From e536e64702a12898ba7156c66de40b652ac21db1 Mon Sep 17 00:00:00 2001
From: Pramod Bisht <pramodpsb@outlook.com>
Date: Tue, 2 Oct 2018 05:51:02 +0000
Subject: [PATCH] Consolidate pattern check errors

we are consolidating `cannot bind by-move and by-ref in the same
pattern` message present on the different lines into single diagnostic
message.

To do this, we are first gathering those spans into the vector
after that we are throwing them with the help of MultiSpan in
a separate block.

Addresses: #53840
---
 src/librustc_mir/hair/pattern/check_match.rs | 34 ++++++++++++--------
 src/test/ui/issue-53840.rs                   | 27 ++++++++++++++++
 src/test/ui/issue-53840.stderr               | 20 ++++++++++++
 3 files changed, 67 insertions(+), 14 deletions(-)
 create mode 100644 src/test/ui/issue-53840.rs
 create mode 100644 src/test/ui/issue-53840.stderr

diff --git a/src/librustc_mir/hair/pattern/check_match.rs b/src/librustc_mir/hair/pattern/check_match.rs
index 6187e091319e0..f2ae5774da875 100644
--- a/src/librustc_mir/hair/pattern/check_match.rs
+++ b/src/librustc_mir/hair/pattern/check_match.rs
@@ -35,7 +35,7 @@ use std::slice;
 
 use syntax::ast;
 use syntax::ptr::P;
-use syntax_pos::{Span, DUMMY_SP};
+use syntax_pos::{Span, DUMMY_SP, MultiSpan};
 
 struct OuterVisitor<'a, 'tcx: 'a> { tcx: TyCtxt<'a, 'tcx, 'tcx> }
 
@@ -527,8 +527,8 @@ fn check_legality_of_move_bindings(cx: &MatchVisitor,
             }
         })
     }
-
-    let check_move = |p: &Pat, sub: Option<&Pat>| {
+    let span_vec = &mut Vec::new();
+    let check_move = |p: &Pat, sub: Option<&Pat>, span_vec: &mut Vec<Span>| {
         // check legality of moving out of the enum
 
         // x @ Foo(..) is legal, but x @ Foo(y) isn't.
@@ -546,16 +546,8 @@ fn check_legality_of_move_bindings(cx: &MatchVisitor,
                           crate attributes to enable");
             }
             err.emit();
-        } else if let Some(by_ref_span) = by_ref_span {
-            struct_span_err!(
-                cx.tcx.sess,
-                p.span,
-                E0009,
-                "cannot bind by-move and by-ref in the same pattern",
-            )
-            .span_label(p.span, "by-move pattern here")
-            .span_label(by_ref_span, "both by-ref and by-move used")
-            .emit();
+        } else if let Some(_by_ref_span) = by_ref_span {
+            span_vec.push(p.span);
         }
     };
 
@@ -567,7 +559,7 @@ fn check_legality_of_move_bindings(cx: &MatchVisitor,
                         ty::BindByValue(..) => {
                             let pat_ty = cx.tables.node_id_to_type(p.hir_id);
                             if pat_ty.moves_by_default(cx.tcx, cx.param_env, pat.span) {
-                                check_move(p, sub.as_ref().map(|p| &**p));
+                                check_move(p, sub.as_ref().map(|p| &**p), span_vec);
                             }
                         }
                         _ => {}
@@ -579,6 +571,20 @@ fn check_legality_of_move_bindings(cx: &MatchVisitor,
             true
         });
     }
+    if !span_vec.is_empty(){
+        let span = MultiSpan::from_spans(span_vec.clone());
+        let mut err = struct_span_err!(
+            cx.tcx.sess,
+            span,
+            E0009,
+            "cannot bind by-move and by-ref in the same pattern",
+        );
+        err.span_label(by_ref_span.unwrap(), "both by-ref and by-move used");
+        for span in span_vec.iter(){
+            err.span_label(*span, "by-move pattern here");
+        }
+        err.emit();
+    }
 }
 
 /// Ensures that a pattern guard doesn't borrow by mutable reference or
diff --git a/src/test/ui/issue-53840.rs b/src/test/ui/issue-53840.rs
new file mode 100644
index 0000000000000..ece3caf78e218
--- /dev/null
+++ b/src/test/ui/issue-53840.rs
@@ -0,0 +1,27 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+enum E {
+    Foo(String, String, String),
+}
+
+struct Bar {
+    a: String,
+    b: String,
+}
+
+fn main() {
+    let bar = Bar { a: "1".to_string(), b: "2".to_string() };
+    match E::Foo("".into(), "".into(), "".into()) {
+        E::Foo(a, b, ref c) => {}
+    }
+    match bar {
+        Bar {a, ref b} => {}
+    }
+}
diff --git a/src/test/ui/issue-53840.stderr b/src/test/ui/issue-53840.stderr
new file mode 100644
index 0000000000000..961e4c0ff6286
--- /dev/null
+++ b/src/test/ui/issue-53840.stderr
@@ -0,0 +1,20 @@
+error[E0009]: cannot bind by-move and by-ref in the same pattern
+  --> $DIR/issue-53840.rs:22:16
+   |
+LL |         E::Foo(a, b, ref c) => {}
+   |                ^  ^  ----- both by-ref and by-move used
+   |                |  |
+   |                |  by-move pattern here
+   |                by-move pattern here
+
+error[E0009]: cannot bind by-move and by-ref in the same pattern
+  --> $DIR/issue-53840.rs:25:14
+   |
+LL |         Bar {a, ref b} => {}
+   |              ^  ----- both by-ref and by-move used
+   |              |
+   |              by-move pattern here
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0009`.