Lint unnecessary int-to-int and float-to-float casts

clippy_lints/src/types.rs

@@ -3,6 +3,7 @@
 use std::borrow::Cow;
 use std::cmp::Ordering;
 use std::collections::BTreeMap;
+use std::fmt::Display;
 
 use if_chain::if_chain;
 use rustc_ast::{FloatTy, IntTy, LitFloatType, LitIntType, LitKind, UintTy};
@@ -1608,18 +1609,23 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
                     let to_nbits = fp_ty_mantissa_nbits(cast_to);
                     if from_nbits != 0 && to_nbits != 0 && from_nbits <= to_nbits && num_lit.is_decimal();
                     then {
-                        span_lint_and_sugg(
-                            cx,
-                            UNNECESSARY_CAST,
-                            expr.span,
-                            &format!("casting integer literal to `{}` is unnecessary", cast_to),
-                            "try",
-                            format!("{}_{}", n, cast_to),
-                            Applicability::MachineApplicable,
-                        );
+                        show_unnecessary_cast(cx, expr, n , cast_from, cast_to);
                         return;
                     }
                 }
+
+                match lit.node {
+                    LitKind::Int(num, LitIntType::Unsuffixed) if cast_to.is_integral() => {
+                        show_unnecessary_cast(cx, expr, num, cast_from, cast_to);
+                        return;
+                    },
+                    LitKind::Float(num, LitFloatType::Unsuffixed) if cast_to.is_floating_point() => {
+                        show_unnecessary_cast(cx, expr, num, cast_from, cast_to);
+                        return;
+                    },
+                    _ => (),
+                };
+
                 match lit.node {
                     LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed) => {},
                     _ => {
@@ -1646,6 +1652,25 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
     }
 }
 
+fn show_unnecessary_cast<Num: Display>(
+    cx: &LateContext<'_>,
+    expr: &Expr<'_>,
+    num: Num,
+    cast_from: Ty<'_>,
+    cast_to: Ty<'_>,
+) {
+    let literal_kind_name = if cast_from.is_integral() { "integer" } else { "float" };
+    span_lint_and_sugg(
+        cx,
+        UNNECESSARY_CAST,
+        expr.span,
+        &format!("casting {} literal to `{}` is unnecessary", literal_kind_name, cast_to),
+        "try",
+        format!("{}_{}", num, cast_to),
+        Applicability::MachineApplicable,
+    );
+}
+
 fn lint_numeric_casts<'tcx>(
     cx: &LateContext<'tcx>,
     expr: &Expr<'tcx>,

tests/ui/eq_op.rs

@@ -6,6 +6,7 @@
 #[allow(clippy::no_effect, unused_variables, clippy::unnecessary_operation, clippy::short_circuit_statement)]
 #[allow(clippy::nonminimal_bool)]
 #[allow(unused)]
+#[allow(clippy::unnecessary_cast)]
 fn main() {
     // simple values and comparisons
     1 == 1;

tests/ui/eq_op.stderr

@@ -1,5 +1,5 @@
 error: equal expressions as operands to `==`
-  --> $DIR/eq_op.rs:11:5
+  --> $DIR/eq_op.rs:12:5
    |
 LL |     1 == 1;
    |     ^^^^^^
@@ -7,157 +7,157 @@ LL |     1 == 1;
    = note: `-D clippy::eq-op` implied by `-D warnings`
 
 error: equal expressions as operands to `==`
-  --> $DIR/eq_op.rs:12:5
+  --> $DIR/eq_op.rs:13:5
    |
 LL |     "no" == "no";
    |     ^^^^^^^^^^^^
 
 error: equal expressions as operands to `!=`
-  --> $DIR/eq_op.rs:14:5
+  --> $DIR/eq_op.rs:15:5
    |
 LL |     false != false;
    |     ^^^^^^^^^^^^^^
 
 error: equal expressions as operands to `<`
-  --> $DIR/eq_op.rs:15:5
+  --> $DIR/eq_op.rs:16:5
    |
 LL |     1.5 < 1.5;
    |     ^^^^^^^^^
 
 error: equal expressions as operands to `>=`
-  --> $DIR/eq_op.rs:16:5
+  --> $DIR/eq_op.rs:17:5
    |
 LL |     1u64 >= 1u64;
    |     ^^^^^^^^^^^^
 
 error: equal expressions as operands to `&`
-  --> $DIR/eq_op.rs:19:5
+  --> $DIR/eq_op.rs:20:5
    |
 LL |     (1 as u64) & (1 as u64);
    |     ^^^^^^^^^^^^^^^^^^^^^^^
 
 error: equal expressions as operands to `^`
-  --> $DIR/eq_op.rs:20:5
+  --> $DIR/eq_op.rs:21:5
    |
 LL |     1 ^ ((((((1))))));
    |     ^^^^^^^^^^^^^^^^^
 
 error: equal expressions as operands to `<`
-  --> $DIR/eq_op.rs:23:5
+  --> $DIR/eq_op.rs:24:5
    |
 LL |     (-(2) < -(2));
    |     ^^^^^^^^^^^^^
 
 error: equal expressions as operands to `==`
-  --> $DIR/eq_op.rs:24:5
+  --> $DIR/eq_op.rs:25:5
    |
 LL |     ((1 + 1) & (1 + 1) == (1 + 1) & (1 + 1));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: equal expressions as operands to `&`
-  --> $DIR/eq_op.rs:24:6
+  --> $DIR/eq_op.rs:25:6
    |
 LL |     ((1 + 1) & (1 + 1) == (1 + 1) & (1 + 1));
    |      ^^^^^^^^^^^^^^^^^
 
 error: equal expressions as operands to `&`
-  --> $DIR/eq_op.rs:24:27
+  --> $DIR/eq_op.rs:25:27
    |
 LL |     ((1 + 1) & (1 + 1) == (1 + 1) & (1 + 1));
    |                           ^^^^^^^^^^^^^^^^^
 
 error: equal expressions as operands to `==`
-  --> $DIR/eq_op.rs:25:5
+  --> $DIR/eq_op.rs:26:5
    |
 LL |     (1 * 2) + (3 * 4) == 1 * 2 + 3 * 4;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: equal expressions as operands to `!=`
-  --> $DIR/eq_op.rs:28:5
+  --> $DIR/eq_op.rs:29:5
    |
 LL |     ([1] != [1]);
    |     ^^^^^^^^^^^^
 
 error: equal expressions as operands to `!=`
-  --> $DIR/eq_op.rs:29:5
+  --> $DIR/eq_op.rs:30:5
    |
 LL |     ((1, 2) != (1, 2));
    |     ^^^^^^^^^^^^^^^^^^
 
 error: equal expressions as operands to `==`
-  --> $DIR/eq_op.rs:33:5
+  --> $DIR/eq_op.rs:34:5
    |
 LL |     1 + 1 == 2;
    |     ^^^^^^^^^^
 
 error: equal expressions as operands to `==`
-  --> $DIR/eq_op.rs:34:5
+  --> $DIR/eq_op.rs:35:5
    |
 LL |     1 - 1 == 0;
    |     ^^^^^^^^^^
 
 error: equal expressions as operands to `-`
-  --> $DIR/eq_op.rs:34:5
+  --> $DIR/eq_op.rs:35:5
    |
 LL |     1 - 1 == 0;
    |     ^^^^^
 
 error: equal expressions as operands to `-`
-  --> $DIR/eq_op.rs:36:5
+  --> $DIR/eq_op.rs:37:5
    |
 LL |     1 - 1;
    |     ^^^^^
 
 error: equal expressions as operands to `/`
-  --> $DIR/eq_op.rs:37:5
+  --> $DIR/eq_op.rs:38:5
    |
 LL |     1 / 1;
    |     ^^^^^
 
 error: equal expressions as operands to `&&`
-  --> $DIR/eq_op.rs:38:5
+  --> $DIR/eq_op.rs:39:5
    |
 LL |     true && true;
    |     ^^^^^^^^^^^^
 
 error: equal expressions as operands to `||`
-  --> $DIR/eq_op.rs:40:5
+  --> $DIR/eq_op.rs:41:5
    |
 LL |     true || true;
    |     ^^^^^^^^^^^^
 
 error: equal expressions as operands to `&&`
-  --> $DIR/eq_op.rs:46:5
+  --> $DIR/eq_op.rs:47:5
    |
 LL |     a == b && b == a;
    |     ^^^^^^^^^^^^^^^^
 
 error: equal expressions as operands to `&&`
-  --> $DIR/eq_op.rs:47:5
+  --> $DIR/eq_op.rs:48:5
    |
 LL |     a != b && b != a;
    |     ^^^^^^^^^^^^^^^^
 
 error: equal expressions as operands to `&&`
-  --> $DIR/eq_op.rs:48:5
+  --> $DIR/eq_op.rs:49:5
    |
 LL |     a < b && b > a;
    |     ^^^^^^^^^^^^^^
 
 error: equal expressions as operands to `&&`
-  --> $DIR/eq_op.rs:49:5
+  --> $DIR/eq_op.rs:50:5
    |
 LL |     a <= b && b >= a;
    |     ^^^^^^^^^^^^^^^^
 
 error: equal expressions as operands to `==`
-  --> $DIR/eq_op.rs:52:5
+  --> $DIR/eq_op.rs:53:5
    |
 LL |     a == a;
    |     ^^^^^^
 
 error: equal expressions as operands to `/`
-  --> $DIR/eq_op.rs:62:20
+  --> $DIR/eq_op.rs:63:20
    |
 LL |     const D: u32 = A / A;
    |                    ^^^^^

tests/ui/unnecessary_cast_fixable.fixed

@@ -12,12 +12,19 @@ fn main() {
     #[rustfmt::skip]
     let v = vec!(1);
     &v as &[i32];
-    1.0 as f64;
-    1 as u64;
     0x10 as f32;
     0o10 as f32;
     0b10 as f32;
     0x11 as f64;
     0o11 as f64;
     0b11 as f64;
+
+    1_u32;
+    16_i32;
+    2_usize;
+
+    1.0_f64;
+    0.5_f32;
+
+    1.0 as u16;
 }

tests/ui/unnecessary_cast_fixable.rs

@@ -12,12 +12,19 @@ fn main() {
     #[rustfmt::skip]
     let v = vec!(1);
     &v as &[i32];
-    1.0 as f64;
-    1 as u64;
     0x10 as f32;
     0o10 as f32;
     0b10 as f32;
     0x11 as f64;
     0o11 as f64;
     0b11 as f64;
+
+    1 as u32;
+    0x10 as i32;
+    0b10 as usize;
+
+    1.0 as f64;
+    0.5 as f32;
+
+    1.0 as u16;
 }

tests/ui/unnecessary_cast_fixable.stderr

@@ -18,5 +18,35 @@ error: casting integer literal to `f64` is unnecessary
 LL |     100_i32 as f64;
    |     ^^^^^^^^^^^^^^ help: try: `100_f64`
 
-error: aborting due to 3 previous errors
+error: casting integer literal to `u32` is unnecessary
+  --> $DIR/unnecessary_cast_fixable.rs:22:5
+   |
+LL |     1 as u32;
+   |     ^^^^^^^^ help: try: `1_u32`
+
+error: casting integer literal to `i32` is unnecessary
+  --> $DIR/unnecessary_cast_fixable.rs:23:5
+   |
+LL |     0x10 as i32;
+   |     ^^^^^^^^^^^ help: try: `16_i32`
+
+error: casting integer literal to `usize` is unnecessary
+  --> $DIR/unnecessary_cast_fixable.rs:24:5
+   |
+LL |     0b10 as usize;
+   |     ^^^^^^^^^^^^^ help: try: `2_usize`
+
+error: casting float literal to `f64` is unnecessary
+  --> $DIR/unnecessary_cast_fixable.rs:26:5
+   |
+LL |     1.0 as f64;
+   |     ^^^^^^^^^^ help: try: `1.0_f64`
+
+error: casting float literal to `f32` is unnecessary
+  --> $DIR/unnecessary_cast_fixable.rs:27:5
+   |
+LL |     0.5 as f32;
+   |     ^^^^^^^^^^ help: try: `0.5_f32`
+
+error: aborting due to 8 previous errors