Add point-at-inference ui test for wrong arity case

Author: martingms

tests/ui/type/type-check/point-at-inference-4.rs

@@ -0,0 +1,23 @@
+struct S<A, B>(Option<(A, B)>);
+
+impl<A, B> S<A, B> {
+    fn infer(&self, a: A, b: B) {}
+    //~^ NOTE associated function defined here
+    //~| NOTE
+    //~| NOTE
+}
+
+fn main() {
+    let s = S(None);
+    s.infer(0i32);
+    //~^ ERROR this method takes 2 arguments but 1 argument was supplied
+    //~| NOTE an argument is missing
+    //~| HELP provide the argument
+    //~| NOTE this is of type `i32`, which causes `s` to be inferred as `S<i32, _>`
+    //~| HELP change the type of the numeric literal from `i32` to `u32`
+    let t: S<u32, _> = s;
+    //~^ ERROR mismatched types
+    //~| NOTE expected `S<u32, _>`, found `S<i32, _>`
+    //~| NOTE expected due to this
+    //~| NOTE expected struct `S<u32, _>`
+}

tests/ui/type/type-check/point-at-inference-4.stderr

@@ -0,0 +1,38 @@
+error[E0061]: this method takes 2 arguments but 1 argument was supplied
+  --> $DIR/point-at-inference-4.rs:12:7
+   |
+LL |     s.infer(0i32);
+   |       ^^^^^------ an argument is missing
+   |
+note: associated function defined here
+  --> $DIR/point-at-inference-4.rs:4:8
+   |
+LL |     fn infer(&self, a: A, b: B) {}
+   |        ^^^^^        ----  ----
+help: provide the argument
+   |
+LL |     s.infer(0i32, /* b */);
+   |            ~~~~~~~~~~~~~~~
+
+error[E0308]: mismatched types
+  --> $DIR/point-at-inference-4.rs:18:24
+   |
+LL |     s.infer(0i32);
+   |             ---- this is of type `i32`, which causes `s` to be inferred as `S<i32, _>`
+...
+LL |     let t: S<u32, _> = s;
+   |            ---------   ^ expected `S<u32, _>`, found `S<i32, _>`
+   |            |
+   |            expected due to this
+   |
+   = note: expected struct `S<u32, _>`
+              found struct `S<i32, _>`
+help: change the type of the numeric literal from `i32` to `u32`
+   |
+LL |     s.infer(0u32);
+   |              ~~~
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0061, E0308.
+For more information about an error, try `rustc --explain E0061`.