add tests for ICE: 'broken MIR: bad assignment: NoSolution' on trait with default method and no impls

Fixes rust-lang#109869

Author: matthiaskrgr

tests/ui/traits/ice-trait-with-default-method-but-no-impl-broken-mir-109869-1.rs

@@ -0,0 +1,21 @@
+// ICE 'broken MIR: bad assignment: NoSolution'
+// on trait with default method and no impls
+// issue: rust-lang/rust#109869
+
+type Spanned<T> = (T, ());
+
+trait Span<T> {}
+
+impl<T> Span<T> for (T, ()) {}
+
+impl<F, T: From<F>> From<Spanned<F>> for dyn Span<T>
+where
+    Self: Sized
+{
+    fn from((from, ()): Spanned<F>) -> Self {
+        (T::from(from), ())
+        //~^ ERROR mismatched types
+    }
+}
+
+pub fn main() {}

tests/ui/traits/ice-trait-with-default-method-but-no-impl-broken-mir-109869-1.stderr

@@ -0,0 +1,19 @@
+error[E0308]: mismatched types
+  --> $DIR/ice-trait-with-default-method-but-no-impl-broken-mir-109869-1.rs:16:9
+   |
+LL |     fn from((from, ()): Spanned<F>) -> Self {
+   |                                        ---- expected `(dyn Span<T> + 'static)` because of return type
+LL |         (T::from(from), ())
+   |         ^^^^^^^^^^^^^^^^^^^ expected `dyn Span`, found `(T, ())`
+   |
+   = note: expected trait object `(dyn Span<T> + 'static)`
+                     found tuple `(T, ())`
+   = help: `(T, ())` implements `Span` so you could box the found value and coerce it to the trait object `Box<dyn Span>`, you will have to change the expected type as well
+help: call `Into::into` on this expression to convert `(T, ())` into `(dyn Span<T> + 'static)`
+   |
+LL |         (T::from(from), ()).into()
+   |                            +++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/traits/ice-trait-with-default-method-but-no-impl-broken-mir-109869-2.rs

@@ -0,0 +1,17 @@
+// ICE 'broken MIR: bad assignment: NoSolution'
+// on trait with default method and no impls
+// issue: rust-lang/rust#109869
+
+trait Empty<T> {}
+
+impl<T> Default for dyn Empty<T>
+where
+    Self: Sized,
+{
+    fn default() -> Self {
+        ()
+        //~^ ERROR mismatched types
+    }
+}
+
+pub fn main() {}

tests/ui/traits/ice-trait-with-default-method-but-no-impl-broken-mir-109869-2.stderr

@@ -0,0 +1,14 @@
+error[E0308]: mismatched types
+  --> $DIR/ice-trait-with-default-method-but-no-impl-broken-mir-109869-2.rs:12:9
+   |
+LL |     fn default() -> Self {
+   |                     ---- expected `(dyn Empty<T> + 'static)` because of return type
+LL |         ()
+   |         ^^ expected `dyn Empty`, found `()`
+   |
+   = note: expected trait object `(dyn Empty<T> + 'static)`
+                 found unit type `()`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/traits/ice-trait-with-default-method-but-no-impl-broken-mir-109869-trivial-bounds.rs

@@ -0,0 +1,18 @@
+// ICE 'broken MIR: bad assignment: NoSolution'
+// on trait with default method and no impls
+// issue: rust-lang/rust#109869
+
+#![feature(trivial_bounds)]
+trait Empty {}
+
+impl Default for dyn Empty
+where
+    Self: Sized,
+{
+    fn default() -> Self {
+        ()
+        //~^ ERROR mismatched types
+    }
+}
+
+pub fn main() {}

tests/ui/traits/ice-trait-with-default-method-but-no-impl-broken-mir-109869-trivial-bounds.stderr

@@ -0,0 +1,14 @@
+error[E0308]: mismatched types
+  --> $DIR/ice-trait-with-default-method-but-no-impl-broken-mir-109869-trivial-bounds.rs:13:9
+   |
+LL |     fn default() -> Self {
+   |                     ---- expected `(dyn Empty + 'static)` because of return type
+LL |         ()
+   |         ^^ expected `dyn Empty`, found `()`
+   |
+   = note: expected trait object `(dyn Empty + 'static)`
+                 found unit type `()`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.