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Auto merge of #49394 - cramertj:stable-match-bindings, r=nikomatsakis
Stabilize match_default_bindings This includes a submodule update to rustfmt in order to allow a stable feature declaration. r? @nikomatsakis cc #42640 Many of the tests this PR touches are merely testing the current lack of desired future behavior around #44849 and #44848 (cc @tschottdorf). I noticed the bullets for those items were checked on the tracking issue-- I've unchecked them, as they don't appear to have been completed and I don't see any comments indicating that we don't want to pursue them further. Still, I think it's fine to stabilize the current behavior, as I think expanding it in the future should be backwards-compatible.
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‎src/Cargo.lock

+24-24
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‎src/doc/unstable-book/src/language-features/match-default-bindings.md

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This file was deleted.

‎src/librustc/diagnostics.rs

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Original file line numberDiff line numberDiff line change
@@ -887,65 +887,6 @@ foo(3_i8);
887887
// therefore the type-checker complains with this error code.
888888
```
889889
890-
Here is a more subtle instance of the same problem, that can
891-
arise with for-loops in Rust:
892-
893-
```compile_fail
894-
let vs: Vec<i32> = vec![1, 2, 3, 4];
895-
for v in &vs {
896-
match v {
897-
1 => {},
898-
_ => {},
899-
}
900-
}
901-
```
902-
903-
The above fails because of an analogous type mismatch,
904-
though may be harder to see. Again, here are some
905-
explanatory comments for the same example:
906-
907-
```compile_fail
908-
{
909-
let vs = vec![1, 2, 3, 4];
910-
911-
// `for`-loops use a protocol based on the `Iterator`
912-
// trait. Each item yielded in a `for` loop has the
913-
// type `Iterator::Item` -- that is, `Item` is the
914-
// associated type of the concrete iterator impl.
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for v in &vs {
916-
// ~ ~~~
917-
// | |
918-
// | We borrow `vs`, iterating over a sequence of
919-
// | *references* of type `&Elem` (where `Elem` is
920-
// | vector's element type). Thus, the associated
921-
// | type `Item` must be a reference `&`-type ...
922-
// |
923-
// ... and `v` has the type `Iterator::Item`, as dictated by
924-
// the `for`-loop protocol ...
925-
926-
match v {
927-
1 => {}
928-
// ~
929-
// |
930-
// ... but *here*, `v` is forced to have some integral type;
931-
// only types like `u8`,`i8`,`u16`,`i16`, et cetera can
932-
// match the pattern `1` ...
933-
934-
_ => {}
935-
}
936-
937-
// ... therefore, the compiler complains, because it sees
938-
// an attempt to solve the equations
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// `some integral-type` = type-of-`v`
940-
// = `Iterator::Item`
941-
// = `&Elem` (i.e. `some reference type`)
942-
//
943-
// which cannot possibly all be true.
944-
945-
}
946-
}
947-
```
948-
949890
To avoid those issues, you have to make the types match correctly.
950891
So we can fix the previous examples like this:
951892

‎src/librustc/lib.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -55,7 +55,7 @@
5555
#![cfg_attr(stage0, feature(i128_type, i128))]
5656
#![cfg_attr(stage0, feature(inclusive_range_syntax))]
5757
#![cfg_attr(windows, feature(libc))]
58-
#![feature(match_default_bindings)]
58+
#![cfg_attr(stage0, feature(match_default_bindings))]
5959
#![feature(macro_lifetime_matcher)]
6060
#![feature(macro_vis_matcher)]
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#![feature(exhaustive_patterns)]

‎src/librustc_borrowck/lib.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -16,7 +16,7 @@
1616
#![allow(non_camel_case_types)]
1717

1818
#![feature(from_ref)]
19-
#![feature(match_default_bindings)]
19+
#![cfg_attr(stage0, feature(match_default_bindings))]
2020
#![feature(quote)]
2121

2222
#[macro_use] extern crate log;

‎src/librustc_mir/lib.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -30,7 +30,7 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
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#![cfg_attr(stage0, feature(i128_type))]
3131
#![cfg_attr(stage0, feature(inclusive_range_syntax))]
3232
#![feature(macro_vis_matcher)]
33-
#![feature(match_default_bindings)]
33+
#![cfg_attr(stage0, feature(match_default_bindings))]
3434
#![feature(exhaustive_patterns)]
3535
#![feature(range_contains)]
3636
#![feature(rustc_diagnostic_macros)]

‎src/librustc_traits/lib.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -14,7 +14,7 @@
1414
#![deny(warnings)]
1515

1616
#![feature(crate_visibility_modifier)]
17-
#![feature(match_default_bindings)]
17+
#![cfg_attr(stage0, feature(match_default_bindings))]
1818
#![feature(underscore_lifetimes)]
1919

2020
#[macro_use]

‎src/librustc_typeck/check/_match.rs

+4-37
Original file line numberDiff line numberDiff line change
@@ -23,7 +23,6 @@ use std::collections::hash_map::Entry::{Occupied, Vacant};
2323
use std::cmp;
2424
use syntax::ast;
2525
use syntax::codemap::Spanned;
26-
use syntax::feature_gate;
2726
use syntax::ptr::P;
2827
use syntax_pos::Span;
2928

@@ -114,42 +113,10 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
114113
}
115114
};
116115
if pat_adjustments.len() > 0 {
117-
if tcx.features().match_default_bindings {
118-
debug!("default binding mode is now {:?}", def_bm);
119-
self.inh.tables.borrow_mut()
120-
.pat_adjustments_mut()
121-
.insert(pat.hir_id, pat_adjustments);
122-
} else {
123-
let mut ref_sp = pat.span;
124-
let mut id = pat.id;
125-
loop { // make span include all enclosing `&` to avoid confusing diag output
126-
id = tcx.hir.get_parent_node(id);
127-
let node = tcx.hir.find(id);
128-
if let Some(hir::map::NodePat(pat)) = node {
129-
if let hir::PatKind::Ref(..) = pat.node {
130-
ref_sp = pat.span;
131-
} else {
132-
break;
133-
}
134-
} else {
135-
break;
136-
}
137-
}
138-
let sp = ref_sp.to(pat.span);
139-
let mut err = feature_gate::feature_err(
140-
&tcx.sess.parse_sess,
141-
"match_default_bindings",
142-
sp,
143-
feature_gate::GateIssue::Language,
144-
"non-reference pattern used to match a reference",
145-
);
146-
if let Ok(snippet) = tcx.sess.codemap().span_to_snippet(sp) {
147-
err.span_suggestion(sp,
148-
"consider using a reference",
149-
format!("&{}", &snippet));
150-
}
151-
err.emit();
152-
}
116+
debug!("default binding mode is now {:?}", def_bm);
117+
self.inh.tables.borrow_mut()
118+
.pat_adjustments_mut()
119+
.insert(pat.hir_id, pat_adjustments);
153120
}
154121
} else if let PatKind::Ref(..) = pat.node {
155122
// When you encounter a `&pat` pattern, reset to "by

‎src/librustc_typeck/lib.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -79,7 +79,7 @@ This API is completely unstable and subject to change.
7979
#![cfg_attr(stage0, feature(copy_closures, clone_closures))]
8080
#![feature(crate_visibility_modifier)]
8181
#![feature(from_ref)]
82-
#![feature(match_default_bindings)]
82+
#![cfg_attr(stage0, feature(match_default_bindings))]
8383
#![feature(exhaustive_patterns)]
8484
#![feature(option_filter)]
8585
#![feature(quote)]

‎src/libsyntax/feature_gate.rs

+2-3
Original file line numberDiff line numberDiff line change
@@ -385,9 +385,6 @@ declare_features! (
385385
// allow `'_` placeholder lifetimes
386386
(active, underscore_lifetimes, "1.22.0", Some(44524), None),
387387

388-
// Default match binding modes (RFC 2005)
389-
(active, match_default_bindings, "1.22.0", Some(42640), None),
390-
391388
// Trait object syntax with `dyn` prefix
392389
(active, dyn_trait, "1.22.0", Some(44662), Some(Edition::Edition2018)),
393390

@@ -563,6 +560,8 @@ declare_features! (
563560
(accepted, conservative_impl_trait, "1.26.0", Some(34511), None),
564561
// The `i128` type
565562
(accepted, i128_type, "1.26.0", Some(35118), None),
563+
// Default match binding modes (RFC 2005)
564+
(accepted, match_default_bindings, "1.26.0", Some(42640), None),
566565
);
567566

568567
// If you change this, please modify src/doc/unstable-book as well. You must

‎src/libsyntax/lib.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -22,7 +22,7 @@
2222

2323
#![feature(unicode)]
2424
#![feature(rustc_diagnostic_macros)]
25-
#![feature(match_default_bindings)]
25+
#![cfg_attr(stage0, feature(match_default_bindings))]
2626
#![feature(non_exhaustive)]
2727
#![cfg_attr(stage0, feature(i128_type))]
2828
#![feature(const_atomic_usize_new)]

‎src/test/compile-fail/issue-16338.rs

-1
Original file line numberDiff line numberDiff line change
@@ -17,5 +17,4 @@ fn main() {
1717
let Slice { data: data, len: len } = "foo";
1818
//~^ ERROR mismatched types
1919
//~| found type `Slice<_>`
20-
//~| ERROR non-reference pattern used to match a reference
2120
}

‎src/test/compile-fail/issue-20261.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,7 @@
1111
fn main() {
1212
// NB: this (almost) typechecks when default binding modes are enabled.
1313
for (ref i,) in [].iter() {
14-
//~^ ERROR non-reference pattern used to match a reference
1514
i.clone();
15+
//~^ ERROR type annotations needed
1616
}
1717
}

‎src/test/compile-fail/match-range-fail.rs

-2
Original file line numberDiff line numberDiff line change
@@ -15,15 +15,13 @@ fn main() {
1515
//~^^ ERROR only char and numeric types are allowed in range
1616
//~| start type: &'static str
1717
//~| end type: &'static str
18-
//~| ERROR non-reference pattern used to match a reference
1918

2019
match "wow" {
2120
10 ... "what" => ()
2221
};
2322
//~^^ ERROR only char and numeric types are allowed in range
2423
//~| start type: {integer}
2524
//~| end type: &'static str
26-
//~| ERROR non-reference pattern used to match a reference
2725

2826
match 5 {
2927
'c' ... 100 => { }

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