Rollup merge of #119818 - oli-obk:even_more_follow_up_errors3, r=comp…

…iler-errors

Silence some follow-up errors [3/x]

this is one piece of the requested cleanups from #117449

Keep error types around, even in obligations.

These help silence follow-up errors, as we now figure out that some types (most notably inference variables) are equal to an error type.

But it also allows figuring out more types in the presence of errors, possibly causing more errors.

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -631,13 +631,6 @@ impl<'tcx> InferCtxt<'tcx> {
                 ct_op: |ct| ct,
             });
 
-            if let ty::ClauseKind::Projection(projection) = predicate.kind().skip_binder() {
-                if projection.term.references_error() {
-                    // No point on adding any obligations since there's a type error involved.
-                    obligations.clear();
-                    return;
-                }
-            }
             // Require that the predicate holds for the concrete type.
             debug!(?predicate);
             obligations.push(traits::Obligation::new(

tests/ui/async-await/issues/issue-65159.rs

@@ -5,7 +5,7 @@
 async fn copy() -> Result<()>
 //~^ ERROR enum takes 2 generic arguments
 {
-    Ok(()) //~ ERROR: type annotations needed
+    Ok(())
 }
 
-fn main() { }
+fn main() {}

tests/ui/async-await/issues/issue-65159.stderr

@@ -11,18 +11,6 @@ help: add missing generic argument
 LL | async fn copy() -> Result<(), E>
    |                             +++
 
-error[E0282]: type annotations needed
-  --> $DIR/issue-65159.rs:8:5
-   |
-LL |     Ok(())
-   |     ^^ cannot infer type of the type parameter `E` declared on the enum `Result`
-   |
-help: consider specifying the generic arguments
-   |
-LL |     Ok::<(), E>(())
-   |       +++++++++
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0107, E0282.
-For more information about an error, try `rustc --explain E0107`.
+For more information about this error, try `rustc --explain E0107`.

tests/ui/borrowck/issue-82126-mismatched-subst-and-hir.rs

@@ -17,7 +17,6 @@ async fn buy_lock(coroutine: &Mutex<MarketMultiplier>) -> LockedMarket<'_> {
     //~^ ERROR struct takes 0 lifetime arguments but 1 lifetime argument was supplied
     //~^^ ERROR struct takes 1 generic argument but 0 generic arguments were supplied
     LockedMarket(coroutine.lock().unwrap().buy())
-    //~^ ERROR: cannot return value referencing temporary value
 }
 
 struct LockedMarket<T>(T);

tests/ui/borrowck/issue-82126-mismatched-subst-and-hir.stderr

@@ -7,7 +7,7 @@ LL | async fn buy_lock(coroutine: &Mutex<MarketMultiplier>) -> LockedMarket<'_>
    |                                                           expected 0 lifetime arguments
    |
 note: struct defined here, with 0 lifetime parameters
-  --> $DIR/issue-82126-mismatched-subst-and-hir.rs:23:8
+  --> $DIR/issue-82126-mismatched-subst-and-hir.rs:22:8
    |
 LL | struct LockedMarket<T>(T);
    |        ^^^^^^^^^^^^
@@ -19,7 +19,7 @@ LL | async fn buy_lock(coroutine: &Mutex<MarketMultiplier>) -> LockedMarket<'_>
    |                                                           ^^^^^^^^^^^^ expected 1 generic argument
    |
 note: struct defined here, with 1 generic parameter: `T`
-  --> $DIR/issue-82126-mismatched-subst-and-hir.rs:23:8
+  --> $DIR/issue-82126-mismatched-subst-and-hir.rs:22:8
    |
 LL | struct LockedMarket<T>(T);
    |        ^^^^^^^^^^^^ -
@@ -28,16 +28,6 @@ help: add missing generic argument
 LL | async fn buy_lock(coroutine: &Mutex<MarketMultiplier>) -> LockedMarket<'_, T> {
    |                                                                          +++
 
-error[E0515]: cannot return value referencing temporary value
-  --> $DIR/issue-82126-mismatched-subst-and-hir.rs:19:5
-   |
-LL |     LockedMarket(coroutine.lock().unwrap().buy())
-   |     ^^^^^^^^^^^^^-------------------------^^^^^^^
-   |     |            |
-   |     |            temporary value created here
-   |     returns a value referencing data owned by the current function
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0107, E0515.
-For more information about an error, try `rustc --explain E0107`.
+For more information about this error, try `rustc --explain E0107`.

tests/ui/impl-trait/issue-72911.rs

@@ -15,6 +15,7 @@ fn gather_from_file(dir_entry: &foo::MissingItem) -> impl Iterator<Item = Lint>
 
 fn lint_files() -> impl Iterator<Item = foo::MissingItem> {
     //~^ ERROR: failed to resolve
+    //~| ERROR: `()` is not an iterator
     unimplemented!()
 }
 

tests/ui/impl-trait/issue-72911.stderr

@@ -1,3 +1,11 @@
+error[E0277]: `()` is not an iterator
+  --> $DIR/issue-72911.rs:16:20
+   |
+LL | fn lint_files() -> impl Iterator<Item = foo::MissingItem> {
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `()` is not an iterator
+   |
+   = help: the trait `Iterator` is not implemented for `()`
+
 error[E0433]: failed to resolve: use of undeclared crate or module `foo`
   --> $DIR/issue-72911.rs:11:33
    |
@@ -10,6 +18,7 @@ error[E0433]: failed to resolve: use of undeclared crate or module `foo`
 LL | fn lint_files() -> impl Iterator<Item = foo::MissingItem> {
    |                                         ^^^ use of undeclared crate or module `foo`
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0433`.
+Some errors have detailed explanations: E0277, E0433.
+For more information about an error, try `rustc --explain E0277`.

tests/ui/impl-trait/issues/issue-92305.rs

@@ -5,7 +5,6 @@ use std::iter;
 fn f<T>(data: &[T]) -> impl Iterator<Item = Vec> {
     //~^ ERROR: missing generics for struct `Vec` [E0107]
     iter::empty()
-    //~^ ERROR: type annotations needed
 }
 
 fn g<T>(data: &[T], target: T) -> impl Iterator<Item = Vec<T>> {

tests/ui/impl-trait/issues/issue-92305.stderr

@@ -9,18 +9,6 @@ help: add missing generic argument
 LL | fn f<T>(data: &[T]) -> impl Iterator<Item = Vec<T>> {
    |                                                +++
 
-error[E0282]: type annotations needed
-  --> $DIR/issue-92305.rs:7:5
-   |
-LL |     iter::empty()
-   |     ^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the function `empty`
-   |
-help: consider specifying the generic argument
-   |
-LL |     iter::empty::<T>()
-   |                +++++
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0107, E0282.
-For more information about an error, try `rustc --explain E0107`.
+For more information about this error, try `rustc --explain E0107`.