Handle empty where-clause better

src/test/ui/issues/issue-35668.stderr

@@ -6,7 +6,7 @@ LL |     a.iter().map(|a| a*a)
    |                      |
    |                      &T
    |
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
    |
 LL | fn func<'a, T>(a: &'a [T]) -> impl Iterator<Item=&'a T> where &T: Mul<&T> {
    |                                                         +++++++++++++++++

src/test/ui/partialeq_help.rs

@@ -2,6 +2,11 @@ fn foo<T: PartialEq>(a: &T, b: T) {
     a == b; //~ ERROR E0277
 }
 
+fn foo2<T: PartialEq>(a: &T, b: T) where {
+    a == b; //~ ERROR E0277
+}
+
 fn main() {
     foo(&1, 1);
+    foo2(&1, 1);
 }

src/test/ui/partialeq_help.stderr

@@ -5,11 +5,23 @@ LL |     a == b;
    |       ^^ no implementation for `&T == T`
    |
    = help: the trait `PartialEq<T>` is not implemented for `&T`
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
    |
 LL | fn foo<T: PartialEq>(a: &T, b: T) where &T: PartialEq<T> {
    |                                   ++++++++++++++++++++++
 
-error: aborting due to previous error
+error[E0277]: can't compare `&T` with `T`
+  --> $DIR/partialeq_help.rs:6:7
+   |
+LL |     a == b;
+   |       ^^ no implementation for `&T == T`
+   |
+   = help: the trait `PartialEq<T>` is not implemented for `&T`
+help: consider extending the `where` clause, but there might be an alternative better way to express this requirement
+   |
+LL | fn foo2<T: PartialEq>(a: &T, b: T) where &T: PartialEq<T> {
+   |                                          ++++++++++++++++
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

src/test/ui/rfc-2632-const-trait-impl/assoc-type.stderr

@@ -15,7 +15,7 @@ note: required by a bound in `Foo::Bar`
    |
 LL |     type Bar: ~const std::ops::Add;
    |               ^^^^^^^^^^^^^^^^^^^^ required by this bound in `Foo::Bar`
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
    |
 LL | impl const Foo for NonConstAdd where NonConstAdd: ~const Add {
    |                                +++++++++++++++++++++++++++++

src/test/ui/rfc-2632-const-trait-impl/default-method-body-is-const-body-checking.stderr

@@ -14,7 +14,7 @@ note: required by a bound in `foo`
    |
 LL | const fn foo<T>() where T: ~const Tr {}
    |                            ^^^^^^^^^ required by this bound in `foo`
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
    |
 LL | pub trait Foo where (): ~const Tr {
    |               +++++++++++++++++++

src/test/ui/specialization/default-associated-type-bound-2.stderr

@@ -20,7 +20,7 @@ note: required by a bound in `X::U`
    |
 LL |     type U: PartialEq<T>;
    |             ^^^^^^^^^^^^ required by this bound in `X::U`
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
    |
 LL | impl<B: 'static, T> X<B> for T where &'static B: PartialEq<B> {
    |                                ++++++++++++++++++++++++++++++

src/test/ui/suggestions/derive-macro-missing-bounds.stderr

@@ -13,7 +13,7 @@ help: consider annotating `a::Inner<T>` with `#[derive(Debug)]`
    |
 LL |     #[derive(Debug)]
    |
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
    |
 LL |     struct Outer<T>(Inner<T>) where a::Inner<T>: Debug;
    |                               ++++++++++++++++++++++++

src/test/ui/suggestions/invalid-bin-op.stderr

@@ -15,7 +15,7 @@ help: consider annotating `S<T>` with `#[derive(PartialEq)]`
    |
 LL | #[derive(PartialEq)]
    |
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
    |
 LL | pub fn foo<T>(s: S<T>, t: S<T>) where S<T>: PartialEq {
    |                                 +++++++++++++++++++++

src/test/ui/suggestions/suggest-change-mut.rs

@@ -2,7 +2,7 @@
 
 use std::io::{BufRead, BufReader, Read, Write};
 
-fn issue_81421<T: Read + Write>(mut stream: T) { //~ HELP consider introducing a `where` bound
+fn issue_81421<T: Read + Write>(mut stream: T) { //~ HELP consider introducing a `where` clause
     let initial_message = format!("Hello world");
     let mut buffer: Vec<u8> = Vec::new();
     let bytes_written = stream.write_all(initial_message.as_bytes());

src/test/ui/suggestions/suggest-change-mut.stderr

@@ -16,7 +16,7 @@ help: consider removing the leading `&`-reference
 LL -         let mut stream_reader = BufReader::new(&stream);
 LL +         let mut stream_reader = BufReader::new(stream);
    | 
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
    |
 LL | fn issue_81421<T: Read + Write>(mut stream: T) where &T: std::io::Read {
    |                                                +++++++++++++++++++++++

src/test/ui/traits/resolution-in-overloaded-op.stderr

@@ -6,7 +6,7 @@ LL |     a * b
    |     |
    |     &T
    |
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
    |
 LL | fn foo<T: MyMul<f64, f64>>(a: &T, b: f64) -> f64 where &T: Mul<f64> {
    |                                                  ++++++++++++++++++

src/test/ui/traits/suggest-where-clause.stderr

@@ -49,7 +49,7 @@ error[E0277]: the trait bound `u64: From<T>` is not satisfied
 LL |     <u64 as From<T>>::from;
    |     ^^^^^^^^^^^^^^^^^^^^^^ the trait `From<T>` is not implemented for `u64`
    |
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
    |
 LL | fn check<T: Iterator, U: ?Sized>() where u64: From<T> {
    |                                    ++++++++++++++++++
@@ -60,7 +60,7 @@ error[E0277]: the trait bound `u64: From<<T as Iterator>::Item>` is not satisfie
 LL |     <u64 as From<<T as Iterator>::Item>>::from;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `From<<T as Iterator>::Item>` is not implemented for `u64`
    |
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
    |
 LL | fn check<T: Iterator, U: ?Sized>() where u64: From<<T as Iterator>::Item> {
    |                                    ++++++++++++++++++++++++++++++++++++++

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn.stderr

@@ -5,7 +5,7 @@ LL |     (a, a)
    |         ^ the trait `From<&A>` is not implemented for `&'static B`
    |
    = note: required because of the requirements on the impl of `Into<&'static B>` for `&A`
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
    |
 LL | fn f<A, B: 'static>(a: &'static A, b: B) -> (X<A, B>, X<B, A>) where &'static B: From<&A> {
    |                                                                ++++++++++++++++++++++++++