Auto merge of #29260 - GuillaumeGomez:E0211_improvement, r=Manishearth

r? @Manishearth

cc #29248

Author: bors

src/librustc_typeck/diagnostics.rs

@@ -2348,24 +2348,80 @@ For information on the design of the orphan rules, see [RFC 1023].
 "##,
 
 E0211: r##"
-You used an intrinsic function which doesn't correspond to its
-definition. Erroneous code example:
+You used a function or type which doesn't fit the requirements for where it was
+used. Erroneous code examples:
 
 ```
 #![feature(intrinsics)]
 
 extern "rust-intrinsic" {
     fn size_of<T>(); // error: intrinsic has wrong type
 }
+
+// or:
+
+fn main() -> i32 { 0 }
+// error: main function expects type: `fn() {main}`: expected (), found i32
+
+// or:
+
+let x = 1u8;
+match x {
+    0u8...3i8 => (),
+    // error: mismatched types in range: expected u8, found i8
+    _ => ()
+}
+
+// or:
+
+use std::rc::Rc;
+struct Foo;
+
+impl Foo {
+    fn x(self: Rc<Foo>) {}
+    // error: mismatched self type: expected `Foo`: expected struct
+    //        `Foo`, found struct `alloc::rc::Rc`
+}
 ```
 
-Please check the function definition. Example:
+For the first code example, please check the function definition. Example:
 
 ```
 #![feature(intrinsics)]
 
 extern "rust-intrinsic" {
-    fn size_of<T>() -> usize;
+    fn size_of<T>() -> usize; // ok!
+}
+```
+
+The second case example is a bit particular : the main function must always
+have this definition:
+
+```
+fn main();
+```
+
+They never take parameters and never return types.
+
+For the third example, when you match, all patterns must have the same type
+as the type you're matching on. Example:
+
+```
+let x = 1u8;
+match x {
+    0u8...3u8 => (), // ok!
+    _ => ()
+}
+```
+
+And finally, for the last example, only `Box<Self>`, `&Self`, `Self`,
+or `&mut Self` work as explicit self parameters. Example:
+
+```
+struct Foo;
+
+impl Foo {
+    fn x(self: Box<Foo>) {} // ok!
 }
 ```
 "##,