Merge #3331

3331: Disable arithmetic lints in constant items r=oli-obk a=pengowen123

Currently this will not catch cases in associated constants. I'm not sure whether checking spans is the best way to solve this issue, but I don't think it will cause any problems.
Fixes #1858

Co-authored-by: Owen Sanchez <pengowen816@gmail.com>

clippy_lints/src/arithmetic.rs

@@ -51,7 +51,9 @@ declare_clippy_lint! {
 
 #[derive(Copy, Clone, Default)]
 pub struct Arithmetic {
-    span: Option<Span>,
+    expr_span: Option<Span>,
+    /// This field is used to check whether expressions are constants, such as in enum discriminants and consts
+    const_span: Option<Span>,
 }
 
 impl LintPass for Arithmetic {
@@ -62,9 +64,15 @@ impl LintPass for Arithmetic {
 
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Arithmetic {
     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
-        if self.span.is_some() {
+        if self.expr_span.is_some() {
             return;
         }
+
+        if let Some(span) = self.const_span {
+            if span.contains(expr.span) {
+                return;
+            }
+        }
         match expr.node {
             hir::ExprKind::Binary(ref op, ref l, ref r) => {
                 match op.node {
@@ -86,20 +94,20 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Arithmetic {
                 let (l_ty, r_ty) = (cx.tables.expr_ty(l), cx.tables.expr_ty(r));
                 if l_ty.is_integral() && r_ty.is_integral() {
                     span_lint(cx, INTEGER_ARITHMETIC, expr.span, "integer arithmetic detected");
-                    self.span = Some(expr.span);
+                    self.expr_span = Some(expr.span);
                 } else if l_ty.is_floating_point() && r_ty.is_floating_point() {
                     span_lint(cx, FLOAT_ARITHMETIC, expr.span, "floating-point arithmetic detected");
-                    self.span = Some(expr.span);
+                    self.expr_span = Some(expr.span);
                 }
             },
             hir::ExprKind::Unary(hir::UnOp::UnNeg, ref arg) => {
                 let ty = cx.tables.expr_ty(arg);
                 if ty.is_integral() {
                     span_lint(cx, INTEGER_ARITHMETIC, expr.span, "integer arithmetic detected");
-                    self.span = Some(expr.span);
+                    self.expr_span = Some(expr.span);
                 } else if ty.is_floating_point() {
                     span_lint(cx, FLOAT_ARITHMETIC, expr.span, "floating-point arithmetic detected");
-                    self.span = Some(expr.span);
+                    self.expr_span = Some(expr.span);
                 }
             },
             _ => (),
@@ -107,8 +115,39 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Arithmetic {
     }
 
     fn check_expr_post(&mut self, _: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
-        if Some(expr.span) == self.span {
-            self.span = None;
+        if Some(expr.span) == self.expr_span {
+            self.expr_span = None;
         }
     }
+
+    fn check_body(&mut self, cx: &LateContext<'_, '_>, body: &hir::Body) {
+        let body_owner = cx.tcx.hir.body_owner(body.id());
+
+        match cx.tcx.hir.body_owner_kind(body_owner) {
+            hir::BodyOwnerKind::Static(_)
+            | hir::BodyOwnerKind::Const => {
+                let body_span = cx.tcx.hir.span(body_owner);
+
+                if let Some(span) = self.const_span {
+                    if span.contains(body_span) {
+                        return;
+                    }
+                }
+                self.const_span = Some(body_span);
+            }
+            hir::BodyOwnerKind::Fn => (),
+        }
+    }
+
+    fn check_body_post(&mut self, cx: &LateContext<'_, '_>, body: &hir::Body) {
+        let body_owner = cx.tcx.hir.body_owner(body.id());
+        let body_span = cx.tcx.hir.span(body_owner);
+
+        if let Some(span) = self.const_span {
+            if span.contains(body_span) {
+                return;
+            }
+        }
+        self.const_span = None;
+    }
 }

tests/ui/arithmetic.rs

@@ -37,4 +37,36 @@ fn main() {
     f / 2.0;
     f - 2.0 * 4.2;
     -f;
+
+    // No errors for the following items because they are constant expressions
+    enum Foo {
+        Bar = -2,
+    }
+    struct Baz([i32; 1 + 1]);
+    union Qux {
+        field: [i32; 1 + 1],
+    }
+    type Alias = [i32; 1 + 1];
+
+    const FOO: i32 = -2;
+    static BAR: i32 = -2;
+
+    let _: [i32; 1 + 1] = [0, 0];
+
+    let _: [i32; 1 + 1] = {
+        let a: [i32; 1 + 1] = [0, 0];
+        a
+    };
+
+    trait Trait {
+        const ASSOC: i32 = 1 + 1;
+    }
+
+    impl Trait for Foo {
+        const ASSOC: i32 = {
+            let _: [i32; 1 + 1];
+            fn foo() {}
+            1 + 1
+        };
+    }
 }