Suppress errors due to TypeError not coercing with inference variables

compiler/rustc_hir_typeck/src/coercion.rs

@@ -171,6 +171,10 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
 
         // Just ignore error types.
         if a.references_error() || b.references_error() {
+            // Best-effort try to unify these types -- we're already on the error path,
+            // so this will have the side-effect of making sure we have no ambiguities
+            // due to `[type error]` and `_` not coercing together.
+            let _ = self.commit_if_ok(|_| self.at(&self.cause, self.param_env).eq(a, b));
             return success(vec![], self.fcx.tcx.ty_error(), vec![]);
         }
 

src/test/ui/expr/malformed_closure/ruby_style_closure.rs

@@ -8,7 +8,6 @@
 
 fn main() {
     let p = Some(45).and_then({
-        //~^ expected a `FnOnce<({integer},)>` closure, found `Option<_>`
         |x| println!("doubling {}", x);
         Some(x * 2)
         //~^ ERROR: cannot find value `x` in this scope

src/test/ui/expr/malformed_closure/ruby_style_closure.stderr

@@ -1,29 +1,9 @@
 error[E0425]: cannot find value `x` in this scope
-  --> $DIR/ruby_style_closure.rs:13:14
+  --> $DIR/ruby_style_closure.rs:12:14
    |
 LL |         Some(x * 2)
    |              ^ not found in this scope
 
-error[E0277]: expected a `FnOnce<({integer},)>` closure, found `Option<_>`
-  --> $DIR/ruby_style_closure.rs:10:31
-   |
-LL |       let p = Some(45).and_then({
-   |  ______________________--------_^
-   | |                      |
-   | |                      required by a bound introduced by this call
-LL | |
-LL | |         |x| println!("doubling {}", x);
-LL | |         Some(x * 2)
-   | |         ----------- this tail expression is of type `Option<_>`
-LL | |
-LL | |     });
-   | |_____^ expected an `FnOnce<({integer},)>` closure, found `Option<_>`
-   |
-   = help: the trait `FnOnce<({integer},)>` is not implemented for `Option<_>`
-note: required by a bound in `Option::<T>::and_then`
-  --> $SRC_DIR/core/src/option.rs:LL:COL
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0277, E0425.
-For more information about an error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0425`.

src/test/ui/functions-closures/fn-help-with-err.rs

@@ -4,7 +4,6 @@ struct Foo;
 
 trait Bar {
     //~^ NOTE `Bar` defines an item `bar`, perhaps you need to implement it
-    //~| NOTE `Bar` defines an item `bar`, perhaps you need to implement it
     fn bar(&self) {}
 }
 
@@ -15,9 +14,6 @@ fn main() {
     //~^ ERROR cannot find value `oops` in this scope
     //~| NOTE not found
     arc.bar();
-    //~^ ERROR no method named `bar`
-    //~| NOTE method not found
-    //~| HELP items from traits can only be used if the trait is implemented and in scope
 
     let arc2 = std::sync::Arc::new(|| Foo);
     arc2.bar();

src/test/ui/functions-closures/fn-help-with-err.stderr

@@ -1,27 +1,14 @@
 error[E0425]: cannot find value `oops` in this scope
-  --> $DIR/fn-help-with-err.rs:14:35
+  --> $DIR/fn-help-with-err.rs:13:35
    |
 LL |     let arc = std::sync::Arc::new(oops);
    |                                   ^^^^ not found in this scope
 
-error[E0599]: no method named `bar` found for struct `Arc<_>` in the current scope
-  --> $DIR/fn-help-with-err.rs:17:9
-   |
-LL |     arc.bar();
-   |         ^^^ method not found in `Arc<_>`
-   |
-   = help: items from traits can only be used if the trait is implemented and in scope
-note: `Bar` defines an item `bar`, perhaps you need to implement it
-  --> $DIR/fn-help-with-err.rs:5:1
-   |
-LL | trait Bar {
-   | ^^^^^^^^^
-
-error[E0599]: no method named `bar` found for struct `Arc<[closure@fn-help-with-err.rs:22:36]>` in the current scope
-  --> $DIR/fn-help-with-err.rs:23:10
+error[E0599]: no method named `bar` found for struct `Arc<[closure@fn-help-with-err.rs:18:36]>` in the current scope
+  --> $DIR/fn-help-with-err.rs:19:10
    |
 LL |     arc2.bar();
-   |          ^^^ method not found in `Arc<[closure@fn-help-with-err.rs:22:36]>`
+   |          ^^^ method not found in `Arc<[closure@fn-help-with-err.rs:18:36]>`
    |
    = help: items from traits can only be used if the trait is implemented and in scope
 note: `Bar` defines an item `bar`, perhaps you need to implement it
@@ -34,7 +21,7 @@ help: use parentheses to call this closure
 LL |     arc2().bar();
    |         ++
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
 Some errors have detailed explanations: E0425, E0599.
 For more information about an error, try `rustc --explain E0425`.

src/test/ui/impl-trait/issue-72911.rs

@@ -5,7 +5,6 @@ pub struct Lint {}
 impl Lint {}
 
 pub fn gather_all() -> impl Iterator<Item = Lint> {
-    //~^ ERROR type annotations needed
     lint_files().flat_map(|f| gather_from_file(&f))
 }
 

src/test/ui/impl-trait/issue-72911.stderr

@@ -1,22 +1,15 @@
 error[E0433]: failed to resolve: use of undeclared crate or module `foo`
-  --> $DIR/issue-72911.rs:12:33
+  --> $DIR/issue-72911.rs:11:33
    |
 LL | fn gather_from_file(dir_entry: &foo::MissingItem) -> impl Iterator<Item = Lint> {
    |                                 ^^^ use of undeclared crate or module `foo`
 
 error[E0433]: failed to resolve: use of undeclared crate or module `foo`
-  --> $DIR/issue-72911.rs:17:41
+  --> $DIR/issue-72911.rs:16:41
    |
 LL | fn lint_files() -> impl Iterator<Item = foo::MissingItem> {
    |                                         ^^^ use of undeclared crate or module `foo`
 
-error[E0282]: type annotations needed
-  --> $DIR/issue-72911.rs:7:24
-   |
-LL | pub fn gather_all() -> impl Iterator<Item = Lint> {
-   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0282, E0433.
-For more information about an error, try `rustc --explain E0282`.
+For more information about this error, try `rustc --explain E0433`.

src/test/ui/methods/issues/issue-90315.rs

@@ -69,8 +69,7 @@ fn main() {
     //~^ ERROR `usize` is not an iterator
 
     let _res: i32 = ..6.take(2).sum();
-    //~^ can't call method `take` on ambiguous numeric type
-    //~| ERROR mismatched types [E0308]
+    //~^ ERROR can't call method `take` on ambiguous numeric type
     //~| HELP you must specify a concrete type for this numeric value
     // Won't suggest because `RangeTo` dest not implemented `take`
 }

src/test/ui/methods/issues/issue-90315.stderr

@@ -184,18 +184,7 @@ help: you must specify a concrete type for this numeric value, like `i32`
 LL |     let _res: i32 = ..6_i32.take(2).sum();
    |                       ~~~~~
 
-error[E0308]: mismatched types
-  --> $DIR/issue-90315.rs:71:21
-   |
-LL |     let _res: i32 = ..6.take(2).sum();
-   |               ---   ^^^^^^^^^^^^^^^^^ expected `i32`, found struct `RangeTo`
-   |               |
-   |               expected due to this
-   |
-   = note: expected type `i32`
-            found struct `RangeTo<_>`
-
-error: aborting due to 19 previous errors
+error: aborting due to 18 previous errors
 
 Some errors have detailed explanations: E0308, E0599, E0689.
 For more information about an error, try `rustc --explain E0308`.

src/test/ui/typeck/nonexistent-field-not-ambiguous.rs

@@ -0,0 +1,8 @@
+struct Foo {
+    val: MissingType,
+    //~^ ERROR cannot find type `MissingType` in this scope
+}
+
+fn main() {
+    Foo { val: Default::default() };
+}

src/test/ui/typeck/nonexistent-field-not-ambiguous.stderr

@@ -0,0 +1,9 @@
+error[E0412]: cannot find type `MissingType` in this scope
+  --> $DIR/nonexistent-field-not-ambiguous.rs:2:10
+   |
+LL |     val: MissingType,
+   |          ^^^^^^^^^^^ not found in this scope
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0412`.