Rollup merge of #64746 - estebank:elide-impl-trait-obligations-on-err, r=cramertj

Remove blanket silencing of "type annotation needed" errors

Remove blanket check for existence of other errors before emitting "type annotation needed" errors, and add some eager checks to avoid adding obligations when they refer to types that reference `[type error]` in order to reduce unneeded errors.

Fix #64084.

2 files changed, 60 insertions, 46 deletions

diff --git a/src/test/ui/impl-trait/where-allowed.rs b/src/test/ui/impl-trait/where-allowed.rs
index 9eac6b714de..65c4b78bf6a 100644
--- a/src/test/ui/impl-trait/where-allowed.rs
+++ b/src/test/ui/impl-trait/where-allowed.rs
@@ -11,8 +11,9 @@ fn in_return() -> impl Debug { panic!() }
 // Allowed
 fn in_adt_in_parameters(_: Vec<impl Debug>) { panic!() }
 
-// Allowed
+// Disallowed
 fn in_adt_in_return() -> Vec<impl Debug> { panic!() }
+//~^ ERROR type annotations needed
 
 // Disallowed
 fn in_fn_parameter_in_parameters(_: fn(impl Debug)) { panic!() }
@@ -58,7 +59,8 @@ fn in_impl_Fn_return_in_parameters(_: &impl Fn() -> impl Debug) { panic!() }
 // Disallowed
 fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() }
 //~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
-//~^^ ERROR nested `impl Trait` is not allowed
+//~| ERROR nested `impl Trait` is not allowed
+//~| ERROR type annotations needed
 
 // Disallowed
 fn in_impl_Fn_return_in_return() -> &'static impl Fn() -> impl Debug { panic!() }
diff --git a/src/test/ui/impl-trait/where-allowed.stderr b/src/test/ui/impl-trait/where-allowed.stderr
index 1332fff84f5..dfb6e6524d9 100644
--- a/src/test/ui/impl-trait/where-allowed.stderr
+++ b/src/test/ui/impl-trait/where-allowed.stderr
@@ -1,5 +1,5 @@
 error[E0666]: nested `impl Trait` is not allowed
-  --> $DIR/where-allowed.rs:50:51
+  --> $DIR/where-allowed.rs:51:51
    |
 LL | fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() }
    |                                           --------^^^^^^^^^^-
@@ -8,7 +8,7 @@ LL | fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() }
    |                                           outer `impl Trait`
 
 error[E0666]: nested `impl Trait` is not allowed
-  --> $DIR/where-allowed.rs:59:57
+  --> $DIR/where-allowed.rs:60:57
    |
 LL | fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() }
    |                                                 --------^^^^^^^^^^-
@@ -17,7 +17,7 @@ LL | fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic
    |                                                 outer `impl Trait`
 
 error[E0658]: `impl Trait` in type aliases is unstable
-  --> $DIR/where-allowed.rs:122:5
+  --> $DIR/where-allowed.rs:124:5
    |
 LL |     type Out = impl Debug;
    |     ^^^^^^^^^^^^^^^^^^^^^^
@@ -26,7 +26,7 @@ LL |     type Out = impl Debug;
    = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
 
 error[E0658]: `impl Trait` in type aliases is unstable
-  --> $DIR/where-allowed.rs:158:1
+  --> $DIR/where-allowed.rs:160:1
    |
 LL | type InTypeAlias<R> = impl Debug;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -35,205 +35,205 @@ LL | type InTypeAlias<R> = impl Debug;
    = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:18:40
+  --> $DIR/where-allowed.rs:19:40
    |
 LL | fn in_fn_parameter_in_parameters(_: fn(impl Debug)) { panic!() }
    |                                        ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:22:42
+  --> $DIR/where-allowed.rs:23:42
    |
 LL | fn in_fn_return_in_parameters(_: fn() -> impl Debug) { panic!() }
    |                                          ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:26:38
+  --> $DIR/where-allowed.rs:27:38
    |
 LL | fn in_fn_parameter_in_return() -> fn(impl Debug) { panic!() }
    |                                      ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:30:40
+  --> $DIR/where-allowed.rs:31:40
    |
 LL | fn in_fn_return_in_return() -> fn() -> impl Debug { panic!() }
    |                                        ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:34:49
+  --> $DIR/where-allowed.rs:35:49
    |
 LL | fn in_dyn_Fn_parameter_in_parameters(_: &dyn Fn(impl Debug)) { panic!() }
    |                                                 ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:38:51
+  --> $DIR/where-allowed.rs:39:51
    |
 LL | fn in_dyn_Fn_return_in_parameters(_: &dyn Fn() -> impl Debug) { panic!() }
    |                                                   ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:42:55
+  --> $DIR/where-allowed.rs:43:55
    |
 LL | fn in_dyn_Fn_parameter_in_return() -> &'static dyn Fn(impl Debug) { panic!() }
    |                                                       ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:46:57
+  --> $DIR/where-allowed.rs:47:57
    |
 LL | fn in_dyn_Fn_return_in_return() -> &'static dyn Fn() -> impl Debug { panic!() }
    |                                                         ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:50:51
+  --> $DIR/where-allowed.rs:51:51
    |
 LL | fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() }
    |                                                   ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:55:53
+  --> $DIR/where-allowed.rs:56:53
    |
 LL | fn in_impl_Fn_return_in_parameters(_: &impl Fn() -> impl Debug) { panic!() }
    |                                                     ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:59:57
+  --> $DIR/where-allowed.rs:60:57
    |
 LL | fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() }
    |                                                         ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:64:59
+  --> $DIR/where-allowed.rs:66:59
    |
 LL | fn in_impl_Fn_return_in_return() -> &'static impl Fn() -> impl Debug { panic!() }
    |                                                           ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:68:38
+  --> $DIR/where-allowed.rs:70:38
    |
 LL | fn in_Fn_parameter_in_generics<F: Fn(impl Debug)> (_: F) { panic!() }
    |                                      ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:72:40
+  --> $DIR/where-allowed.rs:74:40
    |
 LL | fn in_Fn_return_in_generics<F: Fn() -> impl Debug> (_: F) { panic!() }
    |                                        ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:85:32
+  --> $DIR/where-allowed.rs:87:32
    |
 LL | struct InBraceStructField { x: impl Debug }
    |                                ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:89:41
+  --> $DIR/where-allowed.rs:91:41
    |
 LL | struct InAdtInBraceStructField { x: Vec<impl Debug> }
    |                                         ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:93:27
+  --> $DIR/where-allowed.rs:95:27
    |
 LL | struct InTupleStructField(impl Debug);
    |                           ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:98:25
+  --> $DIR/where-allowed.rs:100:25
    |
 LL |     InBraceVariant { x: impl Debug },
    |                         ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:100:20
+  --> $DIR/where-allowed.rs:102:20
    |
 LL |     InTupleVariant(impl Debug),
    |                    ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:111:23
+  --> $DIR/where-allowed.rs:113:23
    |
 LL |     fn in_return() -> impl Debug;
    |                       ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:129:34
+  --> $DIR/where-allowed.rs:131:34
    |
 LL |     fn in_trait_impl_return() -> impl Debug { () }
    |                                  ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:142:33
+  --> $DIR/where-allowed.rs:144:33
    |
 LL |     fn in_foreign_parameters(_: impl Debug);
    |                                 ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:145:31
+  --> $DIR/where-allowed.rs:147:31
    |
 LL |     fn in_foreign_return() -> impl Debug;
    |                               ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:162:39
+  --> $DIR/where-allowed.rs:164:39
    |
 LL | type InReturnInTypeAlias<R> = fn() -> impl Debug;
    |                                       ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:166:16
+  --> $DIR/where-allowed.rs:168:16
    |
 LL | impl PartialEq<impl Debug> for () {
    |                ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:171:24
+  --> $DIR/where-allowed.rs:173:24
    |
 LL | impl PartialEq<()> for impl Debug {
    |                        ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:176:6
+  --> $DIR/where-allowed.rs:178:6
    |
 LL | impl impl Debug {
    |      ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:182:24
+  --> $DIR/where-allowed.rs:184:24
    |
 LL | impl InInherentImplAdt<impl Debug> {
    |                        ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:188:11
+  --> $DIR/where-allowed.rs:190:11
    |
 LL |     where impl Debug: Debug
    |           ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:195:15
+  --> $DIR/where-allowed.rs:197:15
    |
 LL |     where Vec<impl Debug>: Debug
    |               ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:202:24
+  --> $DIR/where-allowed.rs:204:24
    |
 LL |     where T: PartialEq<impl Debug>
    |                        ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:209:17
+  --> $DIR/where-allowed.rs:211:17
    |
 LL |     where T: Fn(impl Debug)
    |                 ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:216:22
+  --> $DIR/where-allowed.rs:218:22
    |
 LL |     where T: Fn() -> impl Debug
    |                      ^^^^^^^^^^
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:222:29
+  --> $DIR/where-allowed.rs:224:29
    |
 LL |     let _in_local_variable: impl Fn() = || {};
    |                             ^^^^^^^^^
@@ -241,24 +241,36 @@ LL |     let _in_local_variable: impl Fn() = || {};
    = help: add `#![feature(impl_trait_in_bindings)]` to the crate attributes to enable
 
 error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
-  --> $DIR/where-allowed.rs:224:46
+  --> $DIR/where-allowed.rs:226:46
    |
 LL |     let _in_return_in_local_variable = || -> impl Fn() { || {} };
    |                                              ^^^^^^^^^
 
+error[E0282]: type annotations needed
+  --> $DIR/where-allowed.rs:15:30
+   |
+LL | fn in_adt_in_return() -> Vec<impl Debug> { panic!() }
+   |                              ^^^^^^^^^^ cannot infer type
+
+error[E0282]: type annotations needed
+  --> $DIR/where-allowed.rs:60:49
+   |
+LL | fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() }
+   |                                                 ^^^^^^^^^^^^^^^^^^^ cannot infer type
+
 error: could not find defining uses
-  --> $DIR/where-allowed.rs:158:1
+  --> $DIR/where-allowed.rs:160:1
    |
 LL | type InTypeAlias<R> = impl Debug;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: could not find defining uses
-  --> $DIR/where-allowed.rs:122:5
+  --> $DIR/where-allowed.rs:124:5
    |
 LL |     type Out = impl Debug;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 41 previous errors
+error: aborting due to 43 previous errors
 
-Some errors have detailed explanations: E0562, E0658.
-For more information about an error, try `rustc --explain E0562`.
+Some errors have detailed explanations: E0282, E0562, E0658.
+For more information about an error, try `rustc --explain E0282`.