(hir::UnOp::UnNeg, arg) => {
-                if cx.tables.expr_ty(arg).is_floating_point() {
+                let ty = cx.tables.expr_ty(arg);
+                if ty.is_integral() {
+                    if constant_simple(cx, cx.tables, expr).is_none() {
+                        span_lint(cx, INTEGER_ARITHMETIC, expr.span, "integer arithmetic detected");
+                        self.expr_span = Some(expr.span);
+                    }
+                } else if ty.is_floating_point() {
                     span_lint(cx, FLOAT_ARITHMETIC, expr.span, "floating-point arithmetic detected");
                     self.expr_span = Some(expr.span);
                 }

tests/ui/arithmetic.rs

@@ -15,7 +15,11 @@ fn main() {
     1 %
     i / 2; // no error, this is part of the expression in the preceding line
     i - 2 + 2 - i;
-    -i; // no error, overflows are checked by `overflowing_literals`
+    -i;
+
+    // no error, overflows are checked by `overflowing_literals`
+    -1;
+    -(-1);
 
     i & 1; // no wrapping
     i | 1;

tests/ui/arithmetic.stderr

@@ -25,8 +25,14 @@ error: integer arithmetic detected
 LL |     i - 2 + 2 - i;
    |     ^^^^^^^^^^^^^
 
+error: integer arithmetic detected
+  --> $DIR/arithmetic.rs:18:5
+   |
+LL |     -i;
+   |     ^^
+
 error: floating-point arithmetic detected
-  --> $DIR/arithmetic.rs:28:5
+  --> $DIR/arithmetic.rs:32:5
    |
 LL |     f * 2.0;
    |     ^^^^^^^
@@ -34,34 +40,34 @@ LL |     f * 2.0;
    = note: `-D clippy::float-arithmetic` implied by `-D warnings`
 
 error: floating-point arithmetic detected
-  --> $DIR/arithmetic.rs:30:5
+  --> $DIR/arithmetic.rs:34:5
    |
 LL |     1.0 + f;
    |     ^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/arithmetic.rs:31:5
+  --> $DIR/arithmetic.rs:35:5
    |
 LL |     f * 2.0;
    |     ^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/arithmetic.rs:32:5
+  --> $DIR/arithmetic.rs:36:5
    |
 LL |     f / 2.0;
    |     ^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/arithmetic.rs:33:5
+  --> $DIR/arithmetic.rs:37:5
    |
 LL |     f - 2.0 * 4.2;
    |     ^^^^^^^^^^^^^
 
 error: floating-point arithmetic detected
-  --> $DIR/arithmetic.rs:34:5
+  --> $DIR/arithmetic.rs:38:5
    |
 LL |     -f;
    |     ^^
 
-error: aborting due to 10 previous errors
+error: aborting due to 11 previous errors