Provide RHS type hint when reporting operator error

Author: compiler-errors

compiler/rustc_hir_typeck/src/op.rs

@@ -776,6 +776,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 Ok(method)
             }
             None => {
+                // This path may do some inference, so make sure we've really
+                // doomed compilation so as to not accidentally stabilize new
+                // inference or something here...
+                self.tcx.sess.delay_span_bug(span, "this path really should be doomed...");
+                // Guide inference for the RHS expression if it's provided --
+                // this will allow us to better error reporting, at the expense
+                // of making some error messages a bit more specific.
+                if let Some((rhs_expr, rhs_ty)) = opt_rhs
+                    && rhs_ty.is_ty_var()
+                {
+                    self.check_expr_coercible_to_type(rhs_expr, rhs_ty, None);
+                }
+
                 let (obligation, _) =
                     self.obligation_for_method(cause, trait_did, lhs_ty, Some(input_types));
                 // FIXME: This should potentially just add the obligation to the `FnCtxt`

tests/ui/binop/eq-arr.rs

@@ -0,0 +1,7 @@
+fn main() {
+    struct X;
+    //~^ HELP consider annotating `X` with `#[derive(PartialEq)]`
+    let xs = [X, X, X];
+    let eq = xs == [X, X, X];
+    //~^ ERROR binary operation `==` cannot be applied to type `[X; 3]`
+}

tests/ui/binop/eq-arr.stderr

@@ -0,0 +1,22 @@
+error[E0369]: binary operation `==` cannot be applied to type `[X; 3]`
+  --> $DIR/eq-arr.rs:5:17
+   |
+LL |     let eq = xs == [X, X, X];
+   |              -- ^^ --------- [X; 3]
+   |              |
+   |              [X; 3]
+   |
+note: an implementation of `PartialEq` might be missing for `X`
+  --> $DIR/eq-arr.rs:2:5
+   |
+LL |     struct X;
+   |     ^^^^^^^^ must implement `PartialEq`
+help: consider annotating `X` with `#[derive(PartialEq)]`
+   |
+LL +     #[derive(PartialEq)]
+LL |     struct X;
+   |
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0369`.

tests/ui/binop/eq-vec.rs

@@ -0,0 +1,13 @@
+fn main() {
+    #[derive(Debug)]
+    enum Foo {
+        //~^ HELP consider annotating `Foo` with `#[derive(PartialEq)]`
+        Bar,
+        Qux,
+    }
+
+    let vec1 = vec![Foo::Bar, Foo::Qux];
+    let vec2 = vec![Foo::Bar, Foo::Qux];
+    assert_eq!(vec1, vec2);
+    //~^ ERROR binary operation `==` cannot be applied to type `Vec<Foo>`
+}

tests/ui/binop/eq-vec.stderr

@@ -0,0 +1,24 @@
+error[E0369]: binary operation `==` cannot be applied to type `Vec<Foo>`
+  --> $DIR/eq-vec.rs:11:5
+   |
+LL |     assert_eq!(vec1, vec2);
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |     |
+   |     Vec<Foo>
+   |     Vec<Foo>
+   |
+note: an implementation of `PartialEq` might be missing for `Foo`
+  --> $DIR/eq-vec.rs:3:5
+   |
+LL |     enum Foo {
+   |     ^^^^^^^^ must implement `PartialEq`
+   = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Foo` with `#[derive(PartialEq)]`
+   |
+LL +     #[derive(PartialEq)]
+LL |     enum Foo {
+   |
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0369`.

tests/ui/binop/issue-28837.stderr

@@ -6,11 +6,11 @@ LL |     a + a;
    |     |
    |     A
    |
-note: an implementation of `Add<_>` might be missing for `A`
+note: an implementation of `Add` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `Add<_>`
+   | ^^^^^^^^ must implement `Add`
 note: the trait `Add` must be implemented
   --> $SRC_DIR/core/src/ops/arith.rs:LL:COL
 
@@ -22,11 +22,11 @@ LL |     a - a;
    |     |
    |     A
    |
-note: an implementation of `Sub<_>` might be missing for `A`
+note: an implementation of `Sub` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `Sub<_>`
+   | ^^^^^^^^ must implement `Sub`
 note: the trait `Sub` must be implemented
   --> $SRC_DIR/core/src/ops/arith.rs:LL:COL
 
@@ -38,11 +38,11 @@ LL |     a * a;
    |     |
    |     A
    |
-note: an implementation of `Mul<_>` might be missing for `A`
+note: an implementation of `Mul` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `Mul<_>`
+   | ^^^^^^^^ must implement `Mul`
 note: the trait `Mul` must be implemented
   --> $SRC_DIR/core/src/ops/arith.rs:LL:COL
 
@@ -54,11 +54,11 @@ LL |     a / a;
    |     |
    |     A
    |
-note: an implementation of `Div<_>` might be missing for `A`
+note: an implementation of `Div` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `Div<_>`
+   | ^^^^^^^^ must implement `Div`
 note: the trait `Div` must be implemented
   --> $SRC_DIR/core/src/ops/arith.rs:LL:COL
 
@@ -70,11 +70,11 @@ LL |     a % a;
    |     |
    |     A
    |
-note: an implementation of `Rem<_>` might be missing for `A`
+note: an implementation of `Rem` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `Rem<_>`
+   | ^^^^^^^^ must implement `Rem`
 note: the trait `Rem` must be implemented
   --> $SRC_DIR/core/src/ops/arith.rs:LL:COL
 
@@ -86,11 +86,11 @@ LL |     a & a;
    |     |
    |     A
    |
-note: an implementation of `BitAnd<_>` might be missing for `A`
+note: an implementation of `BitAnd` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `BitAnd<_>`
+   | ^^^^^^^^ must implement `BitAnd`
 note: the trait `BitAnd` must be implemented
   --> $SRC_DIR/core/src/ops/bit.rs:LL:COL
 
@@ -102,11 +102,11 @@ LL |     a | a;
    |     |
    |     A
    |
-note: an implementation of `BitOr<_>` might be missing for `A`
+note: an implementation of `BitOr` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `BitOr<_>`
+   | ^^^^^^^^ must implement `BitOr`
 note: the trait `BitOr` must be implemented
   --> $SRC_DIR/core/src/ops/bit.rs:LL:COL
 
@@ -118,11 +118,11 @@ LL |     a << a;
    |     |
    |     A
    |
-note: an implementation of `Shl<_>` might be missing for `A`
+note: an implementation of `Shl` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `Shl<_>`
+   | ^^^^^^^^ must implement `Shl`
 note: the trait `Shl` must be implemented
   --> $SRC_DIR/core/src/ops/bit.rs:LL:COL
 
@@ -134,11 +134,11 @@ LL |     a >> a;
    |     |
    |     A
    |
-note: an implementation of `Shr<_>` might be missing for `A`
+note: an implementation of `Shr` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `Shr<_>`
+   | ^^^^^^^^ must implement `Shr`
 note: the trait `Shr` must be implemented
   --> $SRC_DIR/core/src/ops/bit.rs:LL:COL
 
@@ -150,11 +150,11 @@ LL |     a == a;
    |     |
    |     A
    |
-note: an implementation of `PartialEq<_>` might be missing for `A`
+note: an implementation of `PartialEq` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `PartialEq<_>`
+   | ^^^^^^^^ must implement `PartialEq`
 help: consider annotating `A` with `#[derive(PartialEq)]`
    |
 LL + #[derive(PartialEq)]
@@ -169,11 +169,11 @@ LL |     a != a;
    |     |
    |     A
    |
-note: an implementation of `PartialEq<_>` might be missing for `A`
+note: an implementation of `PartialEq` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `PartialEq<_>`
+   | ^^^^^^^^ must implement `PartialEq`
 help: consider annotating `A` with `#[derive(PartialEq)]`
    |
 LL + #[derive(PartialEq)]
@@ -188,11 +188,11 @@ LL |     a < a;
    |     |
    |     A
    |
-note: an implementation of `PartialOrd<_>` might be missing for `A`
+note: an implementation of `PartialOrd` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `PartialOrd<_>`
+   | ^^^^^^^^ must implement `PartialOrd`
 help: consider annotating `A` with `#[derive(PartialEq, PartialOrd)]`
    |
 LL + #[derive(PartialEq, PartialOrd)]
@@ -207,11 +207,11 @@ LL |     a <= a;
    |     |
    |     A
    |
-note: an implementation of `PartialOrd<_>` might be missing for `A`
+note: an implementation of `PartialOrd` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `PartialOrd<_>`
+   | ^^^^^^^^ must implement `PartialOrd`
 help: consider annotating `A` with `#[derive(PartialEq, PartialOrd)]`
    |
 LL + #[derive(PartialEq, PartialOrd)]
@@ -226,11 +226,11 @@ LL |     a > a;
    |     |
    |     A
    |
-note: an implementation of `PartialOrd<_>` might be missing for `A`
+note: an implementation of `PartialOrd` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `PartialOrd<_>`
+   | ^^^^^^^^ must implement `PartialOrd`
 help: consider annotating `A` with `#[derive(PartialEq, PartialOrd)]`
    |
 LL + #[derive(PartialEq, PartialOrd)]
@@ -245,11 +245,11 @@ LL |     a >= a;
    |     |
    |     A
    |
-note: an implementation of `PartialOrd<_>` might be missing for `A`
+note: an implementation of `PartialOrd` might be missing for `A`
   --> $DIR/issue-28837.rs:1:1
    |
 LL | struct A;
-   | ^^^^^^^^ must implement `PartialOrd<_>`
+   | ^^^^^^^^ must implement `PartialOrd`
 help: consider annotating `A` with `#[derive(PartialEq, PartialOrd)]`
    |
 LL + #[derive(PartialEq, PartialOrd)]

tests/ui/binop/issue-3820.stderr

@@ -6,11 +6,11 @@ LL |     let w = u * 3;
    |             |
    |             Thing
    |
-note: an implementation of `Mul<_>` might be missing for `Thing`
+note: an implementation of `Mul<{integer}>` might be missing for `Thing`
   --> $DIR/issue-3820.rs:1:1
    |
 LL | struct Thing {
-   | ^^^^^^^^^^^^ must implement `Mul<_>`
+   | ^^^^^^^^^^^^ must implement `Mul<{integer}>`
 note: the trait `Mul` must be implemented
   --> $SRC_DIR/core/src/ops/arith.rs:LL:COL
 

tests/ui/derives/derives-span-PartialEq-enum-struct-variant.stderr

@@ -7,11 +7,11 @@ LL | #[derive(PartialEq)]
 LL |      x: Error
    |      ^^^^^^^^
    |
-note: an implementation of `PartialEq<_>` might be missing for `Error`
+note: an implementation of `PartialEq` might be missing for `Error`
   --> $DIR/derives-span-PartialEq-enum-struct-variant.rs:4:1
    |
 LL | struct Error;
-   | ^^^^^^^^^^^^ must implement `PartialEq<_>`
+   | ^^^^^^^^^^^^ must implement `PartialEq`
    = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider annotating `Error` with `#[derive(PartialEq)]`
    |

tests/ui/derives/derives-span-PartialEq-enum.stderr

@@ -7,11 +7,11 @@ LL | #[derive(PartialEq)]
 LL |      Error
    |      ^^^^^
    |
-note: an implementation of `PartialEq<_>` might be missing for `Error`
+note: an implementation of `PartialEq` might be missing for `Error`
   --> $DIR/derives-span-PartialEq-enum.rs:4:1
    |
 LL | struct Error;
-   | ^^^^^^^^^^^^ must implement `PartialEq<_>`
+   | ^^^^^^^^^^^^ must implement `PartialEq`
    = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider annotating `Error` with `#[derive(PartialEq)]`
    |

tests/ui/derives/derives-span-PartialEq-struct.stderr

@@ -7,11 +7,11 @@ LL | struct Struct {
 LL |     x: Error
    |     ^^^^^^^^
    |
-note: an implementation of `PartialEq<_>` might be missing for `Error`
+note: an implementation of `PartialEq` might be missing for `Error`
   --> $DIR/derives-span-PartialEq-struct.rs:4:1
    |
 LL | struct Error;
-   | ^^^^^^^^^^^^ must implement `PartialEq<_>`
+   | ^^^^^^^^^^^^ must implement `PartialEq`
    = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider annotating `Error` with `#[derive(PartialEq)]`
    |