Auto merge of #38819 - GuillaumeGomez:main_func_wrong_type, r=GuillaumeGomez

Add a distinct error code and description for "main function has wron…

…g type"

src/test/compile-fail/E0580.rs

@@ -8,4 +8,4 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-fn main() -> i32 { 0 } //~ ERROR E0308
+fn main() -> i32 { 0 } //~ ERROR E0580

src/test/compile-fail/bad-main.rs

@@ -8,4 +8,4 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-fn main(x: isize) { } //~ ERROR: main function has wrong type
+fn main(x: isize) { } //~ ERROR: main function has wrong type [E0580]

src/test/compile-fail/extern-main-fn.rs

@@ -8,4 +8,4 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-extern fn main() {} //~ ERROR: main function has wrong type
+extern fn main() {} //~ ERROR: main function has wrong type [E0580]

src/test/compile-fail/main-wrong-type-2.rs

@@ -9,6 +9,6 @@
 // except according to those terms.
 
 fn main() -> char {
-//~^ ERROR: main function has wrong type
+//~^ ERROR: main function has wrong type [E0580]
     ' '
 }

src/test/compile-fail/main-wrong-type.rs

@@ -14,5 +14,5 @@ struct S {
 }
 
 fn main(foo: S) {
-//~^ ERROR: main function has wrong type
+//~^ ERROR: main function has wrong type [E0580]
 }