Use get_parent_node instead of using spans

src/librustc_typeck/check/_match.rs

@@ -23,9 +23,7 @@ use std::collections::hash_map::Entry::{Occupied, Vacant};
 use std::cmp;
 use syntax::ast;
 use syntax::codemap::Spanned;
-use syntax::errors::DiagnosticBuilder;
 use syntax::feature_gate;
-use syntax::parse::ParseSess;
 use syntax::ptr::P;
 use syntax_pos::Span;
 
@@ -122,32 +120,35 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                         .pat_adjustments_mut()
                         .insert(pat.hir_id, pat_adjustments);
                 } else {
-                    fn feature_err<'a>(sp: Span, sess: &'a ParseSess) -> DiagnosticBuilder<'a> {
-                        feature_gate::feature_err(
-                            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(pat.span) {
-                        // The following is a bit of a hack. We probably should check the AST for
-                        // this instead, but this should be good enough for the expected cases.
-                        let prev_span = pat.span.prev_point();
-                        let (sp, sugg) = match tcx.sess.codemap().span_to_snippet(prev_span) {
-                            // Make the suggestion more obvious when having `&(_, _)`
-                            Ok(ref prev) if &*prev == "&" => {
-                                (prev_span.to(pat.span), format!("&&{}", &snippet)),
+                    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;
                             }
-                            _ => (pat.span, format!("&{}", &snippet)),
-                        };
-                        let mut err = feature_err(sp, &tcx.sess.parse_sess);
-                        err.span_suggestion(sp, "consider using a reference", sugg);
-                        err.emit();
-                    } else {
-                        feature_err(pat.span, &tcx.sess.parse_sess).emit();
+                        } 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();
                 }
             }
         }

src/libsyntax_pos/lib.rs

@@ -159,18 +159,6 @@ impl Span {
         Span::new(BytePos(lo), BytePos(lo), span.ctxt)
     }
 
-    /// Returns a new span representing the previous character after the start-point of this span
-    pub fn prev_point(self) -> Span {
-        let span = self.data();
-        let span_lo = span.lo.0;
-        let lo = if span_lo == 0 {
-            0
-        } else {
-            span_lo - 1
-        };
-        Span::new(BytePos(lo), BytePos(span_lo), span.ctxt)
-    }
-
     /// Returns `self` if `self` is not the dummy span, and `other` otherwise.
     pub fn substitute_dummy(self, other: Span) -> Span {
         if self.source_equal(&DUMMY_SP) { other } else { self }

src/test/ui/rfc-2005-default-binding-mode/suggestion.stderr

@@ -2,7 +2,7 @@ error: non-reference pattern used to match a reference (see issue #42640)
   --> $DIR/suggestion.rs:12:12
    |
 12 |     if let Some(y) = &Some(22) { //~ ERROR non-reference pattern
-   |            ^^^^^^^ help: consider using: `&Some(y)`
+   |            ^^^^^^^ help: consider using a reference: `&Some(y)`
    |
    = help: add #![feature(match_default_bindings)] to the crate attributes to enable
 

src/test/ui/suggestions/dont-suggest-dereference-on-arg.stderr

@@ -1,8 +1,8 @@
 error: non-reference pattern used to match a reference (see issue #42640)
-  --> dont-suggest-dereference-on-arg.rs:16:19
+  --> $DIR/dont-suggest-dereference-on-arg.rs:16:19
    |
 16 |         .filter(|&(ref a, _)| foo(a))
-   |                  ^^^^^^^^^^^ help: consider using: `&&(ref k, _)`
+   |                  ^^^^^^^^^^^ help: consider using a reference: `&&(ref k, _)`
    |
    = help: add #![feature(match_default_bindings)] to the crate attributes to enable