Specific labels when referring to "expected" and "found" types

src/librustc/infer/error_reporting/mod.rs

@@ -1163,8 +1163,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             Some(values) => {
                 let (is_simple_error, exp_found) = match values {
                     ValuePairs::Types(exp_found) => {
-                        let is_simple_err =
-                            exp_found.expected.is_primitive() && exp_found.found.is_primitive();
+                        let is_simple_err = exp_found.expected.is_simple_text()
+                            && exp_found.found.is_simple_text();
 
                         (is_simple_err, Some(exp_found))
                     }
@@ -1197,40 +1197,61 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         };
 
         if let Some((expected, found)) = expected_found {
-            match (terr, is_simple_error, expected == found) {
-                (&TypeError::Sorts(ref values), false, true) => {
-                    let sort_string = | a_type: Ty<'tcx> |
-                        if let ty::Opaque(def_id, _) = a_type.kind {
-                            format!(" (opaque type at {})", self.tcx.sess.source_map()
-                                .mk_substr_filename(self.tcx.def_span(def_id)))
-                        } else {
-                            format!(" ({})", a_type.sort_string(self.tcx))
-                        };
-                    diag.note_expected_found_extra(
-                        &"type",
-                        expected,
-                        found,
-                        &sort_string(values.expected),
-                        &sort_string(values.found),
-                    );
+            let expected_label = exp_found.map_or("type".into(), |ef| ef.expected.prefix_string());
+            let found_label = exp_found.map_or("type".into(), |ef| ef.found.prefix_string());
+            match (&terr, expected == found) {
+                (TypeError::Sorts(values), extra) => {
+                    let sort_string = |ty: Ty<'tcx>| match (extra, &ty.kind) {
+                        (true, ty::Opaque(def_id, _)) => format!(
+                            " (opaque type at {})",
+                            self.tcx.sess.source_map()
+                                .mk_substr_filename(self.tcx.def_span(*def_id)),
+                        ),
+                        (true, _) => format!(" ({})", ty.sort_string(self.tcx)),
+                        (false, _) => "".to_string(),
+                    };
+                    if !(values.expected.is_simple_text() && values.found.is_simple_text()) || (
+                        exp_found.map_or(false, |ef| {
+                            // This happens when the type error is a subset of the expectation,
+                            // like when you have two references but one is `usize` and the other
+                            // is `f32`. In those cases we still want to show the `note`. If the
+                            // value from `ef` is `Infer(_)`, then we ignore it.
+                            if !ef.expected.is_ty_infer() {
+                                ef.expected != values.expected
+                            } else if !ef.found.is_ty_infer() {
+                                ef.found != values.found
+                            } else {
+                                false
+                            }
+                        })
+                    ) {
+                        diag.note_expected_found_extra(
+                            &expected_label,
+                            expected,
+                            &found_label,
+                            found,
+                            &sort_string(values.expected),
+                            &sort_string(values.found),
+                        );
+                    }
                 }
-                (TypeError::ObjectUnsafeCoercion(_), ..) => {
+                (TypeError::ObjectUnsafeCoercion(_), _) => {
                     diag.note_unsuccessfull_coercion(found, expected);
                 }
-                (_, false, _) => {
+                (_, _) => {
                     debug!(
                         "note_type_err: exp_found={:?}, expected={:?} found={:?}",
                         exp_found, expected, found
                     );
-                    if let Some(exp_found) = exp_found {
-                        self.suggest_as_ref_where_appropriate(span, &exp_found, diag);
+                    if !is_simple_error || terr.must_include_note() {
+                        diag.note_expected_found(&expected_label, expected, &found_label, found);
                     }
-
-                    diag.note_expected_found(&"type", expected, found);
                 }
-                _ => (),
             }
         }
+        if let Some(exp_found) = exp_found {
+            self.suggest_as_ref_where_appropriate(span, &exp_found, diag);
+        }
 
         // In some (most?) cases cause.body_id points to actual body, but in some cases
         // it's a actual definition. According to the comments (e.g. in

src/librustc/ty/diagnostics.rs

@@ -0,0 +1,56 @@
+//! Diagnostics related methods for `TyS`.
+
+use crate::ty::TyS;
+use crate::ty::TyKind::*;
+use crate::ty::sty::InferTy;
+
+impl<'tcx> TyS<'tcx> {
+    /// Similar to `TyS::is_primitive`, but also considers inferred numeric values to be primitive.
+    pub fn is_primitive_ty(&self) -> bool {
+        match self.kind {
+            Bool | Char | Str | Int(_) | Uint(_) | Float(_) |
+            Infer(InferTy::IntVar(_)) | Infer(InferTy::FloatVar(_)) |
+            Infer(InferTy::FreshIntTy(_)) | Infer(InferTy::FreshFloatTy(_)) => true,
+            _ => false,
+        }
+    }
+
+    /// Whether the type is succinctly representable as a type instead of just refered to with a
+    /// description in error messages. This is used in the main error message.
+    pub fn is_simple_ty(&self) -> bool {
+        match self.kind {
+            Bool | Char | Str | Int(_) | Uint(_) | Float(_) |
+            Infer(InferTy::IntVar(_)) | Infer(InferTy::FloatVar(_)) |
+            Infer(InferTy::FreshIntTy(_)) | Infer(InferTy::FreshFloatTy(_)) => true,
+            Ref(_, x, _) | Array(x, _) | Slice(x) => x.peel_refs().is_simple_ty(),
+            Tuple(tys) if tys.is_empty() => true,
+            _ => false,
+        }
+    }
+
+    /// Whether the type is succinctly representable as a type instead of just refered to with a
+    /// description in error messages. This is used in the primary span label. Beyond what
+    /// `is_simple_ty` includes, it also accepts ADTs with no type arguments and references to
+    /// ADTs with no type arguments.
+    pub fn is_simple_text(&self) -> bool {
+        match self.kind {
+            Adt(_, substs) => substs.types().next().is_none(),
+            Ref(_, ty, _) => ty.is_simple_text(),
+            _ => self.is_simple_ty(),
+        }
+    }
+
+    /// Whether the type can be safely suggested during error recovery.
+    pub fn is_suggestable(&self) -> bool {
+        match self.kind {
+            Opaque(..) |
+            FnDef(..) |
+            FnPtr(..) |
+            Dynamic(..) |
+            Closure(..) |
+            Infer(..) |
+            Projection(..) => false,
+            _ => true,
+        }
+    }
+}

src/librustc/ty/error.rs

@@ -64,8 +64,11 @@ pub enum UnconstrainedNumeric {
 impl<'tcx> fmt::Display for TypeError<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         use self::TypeError::*;
-        fn report_maybe_different(f: &mut fmt::Formatter<'_>,
-                                  expected: &str, found: &str) -> fmt::Result {
+        fn report_maybe_different(
+            f: &mut fmt::Formatter<'_>,
+            expected: &str,
+            found: &str,
+        ) -> fmt::Result {
             // A naive approach to making sure that we're not reporting silly errors such as:
             // (expected closure, found closure).
             if expected == found {
@@ -183,46 +186,77 @@ impl<'tcx> fmt::Display for TypeError<'tcx> {
     }
 }
 
+impl<'tcx> TypeError<'tcx> {
+    pub fn must_include_note(&self) -> bool {
+        use self::TypeError::*;
+        match self {
+            CyclicTy(_) |
+            UnsafetyMismatch(_) |
+            Mismatch |
+            AbiMismatch(_) |
+            FixedArraySize(_) |
+            Sorts(_) |
+            IntMismatch(_) |
+            FloatMismatch(_) |
+            VariadicMismatch(_) => false,
+
+            Mutability |
+            TupleSize(_) |
+            ArgCount |
+            RegionsDoesNotOutlive(..) |
+            RegionsInsufficientlyPolymorphic(..) |
+            RegionsOverlyPolymorphic(..) |
+            RegionsPlaceholderMismatch |
+            Traits(_) |
+            ProjectionMismatched(_) |
+            ProjectionBoundsLength(_) |
+            ExistentialMismatch(_) |
+            ConstMismatch(_) |
+            IntrinsicCast |
+            ObjectUnsafeCoercion(_) => true,
+        }
+    }
+}
+
 impl<'tcx> ty::TyS<'tcx> {
     pub fn sort_string(&self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
         match self.kind {
             ty::Bool | ty::Char | ty::Int(_) |
-            ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => self.to_string().into(),
-            ty::Tuple(ref tys) if tys.is_empty() => self.to_string().into(),
+            ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => format!("`{}`", self).into(),
+            ty::Tuple(ref tys) if tys.is_empty() => format!("`{}`", self).into(),
 
             ty::Adt(def, _) => format!("{} `{}`", def.descr(), tcx.def_path_str(def.did)).into(),
             ty::Foreign(def_id) => format!("extern type `{}`", tcx.def_path_str(def_id)).into(),
-            ty::Array(_, n) => {
+            ty::Array(t, n) => {
                 let n = tcx.lift(&n).unwrap();
                 match n.try_eval_usize(tcx, ty::ParamEnv::empty()) {
-                    Some(n) => {
-                        format!("array of {} element{}", n, pluralize!(n)).into()
-                    }
+                    _ if t.is_simple_ty() => format!("array `{}`", self).into(),
+                    Some(n) => format!("array of {} element{} ", n, pluralize!(n)).into(),
                     None => "array".into(),
                 }
             }
+            ty::Slice(ty) if ty.is_simple_ty() => format!("slice `{}`", self).into(),
             ty::Slice(_) => "slice".into(),
             ty::RawPtr(_) => "*-ptr".into(),
-            ty::Ref(region, ty, mutbl) => {
+            ty::Ref(_, ty, mutbl) => {
                 let tymut = ty::TypeAndMut { ty, mutbl };
                 let tymut_string = tymut.to_string();
-                if tymut_string == "_" ||         //unknown type name,
-                   tymut_string.len() > 10 ||     //name longer than saying "reference",
-                   region.to_string() != "'_"     //... or a complex type
-                {
-                    format!("{}reference", match mutbl {
-                        hir::Mutability::Mutable => "mutable ",
-                        _ => ""
-                    }).into()
-                } else {
-                    format!("&{}", tymut_string).into()
+                if tymut_string != "_" && (
+                    ty.is_simple_text() || tymut_string.len() < "mutable reference".len()
+                ) {
+                    format!("`&{}`", tymut_string).into()
+                } else { // Unknown type name, it's long or has type arguments
+                    match mutbl {
+                        hir::Mutability::Mutable => "mutable reference",
+                        _ => "reference",
+                    }.into()
                 }
             }
             ty::FnDef(..) => "fn item".into(),
             ty::FnPtr(_) => "fn pointer".into(),
             ty::Dynamic(ref inner, ..) => {
                 if let Some(principal) = inner.principal() {
-                    format!("trait {}", tcx.def_path_str(principal.def_id())).into()
+                    format!("trait `{}`", tcx.def_path_str(principal.def_id())).into()
                 } else {
                     "trait".into()
                 }
@@ -246,6 +280,36 @@ impl<'tcx> ty::TyS<'tcx> {
             ty::Error => "type error".into(),
         }
     }
+
+    pub fn prefix_string(&self) -> Cow<'static, str> {
+        match self.kind {
+            ty::Infer(_) | ty::Error | ty::Bool | ty::Char | ty::Int(_) |
+            ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => "type".into(),
+            ty::Tuple(ref tys) if tys.is_empty() => "unit type".into(),
+            ty::Adt(def, _) => def.descr().into(),
+            ty::Foreign(_) => "extern type".into(),
+            ty::Array(..) => "array".into(),
+            ty::Slice(_) => "slice".into(),
+            ty::RawPtr(_) => "raw pointer".into(),
+            ty::Ref(.., mutbl) => match mutbl {
+                hir::Mutability::Mutable => "mutable reference",
+                _ => "reference"
+            }.into(),
+            ty::FnDef(..) => "fn item".into(),
+            ty::FnPtr(_) => "fn pointer".into(),
+            ty::Dynamic(..) => "trait object".into(),
+            ty::Closure(..) => "closure".into(),
+            ty::Generator(..) => "generator".into(),
+            ty::GeneratorWitness(..) => "generator witness".into(),
+            ty::Tuple(..) => "tuple".into(),
+            ty::Placeholder(..) => "higher-ranked type".into(),
+            ty::Bound(..) => "bound type variable".into(),
+            ty::Projection(_) => "associated type".into(),
+            ty::UnnormalizedProjection(_) => "associated type".into(),
+            ty::Param(_) => "type parameter".into(),
+            ty::Opaque(..) => "opaque type".into(),
+        }
+    }
 }
 
 impl<'tcx> TyCtxt<'tcx> {

src/librustc/ty/mod.rs

@@ -71,6 +71,7 @@ pub use self::sty::BoundRegion::*;
 pub use self::sty::InferTy::*;
 pub use self::sty::RegionKind::*;
 pub use self::sty::TyKind::*;
+pub use crate::ty::diagnostics::*;
 
 pub use self::binding::BindingMode;
 pub use self::binding::BindingMode::*;
@@ -122,6 +123,7 @@ mod instance;
 mod structural_impls;
 mod structural_match;
 mod sty;
+mod diagnostics;
 
 // Data types
 
@@ -552,37 +554,6 @@ impl<'tcx> Hash for TyS<'tcx> {
     }
 }
 
-impl<'tcx> TyS<'tcx> {
-    pub fn is_primitive_ty(&self) -> bool {
-        match self.kind {
-            Bool |
-            Char |
-            Int(_) |
-            Uint(_) |
-            Float(_) |
-            Infer(InferTy::IntVar(_)) |
-            Infer(InferTy::FloatVar(_)) |
-            Infer(InferTy::FreshIntTy(_)) |
-            Infer(InferTy::FreshFloatTy(_)) => true,
-            Ref(_, x, _) => x.is_primitive_ty(),
-            _ => false,
-        }
-    }
-
-    pub fn is_suggestable(&self) -> bool {
-        match self.kind {
-            Opaque(..) |
-            FnDef(..) |
-            FnPtr(..) |
-            Dynamic(..) |
-            Closure(..) |
-            Infer(..) |
-            Projection(..) => false,
-            _ => true,
-        }
-    }
-}
-
 impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for ty::TyS<'tcx> {
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
         let ty::TyS {

src/librustc/ty/wf.rs

@@ -209,7 +209,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
                     //   LL | impl Bar for Foo {
                     //      | ---------------- in this `impl` item
                     //   LL |     type Ok = ();
-                    //      |     ^^^^^^^^^^^^^ expected u32, found ()
+                    //      |     ^^^^^^^^^^^^^ expected `u32`, found `()`
                     //      |
                     //      = note: expected type `u32`
                     //                 found type `()`
@@ -228,7 +228,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
                     //   LL | impl Bar for Foo {
                     //      | ---------------- in this `impl` item
                     //   LL |     type Ok = ();
-                    //      |     ^^^^^^^^^^^^^ expected u32, found ()
+                    //      |     ^^^^^^^^^^^^^ expected `u32`, found `()`
                     //   ...
                     //   LL | impl Bar2 for Foo2 {
                     //      | ---------------- in this `impl` item