Add lint to detect conversions between degrees and radians

Author: krishna-veerareddy

README.md

@@ -6,7 +6,7 @@
 
 A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
 
-[There are 340 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are 341 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
 
 We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
 

clippy_lints/src/floating_point_arithmetic.rs

@@ -126,17 +126,17 @@ fn check_ln1p(cx: &LateContext<'_, '_>, expr: &Expr, args: &HirVec<Expr>) {
 // casted without loss
 #[allow(clippy::cast_possible_truncation)]
 fn get_integer_from_float_constant(value: &Constant) -> Option<i64> {
-    match value {
-        F32(num) if (num.trunc() - num).abs() <= std::f32::EPSILON => {
-            if *num > -16_777_217.0 && *num < 16_777_217.0 {
-                Some(num.round() as i64)
+    match *value {
+        F32(num) if num.trunc() - num == 0.0 => {
+            if num > -16_777_217.0 && num < 16_777_217.0 {
+                Some(num as i64)
             } else {
                 None
             }
         },
-        F64(num) if (num.trunc() - num).abs() <= std::f64::EPSILON => {
-            if *num > -9_007_199_254_740_993.0 && *num < 9_007_199_254_740_993.0 {
-                Some(num.round() as i64)
+        F64(num) if num.trunc() - num == 0.0 => {
+            if num > -9_007_199_254_740_993.0 && num < 9_007_199_254_740_993.0 {
+                Some(num as i64)
             } else {
                 None
             }
@@ -313,6 +313,41 @@ fn check_log_division(cx: &LateContext<'_, '_>, expr: &Expr) {
     }
 }
 
+fn check_conversion_between_deg_and_rad(cx: &LateContext<'_, '_>, expr: &'_ Expr) {
+    if_chain! {
+        if let ExprKind::Binary(op, ref lhs, ref rhs) = expr.kind;
+        if op.node == BinOpKind::Mul;
+        if cx.tables.expr_ty(lhs).is_floating_point();
+        then {
+            let (recv, value) = if let Some((value, _)) = constant(cx, cx.tables, lhs) {
+                (rhs, value)
+            } else if let Some((value, _)) = constant(cx, cx.tables, rhs) {
+                (lhs, value)
+            } else {
+                return;
+            };
+
+            let unit = if F32(f32_consts::PI / 180.0) == value || F64(f64_consts::PI / 180.0) == value {
+                "radians"
+            } else if F32(180.0 / f32_consts::PI) == value || F64(180.0 / f64_consts::PI) == value {
+                "degrees"
+            } else {
+                return;
+            };
+
+            span_lint_and_sugg(
+                cx,
+                FLOATING_POINT_IMPROVEMENTS,
+                expr.span,
+                "conversions between degrees and radians can be expressed more succinctly",
+                "consider using",
+                format!("{}.to_{}()", sugg::Sugg::hir(cx, recv, "..").maybe_par(), unit),
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+}
+
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FloatingPointArithmetic {
     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
         if let ExprKind::MethodCall(ref path, _, args) = &expr.kind {
@@ -329,6 +364,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FloatingPointArithmetic {
         } else {
             check_expm1(cx, expr);
             check_log_division(cx, expr);
+            check_conversion_between_deg_and_rad(cx, expr);
         }
     }
 }

src/lintlist/mod.rs

@@ -6,7 +6,7 @@ pub use lint::Lint;
 pub use lint::LINT_LEVELS;
 
 // begin lint list, do not remove this comment, it’s used in `update_lints`
-pub const ALL_LINTS: [Lint; 340] = [
+pub const ALL_LINTS: [Lint; 341] = [
     Lint {
         name: "absurd_extreme_comparisons",
         group: "correctness",

tests/ui/floating_point_deg_rad_conversion.rs

@@ -0,0 +1,16 @@
+#![warn(clippy::floating_point_improvements)]
+
+fn main() {
+    let x = 2f32;
+    let _ = x * (std::f32::consts::PI / 180.0);
+    let _ = (std::f32::consts::PI / 180.0) * x;
+    let _ = -x * (std::f32::consts::PI / 180.0);
+    let _ = x * (180.0 / std::f32::consts::PI);
+    let _ = (180.0 / std::f32::consts::PI) * x;
+
+    let x = 2f64;
+    let _ = x * (std::f64::consts::PI / 180.0);
+    let _ = (std::f64::consts::PI / 180.0) * x;
+    let _ = x * (180.0 / std::f64::consts::PI);
+    let _ = (180.0 / std::f64::consts::PI) * x;
+}

tests/ui/floating_point_deg_rad_conversion.stderr

@@ -0,0 +1,58 @@
+error: conversions between degrees and radians can be expressed more succinctly
+  --> $DIR/floating_point_deg_rad_conversion.rs:5:13
+   |
+LL |     let _ = x * (std::f32::consts::PI / 180.0);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.to_radians()`
+   |
+   = note: `-D clippy::floating-point-improvements` implied by `-D warnings`
+
+error: conversions between degrees and radians can be expressed more succinctly
+  --> $DIR/floating_point_deg_rad_conversion.rs:6:13
+   |
+LL |     let _ = (std::f32::consts::PI / 180.0) * x;
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.to_radians()`
+
+error: conversions between degrees and radians can be expressed more succinctly
+  --> $DIR/floating_point_deg_rad_conversion.rs:7:13
+   |
+LL |     let _ = -x * (std::f32::consts::PI / 180.0);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `(-x).to_radians()`
+
+error: conversions between degrees and radians can be expressed more succinctly
+  --> $DIR/floating_point_deg_rad_conversion.rs:8:13
+   |
+LL |     let _ = x * (180.0 / std::f32::consts::PI);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.to_degrees()`
+
+error: conversions between degrees and radians can be expressed more succinctly
+  --> $DIR/floating_point_deg_rad_conversion.rs:9:13
+   |
+LL |     let _ = (180.0 / std::f32::consts::PI) * x;
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.to_degrees()`
+
+error: conversions between degrees and radians can be expressed more succinctly
+  --> $DIR/floating_point_deg_rad_conversion.rs:12:13
+   |
+LL |     let _ = x * (std::f64::consts::PI / 180.0);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.to_radians()`
+
+error: conversions between degrees and radians can be expressed more succinctly
+  --> $DIR/floating_point_deg_rad_conversion.rs:13:13
+   |
+LL |     let _ = (std::f64::consts::PI / 180.0) * x;
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.to_radians()`
+
+error: conversions between degrees and radians can be expressed more succinctly
+  --> $DIR/floating_point_deg_rad_conversion.rs:14:13
+   |
+LL |     let _ = x * (180.0 / std::f64::consts::PI);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.to_degrees()`
+
+error: conversions between degrees and radians can be expressed more succinctly
+  --> $DIR/floating_point_deg_rad_conversion.rs:15:13
+   |
+LL |     let _ = (180.0 / std::f64::consts::PI) * x;
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.to_degrees()`
+
+error: aborting due to 9 previous errors
+