Print opaque types from type aliases via their path

Author: oli-obk

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

@@ -644,18 +644,23 @@ pub trait PrettyPrinter<'tcx>:
                     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())));
+                let parent = self.tcx().parent(def_id).expect("opaque types always have a parent");
+                match self.tcx().def_kind(parent) {
+                    DefKind::TyAlias | DefKind::AssocTy => {
+                        if let ty::Opaque(d, _) = *self.tcx().type_of(parent).kind() {
+                            if d == def_id {
+                                // If the type alias directly starts with the `impl` of the
+                                // opaque type we're printing, then skip the `::{opaque#1}`.
+                                p!(print_def_path(parent, substs));
+                                return Ok(self);
+                            }
+                        }
+                        // Complex opaque type, e.g. `type Foo = (i32, impl Debug);`
+                        p!(print_def_path(def_id, substs));
+                        return Ok(self);
                     }
-                    return Ok(self);
+                    _ => return 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) => {
@@ -898,15 +903,6 @@ 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/associated-type-bounds/assoc-type-eq-with-dyn-atb-fail.stderr

@@ -4,7 +4,7 @@ error[E0277]: the trait bound `String: Copy` is not satisfied
 LL |         Box::new(AssocNoCopy)
    |         ^^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `String`
    |
-   = note: required for the cast to the object type `dyn Bar<Assoc = impl Copy>`
+   = note: required for the cast to the object type `dyn Bar<Assoc = <AssocNoCopy as Thing>::Out::{opaque#0}>`
 
 error: aborting due to previous error
 

src/test/ui/impl-trait/auto-trait.rs

@@ -19,7 +19,7 @@ impl<T: Send> AnotherTrait for T {}
 // (We treat opaque types as "foreign types" that could grow more impls
 // in the future.)
 impl AnotherTrait for D<OpaqueType> {
-    //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<impl OpaqueTrait>`
+    //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
 }
 
 fn main() {}

src/test/ui/impl-trait/auto-trait.stderr

@@ -1,11 +1,11 @@
-error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<impl OpaqueTrait>`
+error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
   --> $DIR/auto-trait.rs:21:1
    |
 LL | impl<T: Send> AnotherTrait for T {}
    | -------------------------------- first implementation here
 ...
 LL | impl AnotherTrait for D<OpaqueType> {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<impl OpaqueTrait>`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<OpaqueType>`
 
 error: aborting due to previous error
 

src/test/ui/impl-trait/negative-reasoning.rs

@@ -17,7 +17,7 @@ impl<T: std::fmt::Debug> AnotherTrait for T {}
 
 // This is in error, because we cannot assume that `OpaqueType: !Debug`
 impl AnotherTrait for D<OpaqueType> {
-    //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<impl OpaqueTrait>`
+    //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
 }
 
 fn main() {}

src/test/ui/impl-trait/negative-reasoning.stderr

@@ -1,13 +1,13 @@
-error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<impl OpaqueTrait>`
+error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
   --> $DIR/negative-reasoning.rs:19:1
    |
 LL | impl<T: std::fmt::Debug> AnotherTrait for T {}
    | ------------------------------------------- first implementation here
 ...
 LL | impl AnotherTrait for D<OpaqueType> {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<impl OpaqueTrait>`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<OpaqueType>`
    |
-   = note: upstream crates may add a new impl of trait `std::fmt::Debug` for type `impl OpaqueTrait` in future versions
+   = note: upstream crates may add a new impl of trait `std::fmt::Debug` for type `OpaqueType` in future versions
 
 error: aborting due to previous error
 

src/test/ui/lint/lint-ctypes-73249-2.rs

@@ -23,7 +23,7 @@ pub struct A<T: Foo> {
 }
 
 extern "C" {
-    pub fn lint_me() -> A<()>; //~ ERROR: uses type `impl Baz`
+    pub fn lint_me() -> A<()>; //~ ERROR: uses type `Qux`
 }
 
 fn main() {}

src/test/ui/lint/lint-ctypes-73249-2.stderr

@@ -1,4 +1,4 @@
-error: `extern` block uses type `impl Baz`, which is not FFI-safe
+error: `extern` block uses type `Qux`, which is not FFI-safe
   --> $DIR/lint-ctypes-73249-2.rs:26:25
    |
 LL |     pub fn lint_me() -> A<()>;

src/test/ui/lint/lint-ctypes-73249-3.rs

@@ -17,7 +17,7 @@ pub struct A {
 }
 
 extern "C" {
-    pub fn lint_me() -> A; //~ ERROR: uses type `impl Baz`
+    pub fn lint_me() -> A; //~ ERROR: uses type `Qux`
 }
 
 fn main() {}

src/test/ui/lint/lint-ctypes-73249-3.stderr

@@ -1,4 +1,4 @@
-error: `extern` block uses type `impl Baz`, which is not FFI-safe
+error: `extern` block uses type `Qux`, which is not FFI-safe
   --> $DIR/lint-ctypes-73249-3.rs:20:25
    |
 LL |     pub fn lint_me() -> A;