Add test case for negative literals

clippy_lints/src/types.rs

@@ -1601,7 +1601,7 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
             let (cast_from, cast_to) = (cx.typeck_results().expr_ty(ex), cx.typeck_results().expr_ty(expr));
             lint_fn_to_numeric_cast(cx, expr, ex, cast_from, cast_to);
             if let Some(lit) = get_numeric_literal(ex) {
-                let literal_str = snippet_opt(cx, lit.span).unwrap_or_default();
+                let literal_str = snippet_opt(cx, ex.span).unwrap_or_default();
 
                 if_chain! {
                     if let LitKind::Int(n, _) = lit.node;

tests/ui/unnecessary_cast_fixable.fixed

@@ -29,4 +29,7 @@ fn main() {
     0.5_f32;
 
     1.0 as u16;
+
+    -1_i32;
+    -1.0_f32;
 }

tests/ui/unnecessary_cast_fixable.rs

@@ -29,4 +29,7 @@ fn main() {
     0.5 as f32;
 
     1.0 as u16;
+
+    -1 as i32;
+    -1.0 as f32;
 }

tests/ui/unnecessary_cast_fixable.stderr

@@ -60,5 +60,17 @@ error: casting float literal to `f32` is unnecessary
 LL |     0.5 as f32;
    |     ^^^^^^^^^^ help: try: `0.5_f32`
 
-error: aborting due to 10 previous errors
+error: casting integer literal to `i32` is unnecessary
+  --> $DIR/unnecessary_cast_fixable.rs:33:5
+   |
+LL |     -1 as i32;
+   |     ^^^^^^^^^ help: try: `-1_i32`
+
+error: casting float literal to `f32` is unnecessary
+  --> $DIR/unnecessary_cast_fixable.rs:34:5
+   |
+LL |     -1.0 as f32;
+   |     ^^^^^^^^^^^ help: try: `-1.0_f32`
+
+error: aborting due to 12 previous errors