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Add E0019 error explanation #26396

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Add E0019 error explanation #26396

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448779d
Add E0019 error explanation
GuillaumeGomez Jun 18, 2015
e6696dc
Remove unneeded indentation
GuillaumeGomez Jun 18, 2015
402ac99
Replace "Bad example" by a better sentence
GuillaumeGomez Jun 19, 2015
465b0db
Add const fn feature (thanks to @pnkfelix for signaling it to me!)
GuillaumeGomez Jun 19, 2015
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36 changes: 35 additions & 1 deletion src/librustc/diagnostics.rs
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Expand Up @@ -279,6 +279,41 @@ println!("{}", Y);
```
"##,

E0019: r##"
A function call isn't allowed in the const's initialization expression
because the expression's value must be known at compile-time. Bad example:
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The phrase "Bad example" is often used when one is saying that the example itself is bad -- i.e. when the example does not actually serve as a demonstration of the topic at hand.

I would instead write: "Example of erroneous code:" or "Example of non-compiling code:"

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I actually had the same comment on the other PRs I opened yesterday. I forgot to update this one, I do it.


```
enum Test {
V1
}

impl Test {
fn test(&self) -> i32 {
12
}
}

fn main() {
const FOO: Test = Test::V1;

const A: i32 = FOO.test(); // You can't call Test::func() here !
}
```

Remember: you can't use a function call inside a const's initialization
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You should add an additional paragraph about the const fn feature, which is currently feature-gated and thus only available in Nightly (but there are other error explanations like E0152 that reference feature-gated things). The sole purpose of const fn is to be a function call that breaks the rule you wrote here. :)

Here is a demonstration of const fn:

https://play.rust-lang.org/?gist=449fb78958b96eca7528&version=nightly

expression! However, you can totally use it elsewhere you want:

```
fn main() {
const FOO: Test = Test::V1;

FOO.func(); // here is good
let x = FOO.func(); // or even here!
}
```
"##,

E0020: r##"
This error indicates that an attempt was made to divide by zero (or take the
remainder of a zero divisor) in a static or constant expression.
Expand Down Expand Up @@ -952,7 +987,6 @@ static mut BAR: Option<Vec<i32>> = None;
register_diagnostics! {
E0016,
E0017,
E0019,
E0022,
E0038,
E0109,
Expand Down