Explain how to mutate a HashMap/BTreeMap with more nuance

Author: compiler-errors

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -575,7 +575,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                         // ---------- place
                         self.err.multipart_suggestions(
                             format!(
-                                "to modify a `{}`, use `.get_mut()`, `.insert()` or the entry API",
+                                "use `.insert()` to insert a value into a `{}`, `.get_mut()` to modify it, or the entry API for more flexibility",
                                 self.ty,
                             ),
                             vec![

tests/ui/borrowck/index-mut-help.stderr

@@ -14,7 +14,7 @@ LL |     map["peter"] = "0".to_string();
    |     ^^^^^^^^^^^^ cannot assign
    |
    = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `HashMap<&str, String>`
-help: to modify a `HashMap<&str, String>`, use `.get_mut()`, `.insert()` or the entry API
+help: use `.insert()` to insert a value into a `HashMap<&str, String>`, `.get_mut()` to modify it, or the entry API for more flexibility
    |
 LL |     map.insert("peter", "0".to_string());
    |        ~~~~~~~~       ~                +

tests/ui/btreemap/btreemap-index-mut-2.stderr

@@ -5,7 +5,7 @@ LL |         map[&0] = 1;
    |         ^^^^^^^^^^^ cannot assign
    |
    = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `BTreeMap<u32, u32>`
-help: to modify a `BTreeMap<u32, u32>`, use `.get_mut()`, `.insert()` or the entry API
+help: use `.insert()` to insert a value into a `BTreeMap<u32, u32>`, `.get_mut()` to modify it, or the entry API for more flexibility
    |
 LL |         map.insert(&0, 1);
    |            ~~~~~~~~  ~  +

tests/ui/btreemap/btreemap-index-mut.stderr

@@ -5,7 +5,7 @@ LL |     map[&0] = 1;
    |     ^^^^^^^^^^^ cannot assign
    |
    = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `BTreeMap<u32, u32>`
-help: to modify a `BTreeMap<u32, u32>`, use `.get_mut()`, `.insert()` or the entry API
+help: use `.insert()` to insert a value into a `BTreeMap<u32, u32>`, `.get_mut()` to modify it, or the entry API for more flexibility
    |
 LL |     map.insert(&0, 1);
    |        ~~~~~~~~  ~  +

tests/ui/hashmap/hashmap-index-mut.stderr

@@ -5,7 +5,7 @@ LL |     map[&0] = 1;
    |     ^^^^^^^^^^^ cannot assign
    |
    = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `HashMap<u32, u32>`
-help: to modify a `HashMap<u32, u32>`, use `.get_mut()`, `.insert()` or the entry API
+help: use `.insert()` to insert a value into a `HashMap<u32, u32>`, `.get_mut()` to modify it, or the entry API for more flexibility
    |
 LL |     map.insert(&0, 1);
    |        ~~~~~~~~  ~  +