Error E0019 is undocumented

[Michael-F-Bryan]

I was just playing with conditions in const functions and came across an error code (*E0019) which isn't yet documented in the error index.

(playground)

---

For example, trying to compile this:

#![feature(const_fn)]
const fn foo() -> u8 {
    if bar() == 1 { 5 } else { 3 }
}

const fn bar() -> u8 {
    1
}
fn main() {}

Gives you

 Compiling playground v0.0.1 (file:///playground)
error[E0019]: constant function contains unimplemented expression type
 --> src/main.rs:3:5
  |
3 |     if bar() == 1 { 5 } else { 3 }
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

error: Could not compile `playground`.

Where E0019 just sends you to the top of the page because the E0019 section doesn't exist.

---

What would be the best way for me to add an explanation of that error code to the compiler error index?

[kennytm]

This is a bug in the error index generator. E0019, along with many other error codes, are documented yet not included.

Duplicate of #42170 (E0493 missing — E0493 and E0019 live in the same file), which is closed in favor of #34588 (error index generator is fragile).

[Michael-F-Bryan]

Cheers @kennytm, I'll close this in favor of #34588 as well.