Rollup merge of #107389 - zvavybir:master, r=estebank

Fixing confusion between mod and remainder

Like many programming languages, rust too confuses remainder and modulus.  The `%` operator and the associated `Rem` trait is (as the trait name suggests) the remainder, but since most people are linguistically more familiar with the modulus the documentation sometimes claims otherwise.  This PR tries to fix this problem in rustc.

Author: matthiaskrgr

compiler/rustc_hir_typeck/src/op.rs

@@ -335,7 +335,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 format!("cannot divide `{lhs_ty}` by `{rhs_ty}`")
                             }
                             hir::BinOpKind::Rem => {
-                                format!("cannot mod `{lhs_ty}` by `{rhs_ty}`")
+                                format!(
+                                    "cannot calculate the remainder of `{lhs_ty}` divided by `{rhs_ty}`"
+                                )
                             }
                             hir::BinOpKind::BitAnd => {
                                 format!("no implementation for `{lhs_ty} & {rhs_ty}`")

library/core/src/ops/arith.rs

@@ -545,7 +545,7 @@ div_impl_float! { f32 f64 }
 #[lang = "rem"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented(
-    message = "cannot mod `{Self}` by `{Rhs}`",
+    message = "cannot calculate the remainder of `{Self}` divided by `{Rhs}`",
     label = "no implementation for `{Self} % {Rhs}`"
 )]
 #[doc(alias = "%")]
@@ -981,7 +981,7 @@ div_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 #[lang = "rem_assign"]
 #[stable(feature = "op_assign_traits", since = "1.8.0")]
 #[rustc_on_unimplemented(
-    message = "cannot mod-assign `{Self}` by `{Rhs}``",
+    message = "cannot calculate and assign the remainder of `{Self}` divided by `{Rhs}`",
     label = "no implementation for `{Self} %= {Rhs}`"
 )]
 #[doc(alias = "%")]

tests/ui/binop/binary-op-on-double-ref.fixed

@@ -3,7 +3,7 @@ fn main() {
     let v = vec![1, 2, 3, 4, 5, 6, 7, 8, 9];
     let vr = v.iter().filter(|x| {
         *x % 2 == 0
-        //~^ ERROR cannot mod `&&{integer}` by `{integer}`
+        //~^ ERROR cannot calculate the remainder of `&&{integer}` divided by `{integer}`
     });
     println!("{:?}", vr);
 }

tests/ui/binop/binary-op-on-double-ref.rs

@@ -3,7 +3,7 @@ fn main() {
     let v = vec![1, 2, 3, 4, 5, 6, 7, 8, 9];
     let vr = v.iter().filter(|x| {
         x % 2 == 0
-        //~^ ERROR cannot mod `&&{integer}` by `{integer}`
+        //~^ ERROR cannot calculate the remainder of `&&{integer}` divided by `{integer}`
     });
     println!("{:?}", vr);
 }

tests/ui/binop/binary-op-on-double-ref.stderr

@@ -1,4 +1,4 @@
-error[E0369]: cannot mod `&&{integer}` by `{integer}`
+error[E0369]: cannot calculate the remainder of `&&{integer}` divided by `{integer}`
   --> $DIR/binary-op-on-double-ref.rs:5:11
    |
 LL |         x % 2 == 0

tests/ui/binop/issue-28837.rs

@@ -11,7 +11,7 @@ fn main() {
 
     a / a; //~ ERROR cannot divide `A` by `A`
 
-    a % a; //~ ERROR cannot mod `A` by `A`
+    a % a; //~ ERROR cannot calculate the remainder of `A` divided by `A`
 
     a & a; //~ ERROR no implementation for `A & A`
 

tests/ui/binop/issue-28837.stderr

@@ -62,7 +62,7 @@ LL | struct A;
 note: the trait `Div` must be implemented
   --> $SRC_DIR/core/src/ops/arith.rs:LL:COL
 
-error[E0369]: cannot mod `A` by `A`
+error[E0369]: cannot calculate the remainder of `A` divided by `A`
   --> $DIR/issue-28837.rs:14:7
    |
 LL |     a % a;