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Don't recommend const fns on a stable build without a note about nightlies

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Fixes #28490
This commit is contained in:
Manish Goregaokar 2015-09-19 09:29:04 +05:30
parent 6e5a325474
commit dcf49b5f68
2 changed files with 26 additions and 6 deletions
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12
src/librustc/diagnostics.rs
View file

@ -298,10 +298,18 @@ const FOO: i32 = { 0 }; // but brackets are useless here
```
"##,
// FIXME(#24111) Change the language here when const fn stabilizes
E0015: r##"
The only functions that can be called in static or constant expressions are
`const` functions. Rust currently does not support more general compile-time
function execution.
`const` functions, and struct/enum constructors. `const` functions are only
available on a nightly compiler. Rust currently does not support more general
compile-time function execution.
```
const FOO: Option<u8> = Some(1); // enum constructor
struct Bar {x: u8}
const BAR: Bar = Bar {x: 1}; // struct constructor
```
See [RFC 911] for more details on the design of `const fn`s.

20
src/librustc/middle/check_const.rs
View file

@ -39,6 +39,7 @@ use util::nodemap::NodeMap;
use rustc_front::hir;
use syntax::ast;
use syntax::codemap::Span;
use syntax::feature_gate::UnstableFeatures;
use rustc_front::visit::{self, FnKind, Visitor};
use std::collections::hash_map::Entry;
@ -709,10 +710,21 @@ fn check_expr<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>,
if !is_const {
v.add_qualif(ConstQualif::NOT_CONST);
if v.mode != Mode::Var {
span_err!(v.tcx.sess, e.span, E0015,
"function calls in {}s are limited to \
constant functions, \
struct and enum constructors", v.msg());
// FIXME(#24111) Remove this check when const fn stabilizes
if let UnstableFeatures::Disallow = v.tcx.sess.opts.unstable_features {
span_err!(v.tcx.sess, e.span, E0015,
"function calls in {}s are limited to \
struct and enum constructors", v.msg());
v.tcx.sess.span_note(e.span,
"a limited form of compile-time function \
evaluation is available on a nightly \
compiler via `const fn`");
} else {
span_err!(v.tcx.sess, e.span, E0015,
"function calls in {}s are limited to \
constant functions, \
struct and enum constructors", v.msg());
}
}
}
}