remove support for the #[start] attribute

compiler/rustc_error_codes/src/error_codes/E0132.md

@@ -1,32 +1,3 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 A function with the `start` attribute was declared with type parameters.
-
-Erroneous code example:
-
-```compile_fail,E0132
-#![feature(start)]
-
-#[start]
-fn f<T>() {}
-```
-
-It is not possible to declare type parameters on a function that has the `start`
-attribute. Such a function must have the following type signature (for more
-information, view [the unstable book][1]):
-
-[1]: https://doc.rust-lang.org/unstable-book/language-features/start.html
-
-```
-# let _:
-fn(isize, *const *const u8) -> isize;
-```
-
-Example:
-
-```
-#![feature(start)]
-
-#[start]
-fn my_start(argc: isize, argv: *const *const u8) -> isize {
-    0
-}
-```

compiler/rustc_error_codes/src/error_codes/E0138.md

@@ -1,25 +1,3 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 More than one function was declared with the `#[start]` attribute.
-
-Erroneous code example:
-
-```compile_fail,E0138
-#![feature(start)]
-
-#[start]
-fn foo(argc: isize, argv: *const *const u8) -> isize {}
-
-#[start]
-fn f(argc: isize, argv: *const *const u8) -> isize {}
-// error: multiple 'start' functions
-```
-
-This error indicates that the compiler found multiple functions with the
-`#[start]` attribute. This is an error because there must be a unique entry
-point into a Rust program. Example:
-
-```
-#![feature(start)]
-
-#[start]
-fn foo(argc: isize, argv: *const *const u8) -> isize { 0 } // ok!
-```

compiler/rustc_error_codes/src/error_codes/E0647.md

@@ -1,13 +1,3 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 The `start` function was defined with a where clause.
-
-Erroneous code example:
-
-```compile_fail,E0647
-#![feature(start)]
-
-#[start]
-fn start(_: isize, _: *const *const u8) -> isize where (): Copy {
-    //^ error: `#[start]` function is not allowed to have a where clause
-    0
-}
-```

compiler/rustc_error_codes/src/lib.rs

@@ -24,6 +24,10 @@
 //
 // Both columns are necessary because it's not possible in Rust to create a new identifier such as
 // `E0123` from an integer literal such as `0123`, unfortunately.
+//
+// Do *not* remove entries from this list. Instead, just add a note th the corresponding markdown
+// file saying that this error is not emitted by the compiler any more (see E0001.md for an
+// example), and remove all code examples that do not build any more.
 #[macro_export]
 macro_rules! error_codes {
     ($macro:path) => (