Rollup merge of rust-lang#61087 - estebank:parsepalooza, r=Centril

Tweak `self` arg not as first argument of a method diagnostic

Mention that `self` is only valid on "associated functions"
```
error: unexpected `self` argument in function
  --> $DIR/self-in-function-arg.rs:1:15
   |
LL | fn foo(x:i32, self: i32) -> i32 { self }
   |               ^^^^ not valid as function argument
   |
   = note: `self` is only valid as the first argument of an associated function
```

When it is a method, mention it must be first
```
error: unexpected `self` argument in function
  --> $DIR/trait-fn.rs:4:20
   |
LL |     fn c(foo: u32, self) {}
   |                    ^^^^ must be the first associated function argument
```

Move a bunch of error recovery methods to `diagnostics.rs` away from `parser.rs`.

Fix rust-lang#51547. CC rust-lang#60015.

src/test/ui/invalid-self-argument/bare-fn-start.rs

@@ -1,5 +1,6 @@
 fn a(&self) { }
-//~^ ERROR unexpected `self` argument in function
-//~| NOTE `self` is only valid as the first argument of an associated function
+//~^ ERROR unexpected `self` parameter in function
+//~| NOTE not valid as function parameter
+//~| NOTE `self` is only valid as the first parameter of an associated function
 
 fn main() { }

src/test/ui/invalid-self-argument/bare-fn-start.stderr

@@ -1,8 +1,10 @@
-error: unexpected `self` argument in function
-  --> $DIR/bare-fn-start.rs:1:7
+error: unexpected `self` parameter in function
+  --> $DIR/bare-fn-start.rs:1:6
    |
 LL | fn a(&self) { }
-   |       ^^^^ `self` is only valid as the first argument of an associated function
+   |      ^^^^^ not valid as function parameter
+   |
+   = note: `self` is only valid as the first parameter of an associated function
 
 error: aborting due to previous error
 

src/test/ui/invalid-self-argument/bare-fn.rs

@@ -1,5 +1,6 @@
 fn b(foo: u32, &mut self) { }
-//~^ ERROR unexpected `self` argument in function
-//~| NOTE `self` is only valid as the first argument of an associated function
+//~^ ERROR unexpected `self` parameter in function
+//~| NOTE not valid as function parameter
+//~| NOTE `self` is only valid as the first parameter of an associated function
 
 fn main() { }

src/test/ui/invalid-self-argument/bare-fn.stderr

@@ -1,8 +1,10 @@
-error: unexpected `self` argument in function
-  --> $DIR/bare-fn.rs:1:21
+error: unexpected `self` parameter in function
+  --> $DIR/bare-fn.rs:1:16
    |
 LL | fn b(foo: u32, &mut self) { }
-   |                     ^^^^ `self` is only valid as the first argument of an associated function
+   |                ^^^^^^^^^ not valid as function parameter
+   |
+   = note: `self` is only valid as the first parameter of an associated function
 
 error: aborting due to previous error
 

src/test/ui/invalid-self-argument/trait-fn.rs

@@ -2,8 +2,8 @@ struct Foo {}
 
 impl Foo {
     fn c(foo: u32, self) {}
-    //~^ ERROR unexpected `self` argument in function
-    //~| NOTE `self` is only valid as the first argument of an associated function
+    //~^ ERROR unexpected `self` parameter in function
+    //~| NOTE must be the first associated function parameter
 
     fn good(&mut self, foo: u32) {}
 }

src/test/ui/invalid-self-argument/trait-fn.stderr

@@ -1,8 +1,8 @@
-error: unexpected `self` argument in function
+error: unexpected `self` parameter in function
   --> $DIR/trait-fn.rs:4:20
    |
 LL |     fn c(foo: u32, self) {}
-   |                    ^^^^ `self` is only valid as the first argument of an associated function
+   |                    ^^^^ must be the first associated function parameter
 
 error: aborting due to previous error
 

src/test/ui/parser/self-in-function-arg.rs

@@ -0,0 +1,3 @@
+fn foo(x:i32, self: i32) -> i32 { self } //~ ERROR unexpected `self` parameter in function
+
+fn main() {}

src/test/ui/parser/self-in-function-arg.stderr

@@ -0,0 +1,10 @@
+error: unexpected `self` parameter in function
+  --> $DIR/self-in-function-arg.rs:1:15
+   |
+LL | fn foo(x:i32, self: i32) -> i32 { self }
+   |               ^^^^ not valid as function parameter
+   |
+   = note: `self` is only valid as the first parameter of an associated function
+
+error: aborting due to previous error
+