Split up very long message

This should make it easier to read.

6 files changed, 44 insertions, 36 deletions

diff --git a/compiler/rustc_typeck/src/check/op.rs b/compiler/rustc_typeck/src/check/op.rs
index 838f8b0a61d..8bb0613f456 100644
--- a/compiler/rustc_typeck/src/check/op.rs
+++ b/compiler/rustc_typeck/src/check/op.rs
@@ -549,15 +549,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         is_assign: IsAssign,
         op: hir::BinOp,
     ) -> bool {
-        let remove_borrow_msg = "String concatenation appends the string on the right to the \
-                                 string on the left and may require reallocation. This \
-                                 requires ownership of the string on the left";
-
-        let msg = "`to_owned()` can be used to create an owned `String` \
-                   from a string reference. String concatenation \
-                   appends the string on the right to the string \
-                   on the left and may require reallocation. This \
-                   requires ownership of the string on the left";
+        let str_concat_note = "String concatenation appends the string on the right to the \
+                                    string on the left and may require reallocation. This \
+                                    requires ownership of the string on the left.";
+        let rm_borrow_msg = "remove the borrow to obtain an owned `String`";
+        let to_owned_msg = "use `to_owned()` to create an owned `String` from a string reference";
 
         let string_type = self.tcx.get_diagnostic_item(sym::String);
         let is_std_string = |ty: Ty<'tcx>| match ty.ty_adt_def() {
@@ -574,17 +570,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             {
                 if let IsAssign::No = is_assign { // Do not supply this message if `&str += &str`
                     err.span_label(op.span, "`+` cannot be used to concatenate two `&str` strings");
+                    err.note(str_concat_note);
                     if let hir::ExprKind::AddrOf(_,_,lhs_inner_expr) = lhs_expr.kind {
                         err.span_suggestion(
                             lhs_expr.span.until(lhs_inner_expr.span),
-                            remove_borrow_msg,
+                            rm_borrow_msg,
                             "".to_owned(),
                             Applicability::MachineApplicable
                         );
                     } else {
                         err.span_suggestion(
                             lhs_expr.span.shrink_to_hi(),
-                            msg,
+                            to_owned_msg,
                             ".to_owned()".to_owned(),
                             Applicability::MachineApplicable
                         );
@@ -601,18 +598,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 );
                 match is_assign {
                     IsAssign::No => {
+                        let sugg_msg;
+                        let lhs_sugg = if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
+                            sugg_msg = "remove the borrow on the left and add one on the right";
+                            (lhs_expr.span.until(lhs_inner_expr.span), "".to_owned())
+                        } else {
+                            sugg_msg = "call `.to_owned()` on the left and add a borrow on the right";
+                            (lhs_expr.span.shrink_to_hi(), ".to_owned()".to_owned())
+                        };
                         let suggestions = vec![
-                            if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
-                                (lhs_expr.span.until(lhs_inner_expr.span), "".to_owned())
-                            } else {
-                                (lhs_expr.span.shrink_to_hi(), ".to_owned()".to_owned())
-                            },
+                            lhs_sugg,
                             (rhs_expr.span.shrink_to_lo(), "&".to_owned()),
                         ];
-                        err.multipart_suggestion(msg, suggestions, Applicability::MachineApplicable);
+                        err.multipart_suggestion(sugg_msg, suggestions, Applicability::MachineApplicable);
                     }
                     IsAssign::Yes => {
-                        err.help(msg);
+                        err.note(str_concat_note);
                     }
                 }
                 true
diff --git a/src/test/ui/issues/issue-47377.stderr b/src/test/ui/issues/issue-47377.stderr
index 2c17a19779f..2e00de84087 100644
--- a/src/test/ui/issues/issue-47377.stderr
+++ b/src/test/ui/issues/issue-47377.stderr
@@ -7,7 +7,8 @@ LL |      let _a = b + ", World!";
    |               | `+` cannot be used to concatenate two `&str` strings
    |               &str
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   = note: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left.
+help: use `to_owned()` to create an owned `String` from a string reference
    |
 LL |      let _a = b.to_owned() + ", World!";
    |                +++++++++++
diff --git a/src/test/ui/issues/issue-47380.stderr b/src/test/ui/issues/issue-47380.stderr
index 417206e6cc4..fec64009444 100644
--- a/src/test/ui/issues/issue-47380.stderr
+++ b/src/test/ui/issues/issue-47380.stderr
@@ -7,7 +7,8 @@ LL |     println!("🦀🦀🦀🦀🦀"); let _a = b + ", World!";
    |                                      | `+` cannot be used to concatenate two `&str` strings
    |                                      &str
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   = note: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left.
+help: use `to_owned()` to create an owned `String` from a string reference
    |
 LL |     println!("🦀🦀🦀🦀🦀"); let _a = b.to_owned() + ", World!";
    |                                       +++++++++++
diff --git a/src/test/ui/span/issue-39018.stderr b/src/test/ui/span/issue-39018.stderr
index 444d037571e..9054dd931ca 100644
--- a/src/test/ui/span/issue-39018.stderr
+++ b/src/test/ui/span/issue-39018.stderr
@@ -7,7 +7,8 @@ LL |     let x = "Hello " + "World!";
    |             |        `+` cannot be used to concatenate two `&str` strings
    |             &str
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   = note: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left.
+help: use `to_owned()` to create an owned `String` from a string reference
    |
 LL |     let x = "Hello ".to_owned() + "World!";
    |                     +++++++++++
@@ -46,7 +47,7 @@ LL |     let x = "Hello " + "World!".to_owned();
    |             |        `+` cannot be used to concatenate a `&str` with a `String`
    |             &str
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+help: call `.to_owned()` on the left and add a borrow on the right
    |
 LL |     let x = "Hello ".to_owned() + &"World!".to_owned();
    |                     +++++++++++   +
@@ -59,12 +60,9 @@ LL |     let _ = &a + &b;
    |             |  |
    |             |  `+` cannot be used to concatenate two `&str` strings
    |             &String
+   |             help: remove the borrow to obtain an owned `String`
    |
-help: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
-   |
-LL -     let _ = &a + &b;
-LL +     let _ = a + &b;
-   | 
+   = note: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left.
 
 error[E0369]: cannot add `String` to `&String`
   --> $DIR/issue-39018.rs:27:16
@@ -75,7 +73,7 @@ LL |     let _ = &a + b;
    |             |  `+` cannot be used to concatenate a `&str` with a `String`
    |             &String
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+help: remove the borrow on the left and add one on the right
    |
 LL -     let _ = &a + b;
 LL +     let _ = a + &b;
@@ -99,7 +97,7 @@ LL |     let _ = e + b;
    |             | `+` cannot be used to concatenate a `&str` with a `String`
    |             &String
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+help: call `.to_owned()` on the left and add a borrow on the right
    |
 LL |     let _ = e.to_owned() + &b;
    |              +++++++++++   +
@@ -113,7 +111,8 @@ LL |     let _ = e + &b;
    |             | `+` cannot be used to concatenate two `&str` strings
    |             &String
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   = note: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left.
+help: use `to_owned()` to create an owned `String` from a string reference
    |
 LL |     let _ = e.to_owned() + &b;
    |              +++++++++++
@@ -127,7 +126,8 @@ LL |     let _ = e + d;
    |             | `+` cannot be used to concatenate two `&str` strings
    |             &String
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   = note: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left.
+help: use `to_owned()` to create an owned `String` from a string reference
    |
 LL |     let _ = e.to_owned() + d;
    |              +++++++++++
@@ -141,7 +141,8 @@ LL |     let _ = e + &d;
    |             | `+` cannot be used to concatenate two `&str` strings
    |             &String
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   = note: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left.
+help: use `to_owned()` to create an owned `String` from a string reference
    |
 LL |     let _ = e.to_owned() + &d;
    |              +++++++++++
@@ -171,7 +172,8 @@ LL |     let _ = c + &d;
    |             | `+` cannot be used to concatenate two `&str` strings
    |             &str
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   = note: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left.
+help: use `to_owned()` to create an owned `String` from a string reference
    |
 LL |     let _ = c.to_owned() + &d;
    |              +++++++++++
@@ -185,7 +187,8 @@ LL |     let _ = c + d;
    |             | `+` cannot be used to concatenate two `&str` strings
    |             &str
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   = note: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left.
+help: use `to_owned()` to create an owned `String` from a string reference
    |
 LL |     let _ = c.to_owned() + d;
    |              +++++++++++
diff --git a/src/test/ui/str/str-concat-on-double-ref.stderr b/src/test/ui/str/str-concat-on-double-ref.stderr
index cc9456be901..e8b5c2bbd85 100644
--- a/src/test/ui/str/str-concat-on-double-ref.stderr
+++ b/src/test/ui/str/str-concat-on-double-ref.stderr
@@ -7,7 +7,8 @@ LL |     let c = a + b;
    |             | `+` cannot be used to concatenate two `&str` strings
    |             &String
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   = note: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left.
+help: use `to_owned()` to create an owned `String` from a string reference
    |
 LL |     let c = a.to_owned() + b;
    |              +++++++++++
diff --git a/src/test/ui/terminal-width/non-1-width-unicode-multiline-label.stderr b/src/test/ui/terminal-width/non-1-width-unicode-multiline-label.stderr
index 2da3db4a7fa..72005a88980 100644
--- a/src/test/ui/terminal-width/non-1-width-unicode-multiline-label.stderr
+++ b/src/test/ui/terminal-width/non-1-width-unicode-multiline-label.stderr
@@ -7,7 +7,8 @@ LL | ...ཽཾཿ྄ཱྀྀྂྃ྅྆྇ྈྉྊྋྌྍྎྏྐྑྒྒྷྔ
    |                                                  |              `+` cannot be used to concatenate two `&str` strings
    |                                                  &str
    |
-help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   = note: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left.
+help: use `to_owned()` to create an owned `String` from a string reference
    |
 LL |     let _ = "ༀ༁༂༃༄༅༆༇༈༉༊་༌།༎༏༐༑༒༓༔༕༖༗༘༙༚༛༜༝༞༟༠༡༢༣༤༥༦༧༨༩༪༫༬༭༮༯༰༱༲༳༴༵༶༷༸༹༺༻༼༽༾༿ཀཁགགྷངཅཆཇ཈ཉཊཋཌཌྷཎཏཐདདྷནཔཕབབྷམཙཚཛཛྷཝཞཟའཡརལཤཥསཧཨཀྵཪཫཬ཭཮཯཰ཱཱཱིིུུྲྀཷླྀཹེཻོཽཾཿ྄ཱྀྀྂྃ྅྆྇ྈྉྊྋྌྍྎྏྐྑྒྒྷྔྕྖྗ྘ྙྚྛྜྜྷྞྟྠྡྡྷྣྤྥྦྦྷྨྩྪྫྫྷྭྮྯྰྱྲླྴྵྶྷྸྐྵྺྻྼ྽྾྿࿀࿁࿂࿃࿄࿅࿆࿇࿈࿉࿊࿋࿌࿍࿎࿏࿐࿑࿒࿓࿔࿕࿖࿗࿘࿙࿚"; let _a = unicode_is_fun.to_owned() + " really fun!";
    |                                                                                                                                                                                         +++++++++++