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bors 03a50ae9b8 Auto merge of #65188 - matthewjasper:stabilize-const-constructor, r=Centril 
Stabilize `const_constructor`

# Stabilization proposal

I propose that we stabilize `#![feature(const_constructor)]`.

Tracking issue: https://github.com/rust-lang/rust/issues/61456
Version target: 1.40 (2019-11-05 => beta, 2019-12-19 => stable).

## What is stabilized

### User guide

Tuple struct and tuple variant constructors are now considered to be constant functions. As such a call expression where the callee has a tuple struct or variant constructor "function item" type can be called:

```rust
const fn make_options() {
    // These already work because they are special cased:
    Some(0);
    (Option::Some)(1);
    // These also work now:
    let f = Option::Some;
    f(2);
    {Option::Some}(3);
    <Option<_>>::Some(5);
}
```

### Motivation

Consistency with other `const fn`. Consistency between syntactic path forms.

This should also ensure that constructors implement `const Fn` traits and can be coerced to `const fn` function pointers, if they are introduced.

## Tests

* [ui/consts/const_constructor/const-construct-call.rs](0d75ab2293/src/test/ui/consts/const_constructor/const-construct-call.rs) - Tests various syntactic forms, use in both `const fn` and `const` items, and constructors in both the current and extern crates.
* [ui/consts/const_constructor/const_constructor_qpath.rs](1850dfcdab/src/test/ui/consts/const_constructor/const_constructor_qpath.rs) - Tests that type qualified paths to enum variants are also considered to be `const fn`.(#64247)

r? @oli-obk

Closes #61456
Closes  #64247
2019-10-28 07:38:49 +00:00
..
ast libsyntax: Unconfigure tests during normal build 2019-08-02 01:59:01 +03:00
attr syntax/attr: reduce reliance on parser 2019-10-27 16:54:12 +01:00
diagnostics Replace diagnostic plugins with macro_rules 2019-09-05 12:35:15 -04:00
expand rustc, rustc_passes: don't depend on syntax_expand. 2019-10-27 17:05:57 +01:00
feature_gate Stabilize const_constructor 2019-10-27 21:25:35 +00:00
json Fix the start/end byte positions in the compiler JSON output 2019-10-21 19:28:29 +03:00
mut_visit Aggregation of cosmetic changes made during work on REPL PRs: libsyntax 2019-09-07 16:29:04 +01:00
parse Rollup merge of #65792 - Centril:split-syntax-2, r=petrochenkov 2019-10-28 04:53:07 +01:00
print syntax::parse::sess -> syntax::sess 2019-10-15 09:41:58 +02:00
source_map Apply suggestions from code review 2019-09-07 16:29:04 +01:00
tokenstream syntax_pos: NO_EXPANSION/SyntaxContext::empty() -> SyntaxContext::root() 2019-08-15 20:38:12 +03:00
util Rename Expr.node to Expr.kind 2019-09-26 18:21:09 +01:00
ast.rs libsyntax: Document ast module 2019-10-26 06:56:11 +03:00
build.rs Remove licenses 2018-12-25 21:08:33 -07:00
Cargo.toml remove bit_set re-export from rustc_data_structures 2019-09-29 16:11:30 +00:00
config.rs syntax/attr: reduce reliance on parser 2019-10-27 16:54:12 +01:00
early_buffered_lints.rs Warn if include macro fails to include entire file 2019-10-07 19:47:53 -04:00
entry.rs Rename Item.node to Item.kind 2019-09-26 18:21:48 +01:00
error_codes.rs Add long error explanation for E0584 2019-10-17 14:19:27 +02:00
json.rs Rollup merge of #65074 - Rantanen:json-byte-pos, r=matklad 2019-10-25 13:12:45 +02:00
lib.rs rustc, rustc_passes: don't depend on syntax_expand. 2019-10-27 17:05:57 +01:00
mut_visit.rs Remove the Option in TokenStream. 2019-10-14 09:14:39 +11:00
ptr.rs Remove many unnecessary trait derivations. 2019-10-21 20:59:18 +11:00
README.md rustc-guide has moved 2018-11-26 15:03:13 -06:00
sess.rs pre-expansion gate type_ascription 2019-10-24 00:32:03 +02:00
show_span.rs Rename rustc_errors dependency in rust 2018 crates 2019-02-13 00:28:52 +09:00
source_map.rs Rollup merge of #65074 - Rantanen:json-byte-pos, r=matklad 2019-10-25 13:12:45 +02:00
tests.rs Rollup merge of #65074 - Rantanen:json-byte-pos, r=matklad 2019-10-25 13:12:45 +02:00
tokenstream.rs Derive Rustc{En,De}codable for TokenStream. 2019-10-21 06:54:41 +11:00
visit.rs Rename ForeignItem.node to ForeignItem.kind 2019-09-26 18:21:48 +01:00

README.md

The syntax crate contains those things concerned purely with syntax – that is, the AST ("abstract syntax tree"), parser, pretty-printer, lexer, macro expander, and utilities for traversing ASTs.

For more information about how these things work in rustc, see the rustc guide: