add tests for structured suggestion

src/test/ui/suggestions/object-unsafe-trait-references-self.rs

@@ -0,0 +1,12 @@
+trait Trait {
+    fn baz(&self, _: Self) {}
+    fn bat(&self) -> Self {}
+}
+
+fn bar(x: &dyn Trait) {} //~ ERROR the trait `Trait` cannot be made into an object
+
+trait Other: Sized {}
+
+fn foo(x: &dyn Other) {} //~ ERROR the trait `Other` cannot be made into an object
+
+fn main() {}

src/test/ui/suggestions/object-unsafe-trait-references-self.stderr

@@ -0,0 +1,30 @@
+error[E0038]: the trait `Trait` cannot be made into an object
+  --> $DIR/object-unsafe-trait-references-self.rs:6:11
+   |
+LL | trait Trait {
+   |       ----- this trait cannot be made into an object...
+LL |     fn baz(&self, _: Self) {}
+   |                      ---- ...because method `baz` references the `Self` type in this parameter
+LL |     fn bat(&self) -> Self {}
+   |                      ---- ...because method `bat` references the `Self` type in its return type
+...
+LL | fn bar(x: &dyn Trait) {}
+   |           ^^^^^^^^^^ the trait `Trait` cannot be made into an object
+   |
+   = help: consider moving `baz` to another trait
+   = help: consider moving `bat` to another trait
+
+error[E0038]: the trait `Other` cannot be made into an object
+  --> $DIR/object-unsafe-trait-references-self.rs:10:11
+   |
+LL | trait Other: Sized {}
+   |       -----  ----- ...because it requires `Self: Sized`
+   |       |
+   |       this trait cannot be made into an object...
+LL | 
+LL | fn foo(x: &dyn Other) {}
+   |           ^^^^^^^^^^ the trait `Other` cannot be made into an object
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0038`.

src/test/ui/suggestions/object-unsafe-trait-should-use-where-sized.fixed

@@ -0,0 +1,13 @@
+// run-rustfix
+#![allow(unused_variables, dead_code)]
+
+trait Trait {
+    fn foo() where Self: Other, Self: Sized, { }
+    fn bar(self: &Self) {} //~ ERROR invalid `self` parameter type
+}
+
+fn bar(x: &dyn Trait) {} //~ ERROR the trait `Trait` cannot be made into an object
+
+trait Other {}
+
+fn main() {}

src/test/ui/suggestions/object-unsafe-trait-should-use-where-sized.rs

@@ -0,0 +1,13 @@
+// run-rustfix
+#![allow(unused_variables, dead_code)]
+
+trait Trait {
+    fn foo() where Self: Other, { }
+    fn bar(self: ()) {} //~ ERROR invalid `self` parameter type
+}
+
+fn bar(x: &dyn Trait) {} //~ ERROR the trait `Trait` cannot be made into an object
+
+trait Other {}
+
+fn main() {}

src/test/ui/suggestions/object-unsafe-trait-should-use-where-sized.stderr

@@ -0,0 +1,35 @@
+error[E0038]: the trait `Trait` cannot be made into an object
+  --> $DIR/object-unsafe-trait-should-use-where-sized.rs:9:11
+   |
+LL | trait Trait {
+   |       ----- this trait cannot be made into an object...
+LL |     fn foo() where Self: Other, { }
+   |        --- ...because associated function `foo` has no `self` parameter
+LL |     fn bar(self: ()) {}
+   |                  -- ...because method `bar`'s `self` parameter cannot be dispatched on
+...
+LL | fn bar(x: &dyn Trait) {}
+   |           ^^^^^^^^^^ the trait `Trait` cannot be made into an object
+   |
+help: consider turning `foo` into a method by giving it a `&self` argument or constraining it so it does not apply to trait objects
+   |
+LL |     fn foo() where Self: Other, Self: Sized, { }
+   |                               ^^^^^^^^^^^^^
+help: consider changing method `bar`'s `self` parameter to be `&self`
+   |
+LL |     fn bar(self: &Self) {}
+   |                  ^^^^^
+
+error[E0307]: invalid `self` parameter type: ()
+  --> $DIR/object-unsafe-trait-should-use-where-sized.rs:6:18
+   |
+LL |     fn bar(self: ()) {}
+   |                  ^^
+   |
+   = note: type of `self` must be `Self` or a type that dereferences to it
+   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0038, E0307.
+For more information about an error, try `rustc --explain E0038`.