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.

src/librustc/diagnostics.rs

@@ -887,65 +887,6 @@ foo(3_i8);
 // therefore the type-checker complains with this error code.
 ```
 
-Here is a more subtle instance of the same problem, that can
-arise with for-loops in Rust:
-
-```compile_fail
-let vs: Vec<i32> = vec![1, 2, 3, 4];
-for v in &vs {
-    match v {
-        1 => {},
-        _ => {},
-    }
-}
-```
-
-The above fails because of an analogous type mismatch,
-though may be harder to see. Again, here are some
-explanatory comments for the same example:
-
-```compile_fail
-{
-    let vs = vec![1, 2, 3, 4];
-
-    // `for`-loops use a protocol based on the `Iterator`
-    // trait. Each item yielded in a `for` loop has the
-    // type `Iterator::Item` -- that is, `Item` is the
-    // associated type of the concrete iterator impl.
-    for v in &vs {
-//      ~    ~~~
-//      |     |
-//      |    We borrow `vs`, iterating over a sequence of
-//      |    *references* of type `&Elem` (where `Elem` is
-//      |    vector's element type). Thus, the associated
-//      |    type `Item` must be a reference `&`-type ...
-//      |
-//  ... and `v` has the type `Iterator::Item`, as dictated by
-//  the `for`-loop protocol ...
-
-        match v {
-            1 => {}
-//          ~
-//          |
-// ... but *here*, `v` is forced to have some integral type;
-// only types like `u8`,`i8`,`u16`,`i16`, et cetera can
-// match the pattern `1` ...
-
-            _ => {}
-        }
-
-// ... therefore, the compiler complains, because it sees
-// an attempt to solve the equations
-// `some integral-type` = type-of-`v`
-//                      = `Iterator::Item`
-//                      = `&Elem` (i.e. `some reference type`)
-//
-// which cannot possibly all be true.
-
-    }
-}
-```
-
 To avoid those issues, you have to make the types match correctly.
 So we can fix the previous examples like this:
 

src/librustc/lib.rs

@@ -55,7 +55,7 @@
 #![cfg_attr(stage0, feature(i128_type, i128))]
 #![cfg_attr(stage0, feature(inclusive_range_syntax))]
 #![cfg_attr(windows, feature(libc))]
-#![feature(match_default_bindings)]
+#![cfg_attr(stage0, feature(match_default_bindings))]
 #![feature(macro_lifetime_matcher)]
 #![feature(macro_vis_matcher)]
 #![feature(exhaustive_patterns)]

src/librustc_borrowck/lib.rs

@@ -16,7 +16,7 @@
 #![allow(non_camel_case_types)]
 
 #![feature(from_ref)]
-#![feature(match_default_bindings)]
+#![cfg_attr(stage0, feature(match_default_bindings))]
 #![feature(quote)]
 
 #[macro_use] extern crate log;

src/librustc_mir/lib.rs

@@ -30,7 +30,7 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 #![cfg_attr(stage0, feature(i128_type))]
 #![cfg_attr(stage0, feature(inclusive_range_syntax))]
 #![feature(macro_vis_matcher)]
-#![feature(match_default_bindings)]
+#![cfg_attr(stage0, feature(match_default_bindings))]
 #![feature(exhaustive_patterns)]
 #![feature(range_contains)]
 #![feature(rustc_diagnostic_macros)]

src/librustc_traits/lib.rs

@@ -14,7 +14,7 @@
 #![deny(warnings)]
 
 #![feature(crate_visibility_modifier)]
-#![feature(match_default_bindings)]
+#![cfg_attr(stage0, feature(match_default_bindings))]
 #![feature(underscore_lifetimes)]
 
 #[macro_use]

src/librustc_typeck/check/_match.rs

@@ -23,7 +23,6 @@ use std::collections::hash_map::Entry::{Occupied, Vacant};
 use std::cmp;
 use syntax::ast;
 use syntax::codemap::Spanned;
-use syntax::feature_gate;
 use syntax::ptr::P;
 use syntax_pos::Span;
 
@@ -114,42 +113,10 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 }
             };
             if pat_adjustments.len() > 0 {
-                if tcx.features().match_default_bindings {
-                    debug!("default binding mode is now {:?}", def_bm);
-                    self.inh.tables.borrow_mut()
-                        .pat_adjustments_mut()
-                        .insert(pat.hir_id, pat_adjustments);
-                } else {
-                    let mut ref_sp = pat.span;
-                    let mut id = pat.id;
-                    loop {  // make span include all enclosing `&` to avoid confusing diag output
-                        id = tcx.hir.get_parent_node(id);
-                        let node = tcx.hir.find(id);
-                        if let Some(hir::map::NodePat(pat)) = node {
-                            if let hir::PatKind::Ref(..) = pat.node {
-                                ref_sp = pat.span;
-                            } else {
-                                break;
-                            }
-                        } else {
-                            break;
-                        }
-                    }
-                    let sp = ref_sp.to(pat.span);
-                    let mut err = feature_gate::feature_err(
-                        &tcx.sess.parse_sess,
-                        "match_default_bindings",
-                        sp,
-                        feature_gate::GateIssue::Language,
-                        "non-reference pattern used to match a reference",
-                    );
-                    if let Ok(snippet) = tcx.sess.codemap().span_to_snippet(sp) {
-                        err.span_suggestion(sp,
-                                            "consider using a reference",
-                                            format!("&{}", &snippet));
-                    }
-                    err.emit();
-                }
+                debug!("default binding mode is now {:?}", def_bm);
+                self.inh.tables.borrow_mut()
+                    .pat_adjustments_mut()
+                    .insert(pat.hir_id, pat_adjustments);
             }
         } else if let PatKind::Ref(..) = pat.node {
             // When you encounter a `&pat` pattern, reset to "by

src/librustc_typeck/lib.rs

@@ -79,7 +79,7 @@ This API is completely unstable and subject to change.
 #![cfg_attr(stage0, feature(copy_closures, clone_closures))]
 #![feature(crate_visibility_modifier)]
 #![feature(from_ref)]
-#![feature(match_default_bindings)]
+#![cfg_attr(stage0, feature(match_default_bindings))]
 #![feature(exhaustive_patterns)]
 #![feature(option_filter)]
 #![feature(quote)]

src/libsyntax/feature_gate.rs

@@ -385,9 +385,6 @@ declare_features! (
     // allow `'_` placeholder lifetimes
     (active, underscore_lifetimes, "1.22.0", Some(44524), None),
 
-    // Default match binding modes (RFC 2005)
-    (active, match_default_bindings, "1.22.0", Some(42640), None),
-
     // Trait object syntax with `dyn` prefix
     (active, dyn_trait, "1.22.0", Some(44662), Some(Edition::Edition2018)),
 
@@ -563,6 +560,8 @@ declare_features! (
     (accepted, conservative_impl_trait, "1.26.0", Some(34511), None),
     // The `i128` type
     (accepted, i128_type, "1.26.0", Some(35118), None),
+    // Default match binding modes (RFC 2005)
+    (accepted, match_default_bindings, "1.26.0", Some(42640), None),
 );
 
 // If you change this, please modify src/doc/unstable-book as well. You must

src/libsyntax/lib.rs

@@ -22,7 +22,7 @@
 
 #![feature(unicode)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(match_default_bindings)]
+#![cfg_attr(stage0, feature(match_default_bindings))]
 #![feature(non_exhaustive)]
 #![cfg_attr(stage0, feature(i128_type))]
 #![feature(const_atomic_usize_new)]

src/test/compile-fail/issue-16338.rs

@@ -17,5 +17,4 @@ fn main() {
     let Slice { data: data, len: len } = "foo";
     //~^ ERROR mismatched types
     //~| found type `Slice<_>`
-    //~| ERROR non-reference pattern used to match a reference
 }

src/test/compile-fail/issue-20261.rs

@@ -11,7 +11,7 @@
 fn main() {
     // NB: this (almost) typechecks when default binding modes are enabled.
     for (ref i,) in [].iter() {
-        //~^ ERROR non-reference pattern used to match a reference
         i.clone();
+        //~^ ERROR type annotations needed
     }
 }

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

@@ -15,15 +15,13 @@ fn main() {
     //~^^ ERROR only char and numeric types are allowed in range
     //~| start type: &'static str
     //~| end type: &'static str
-    //~| ERROR non-reference pattern used to match a reference
 
     match "wow" {
         10 ... "what" => ()
     };
     //~^^ ERROR only char and numeric types are allowed in range
     //~| start type: {integer}
     //~| end type: &'static str
-    //~| ERROR non-reference pattern used to match a reference
 
     match 5 {
         'c' ... 100 => { }