suggest similarly named type when use of undeclared type

Author: m-ysk

compiler/rustc_resolve/src/diagnostics.rs

@@ -2059,7 +2059,13 @@ impl<'a> Resolver<'a> {
                     Applicability::MaybeIncorrect,
                 ))
             } else {
-                None
+                self.find_similarly_named_type(ident.name, ribs).map(|sugg| {
+                    (
+                        vec![(ident.span, sugg.to_string())],
+                        String::from("there is a type with a similar name"),
+                        Applicability::MaybeIncorrect,
+                    )
+                })
             };
 
             (format!("use of undeclared type `{}`", ident), suggestion)

src/test/ui/generic-associated-types/equality-bound.stderr

@@ -36,7 +36,10 @@ error[E0433]: failed to resolve: use of undeclared type `I`
   --> $DIR/equality-bound.rs:9:41
    |
 LL | fn sum3<J: Iterator>(i: J) -> i32 where I::Item = i32 {
-   |                                         ^ use of undeclared type `I`
+   |                                         ^
+   |                                         |
+   |                                         use of undeclared type `I`
+   |                                         help: there is a type with a similar name: `J`
 
 error: aborting due to 4 previous errors
 

src/test/ui/pattern/pattern-error-continue.stderr

@@ -2,7 +2,10 @@ error[E0433]: failed to resolve: use of undeclared type `E`
   --> $DIR/pattern-error-continue.rs:33:9
    |
 LL |         E::V => {}
-   |         ^ use of undeclared type `E`
+   |         ^
+   |         |
+   |         use of undeclared type `E`
+   |         help: there is a type with a similar name: `Eq`
 
 error[E0532]: expected tuple struct or tuple variant, found unit variant `A::D`
   --> $DIR/pattern-error-continue.rs:18:9

src/test/ui/resolve/suggest-similar-type-name.rs

@@ -0,0 +1,10 @@
+struct FooType {}
+
+impl FooType {
+    fn bar() {}
+}
+
+fn main() {
+    FooTyp::bar()
+    //~^ ERROR failed to resolve: use of undeclared type `FooTyp`
+}

src/test/ui/resolve/suggest-similar-type-name.stderr

@@ -0,0 +1,12 @@
+error[E0433]: failed to resolve: use of undeclared type `FooTyp`
+  --> $DIR/suggest-similar-type-name.rs:8:5
+   |
+LL |     FooTyp::bar()
+   |     ^^^^^^
+   |     |
+   |     use of undeclared type `FooTyp`
+   |     help: there is a type with a similar name: `FooType`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0433`.