Use a common subdiagnostic format for generic borrows

This is setup for unifing the logic for suggestions to borrow arguments in generic positions.
As of this commit, it's still special cases for `AsRef`/`Borrow`-like traits and `Fn`-like traits.

Author: dianne

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -478,7 +478,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                         return;
                     }
 
-                    let mut is_mut = false;
+                    let mut mutbl = ty::Mutability::Not;
                     if let Some(param) = arg_param
                         && self
                             .infcx
@@ -504,7 +504,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                                     ]
                                     .contains(&Some(predicate.def_id()))
                                     {
-                                        is_mut = true;
+                                        mutbl = ty::Mutability::Mut;
                                     }
                                     true
                                 } else {
@@ -514,13 +514,18 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                     {
                         // The type of the argument corresponding to the expression that got moved
                         // is a type parameter `T`, which is has a `T: AsRef` obligation.
+                        let place_desc = if let Some(desc) = self.describe_place(moved_place) {
+                            format!("`{desc}`")
+                        } else {
+                            "here".to_owned()
+                        };
                         err.span_suggestion_verbose(
                             expr.span.shrink_to_lo(),
-                            "borrow the value to avoid moving it",
-                            format!("&{}", if is_mut { "mut " } else { "" }),
+                            format!("consider {}borrowing {place_desc}", mutbl.mutably_str()),
+                            mutbl.ref_prefix_str(),
                             Applicability::MaybeIncorrect,
                         );
-                        can_suggest_clone = is_mut;
+                        can_suggest_clone = mutbl.is_mut();
                     } else if let Some(local_def_id) = def_id.as_local()
                         && let node = self.infcx.tcx.hir_node_by_def_id(local_def_id)
                         && let Some(fn_decl) = node.fn_decl()

tests/ui/moves/moved-value-on-as-ref-arg.stderr

@@ -8,7 +8,7 @@ LL |     foo(bar);
 LL |     let _baa = bar;
    |                ^^^ value used here after move
    |
-help: borrow the value to avoid moving it
+help: consider borrowing `bar`
    |
 LL |     foo(&bar);
    |         +
@@ -31,7 +31,7 @@ LL | struct Bar;
 ...
 LL |     qux(bar);
    |         --- you could clone this value
-help: borrow the value to avoid moving it
+help: consider mutably borrowing `bar`
    |
 LL |     qux(&mut bar);
    |         ++++
@@ -46,7 +46,7 @@ LL |     bat(bar);
 LL |     let _baa = bar;
    |                ^^^ value used here after move
    |
-help: borrow the value to avoid moving it
+help: consider borrowing `bar`
    |
 LL |     bat(&bar);
    |         +
@@ -69,7 +69,7 @@ LL | struct Bar;
 ...
 LL |     baz(bar);
    |         --- you could clone this value
-help: borrow the value to avoid moving it
+help: consider mutably borrowing `bar`
    |
 LL |     baz(&mut bar);
    |         ++++

tests/ui/moves/suggest-borrow-for-generic-arg.fixed

@@ -8,15 +8,15 @@ extern crate suggest_borrow_for_generic_arg_aux as aux;
 
 pub fn main() {
     let bar = aux::Bar;
-    aux::foo(&bar); //~ HELP borrow the value
+    aux::foo(&bar); //~ HELP consider borrowing `bar`
     let _baa = bar; //~ ERROR use of moved value
     let mut bar = aux::Bar;
-    aux::qux(&mut bar); //~ HELP borrow the value
+    aux::qux(&mut bar); //~ HELP consider mutably borrowing `bar`
     let _baa = bar; //~ ERROR use of moved value
     let bar = aux::Bar;
-    aux::bat(&bar); //~ HELP borrow the value
+    aux::bat(&bar); //~ HELP consider borrowing `bar`
     let _baa = bar; //~ ERROR use of moved value
     let mut bar = aux::Bar;
-    aux::baz(&mut bar); //~ HELP borrow the value
+    aux::baz(&mut bar); //~ HELP consider mutably borrowing `bar`
     let _baa = bar; //~ ERROR use of moved value
 }

tests/ui/moves/suggest-borrow-for-generic-arg.rs

@@ -8,15 +8,15 @@ extern crate suggest_borrow_for_generic_arg_aux as aux;
 
 pub fn main() {
     let bar = aux::Bar;
-    aux::foo(bar); //~ HELP borrow the value
+    aux::foo(bar); //~ HELP consider borrowing `bar`
     let _baa = bar; //~ ERROR use of moved value
     let mut bar = aux::Bar;
-    aux::qux(bar); //~ HELP borrow the value
+    aux::qux(bar); //~ HELP consider mutably borrowing `bar`
     let _baa = bar; //~ ERROR use of moved value
     let bar = aux::Bar;
-    aux::bat(bar); //~ HELP borrow the value
+    aux::bat(bar); //~ HELP consider borrowing `bar`
     let _baa = bar; //~ ERROR use of moved value
     let mut bar = aux::Bar;
-    aux::baz(bar); //~ HELP borrow the value
+    aux::baz(bar); //~ HELP consider mutably borrowing `bar`
     let _baa = bar; //~ ERROR use of moved value
 }

tests/ui/moves/suggest-borrow-for-generic-arg.stderr

@@ -8,7 +8,7 @@ LL |     aux::foo(bar);
 LL |     let _baa = bar;
    |                ^^^ value used here after move
    |
-help: borrow the value to avoid moving it
+help: consider borrowing `bar`
    |
 LL |     aux::foo(&bar);
    |              +
@@ -23,7 +23,7 @@ LL |     aux::qux(bar);
 LL |     let _baa = bar;
    |                ^^^ value used here after move
    |
-help: borrow the value to avoid moving it
+help: consider mutably borrowing `bar`
    |
 LL |     aux::qux(&mut bar);
    |              ++++
@@ -38,7 +38,7 @@ LL |     aux::bat(bar);
 LL |     let _baa = bar;
    |                ^^^ value used here after move
    |
-help: borrow the value to avoid moving it
+help: consider borrowing `bar`
    |
 LL |     aux::bat(&bar);
    |              +
@@ -53,7 +53,7 @@ LL |     aux::baz(bar);
 LL |     let _baa = bar;
    |                ^^^ value used here after move
    |
-help: borrow the value to avoid moving it
+help: consider mutably borrowing `bar`
    |
 LL |     aux::baz(&mut bar);
    |              ++++