Improve self-referential diagnostic somewhat

Author: oli-obk

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -644,20 +644,18 @@ pub trait PrettyPrinter<'tcx>:
                     return Ok(self);
                 }
 
-                return with_no_queries(|| {
-                    let def_key = self.tcx().def_key(def_id);
-                    if let Some(name) = def_key.disambiguated_data.data.get_opt_name() {
-                        p!(write("{}", name));
-                        // FIXME(eddyb) print this with `print_def_path`.
-                        if !substs.is_empty() {
-                            p!("::");
-                            p!(generic_delimiters(|cx| cx.comma_sep(substs.iter())));
-                        }
-                        return Ok(self);
+                let def_key = self.tcx().def_key(def_id);
+                if let Some(name) = def_key.disambiguated_data.data.get_opt_name() {
+                    p!(write("{}", name));
+                    // FIXME(eddyb) print this with `print_def_path`.
+                    if !substs.is_empty() {
+                        p!("::");
+                        p!(generic_delimiters(|cx| cx.comma_sep(substs.iter())));
                     }
+                    return Ok(self);
+                }
 
-                    self.pretty_print_opaque_impl_type(def_id, substs)
-                });
+                return self.pretty_print_opaque_impl_type(def_id, substs);
             }
             ty::Str => p!("str"),
             ty::Generator(did, substs, movability) => {
@@ -900,6 +898,15 @@ pub trait PrettyPrinter<'tcx>:
                     if !first {
                         p!(", ");
                     }
+                    if let GenericArgKind::Type(ty) = ty.unpack() {
+                        if let ty::Opaque(d, substs) = *ty.kind() {
+                            if d == def_id {
+                                p!(print_def_path(d, substs));
+                                first = false;
+                                continue;
+                            }
+                        }
+                    }
                     p!(print(trait_ref.rebind(*ty)));
                     first = false;
                 }

src/test/ui/type-alias-impl-trait/nested.rs

@@ -13,5 +13,5 @@ fn bar() -> Bar {
 
 fn main() {
     println!("{:?}", bar());
-    //~^ ERROR `impl Trait<Opaque(DefId(0:4 ~ nested[14f6]::Foo::{opaque#0}), [])>` doesn't implement `Debug`
+    //~^ ERROR `impl Trait<impl Debug>` doesn't implement `Debug`
 }

src/test/ui/type-alias-impl-trait/nested.stderr

@@ -1,10 +1,10 @@
-error[E0277]: `impl Trait<Opaque(DefId(0:4 ~ nested[14f6]::Foo::{opaque#0}), [])>` doesn't implement `Debug`
+error[E0277]: `impl Trait<impl Debug>` doesn't implement `Debug`
   --> $DIR/nested.rs:15:22
    |
 LL |     println!("{:?}", bar());
-   |                      ^^^^^ `impl Trait<Opaque(DefId(0:4 ~ nested[14f6]::Foo::{opaque#0}), [])>` cannot be formatted using `{:?}` because it doesn't implement `Debug`
+   |                      ^^^^^ `impl Trait<impl Debug>` cannot be formatted using `{:?}` because it doesn't implement `Debug`
    |
-   = help: the trait `Debug` is not implemented for `impl Trait<Opaque(DefId(0:4 ~ nested[14f6]::Foo::{opaque#0}), [])>`
+   = help: the trait `Debug` is not implemented for `impl Trait<impl Debug>`
    = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error

src/test/ui/type-alias-impl-trait/self-referential.rs

@@ -3,7 +3,7 @@
 type Bar<'a, 'b> = impl PartialEq<Bar<'b, 'a>> + std::fmt::Debug;
 
 fn bar<'a, 'b>(i: &'a i32) -> Bar<'a, 'b> {
-    i //~ ERROR can't compare `&i32` with `impl PartialEq<Opaque
+    i //~ ERROR can't compare `&i32` with `impl PartialEq<Bar<'a, 'b>
 }
 
 fn main() {

src/test/ui/type-alias-impl-trait/self-referential.stderr

@@ -1,10 +1,10 @@
-error[E0277]: can't compare `&i32` with `impl PartialEq<Opaque(DefId(0:6 ~ self_referential[5b7d]::Bar::{opaque#0}), [ReFree(DefId(0:7 ~ self_referential[5b7d]::bar), BrNamed(DefId(0:8 ~ self_referential[5b7d]::bar::'a), 'a)), ReEarlyBound(0, 'b)])> + Debug`
+error[E0277]: can't compare `&i32` with `impl PartialEq<Bar<'a, 'b>::{opaque#0}> + Debug`
   --> $DIR/self-referential.rs:6:5
    |
 LL |     i
-   |     ^ no implementation for `&i32 == impl PartialEq<Opaque(DefId(0:6 ~ self_referential[5b7d]::Bar::{opaque#0}), [ReFree(DefId(0:7 ~ self_referential[5b7d]::bar), BrNamed(DefId(0:8 ~ self_referential[5b7d]::bar::'a), 'a)), ReEarlyBound(0, 'b)])> + Debug`
+   |     ^ no implementation for `&i32 == impl PartialEq<Bar<'a, 'b>::{opaque#0}> + Debug`
    |
-   = help: the trait `PartialEq<impl PartialEq<Opaque(DefId(0:6 ~ self_referential[5b7d]::Bar::{opaque#0}), [ReFree(DefId(0:7 ~ self_referential[5b7d]::bar), BrNamed(DefId(0:8 ~ self_referential[5b7d]::bar::'a), 'a)), ReEarlyBound(0, 'b)])> + Debug>` is not implemented for `&i32`
+   = help: the trait `PartialEq<impl PartialEq<Bar<'a, 'b>::{opaque#0}> + Debug>` is not implemented for `&i32`
 
 error: aborting due to previous error