Auto merge of #28933 - fhahn:issue-28837-partialeq-note, r=alexcrichton

this PR adds notes for missing `PartialEq` and `PartialOrd`. I've added a test case but it seems like `NOTE` is ignored by the test runner.

#28837

2 files changed, 81 insertions, 0 deletions

diff --git a/src/librustc_typeck/check/op.rs b/src/librustc_typeck/check/op.rs
index 7be61327f81..0c65f68f02e 100644
--- a/src/librustc_typeck/check/op.rs
+++ b/src/librustc_typeck/check/op.rs
@@ -191,6 +191,27 @@ fn check_overloaded_binop<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                               "binary operation `{}` cannot be applied to type `{}`",
                               hir_util::binop_to_string(op.node),
                               lhs_ty);
+                    let missing_trait = match op.node {
+                        hir::BiAdd    => Some("std::ops::Add"),
+                        hir::BiSub    => Some("std::ops::Sub"),
+                        hir::BiMul    => Some("std::ops::Mul"),
+                        hir::BiDiv    => Some("std::ops::Div"),
+                        hir::BiRem    => Some("std::ops::Rem"),
+                        hir::BiBitAnd => Some("std::ops::BitAnd"),
+                        hir::BiBitOr  => Some("std::ops::BitOr"),
+                        hir::BiShl    => Some("std::ops::Shl"),
+                        hir::BiShr    => Some("std::ops::Shr"),
+                        hir::BiEq | hir::BiNe => Some("std::cmp::PartialEq"),
+                        hir::BiLt | hir::BiLe | hir::BiGt | hir::BiGe =>
+                            Some("std::cmp::PartialOrd"),
+                        _             => None
+                    };
+
+                    if let Some(missing_trait) = missing_trait {
+                        span_note!(fcx.tcx().sess, lhs_expr.span,
+                                   "an implementation of `{}` might be missing for `{}`",
+                                    missing_trait, lhs_ty);
+                    }
                 }
             }
             fcx.tcx().types.err
diff --git a/src/test/compile-fail/issue-28837.rs b/src/test/compile-fail/issue-28837.rs
new file mode 100644
index 00000000000..c7cf63bf2c4
--- /dev/null
+++ b/src/test/compile-fail/issue-28837.rs
@@ -0,0 +1,60 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct A;
+
+fn main() {
+    let a = A;
+
+    a + a; //~ ERROR binary operation `+` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::ops::Add` might be missing for `A`
+
+    a - a; //~ ERROR binary operation `-` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::ops::Sub` might be missing for `A`
+
+    a * a; //~ ERROR binary operation `*` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::ops::Mul` might be missing for `A`
+
+    a / a; //~ ERROR binary operation `/` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::ops::Div` might be missing for `A`
+
+    a % a; //~ ERROR binary operation `%` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::ops::Rem` might be missing for `A`
+
+    a & a; //~ ERROR binary operation `&` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::ops::BitAnd` might be missing for `A`
+
+    a | a; //~ ERROR binary operation `|` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::ops::BitOr` might be missing for `A`
+
+    a << a; //~ ERROR binary operation `<<` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::ops::Shl` might be missing for `A`
+
+    a >> a; //~ ERROR binary operation `>>` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::ops::Shr` might be missing for `A`
+
+    a == a; //~ ERROR binary operation `==` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::cmp::PartialEq` might be missing for `A`
+
+    a != a; //~ ERROR binary operation `!=` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::cmp::PartialEq` might be missing for `A`
+
+    a < a; //~ ERROR binary operation `<` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::cmp::PartialOrd` might be missing for `A`
+
+    a <= a; //~ ERROR binary operation `<=` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::cmp::PartialOrd` might be missing for `A`
+
+    a > a; //~ ERROR binary operation `>` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::cmp::PartialOrd` might be missing for `A`
+
+    a >= a; //~ ERROR binary operation `>=` cannot be applied to type `A`
+    //~^ NOTE an implementation of `std::cmp::PartialOrd` might be missing for `A`
+}