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doc/test: add UI test and reword docs for E0013 and E0015

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Ezra Shaw 2023-01-07 18:37:40 +13:00
parent 09382db78b
commit ae61c250cd
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5 changed files with 42 additions and 15 deletions
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23
compiler/rustc_error_codes/src/error_codes/E0015.md
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@ -1,5 +1,4 @@
A constant item was initialized with something that is not a constant
expression.
A non-`const` function was called in a `const` context.
Erroneous code example:
@ -8,26 +7,20 @@ fn create_some() -> Option<u8> {
Some(1)
}
const FOO: Option<u8> = create_some(); // error!
// error: cannot call non-const fn `create_some` in constants
const FOO: Option<u8> = create_some();
```
The only functions that can be called in static or constant expressions are
`const` functions, and struct/enum constructors.
All functions used in a `const` context (constant or static expression) must
be marked `const`.
To fix this error, you can declare `create_some` as a constant function:
```
const fn create_some() -> Option<u8> { // declared as a const function
// declared as a `const` function:
const fn create_some() -> Option<u8> {
Some(1)
}
const FOO: Option<u8> = create_some(); // ok!
// These are also working:
struct Bar {
x: u8,
}
const OTHER_FOO: Option<u8> = Some(1);
const BAR: Bar = Bar {x: 1};
const FOO: Option<u8> = create_some(); // no error!
```