fix(map_entry): don't autofix when {e.insert(_); None } would be required

Author: ada4a

clippy_lints/src/entry.rs

@@ -682,6 +682,8 @@ impl<'tcx> InsertSearchResults<'tcx> {
                 } else {
                     write!(res, "{{ e.insert({value_str}); None }}")
                 };
+                // This might leave `None`'s type ambiguous, so reduce applicability
+                *app = Applicability::MaybeIncorrect;
             }),
             "Vacant(e)",
         )

tests/ui/entry_unfixable.rs

@@ -1,3 +1,4 @@
+//@no-rustfix
 #![allow(clippy::needless_pass_by_value, clippy::collapsible_if)]
 #![warn(clippy::map_entry)]
 
@@ -90,4 +91,11 @@ mod issue13306 {
     }
 }
 
+fn issue15307<K: Eq + Hash, V>(mut m: HashMap<K, V>, k: K, v: V) {
+    if !m.contains_key(&k) {
+        //~^ map_entry
+        assert!(m.insert(k, v).is_none());
+    }
+}
+
 fn main() {}

tests/ui/entry_unfixable.stderr

@@ -1,5 +1,5 @@
 error: usage of `contains_key` followed by `insert` on a `HashMap`
-  --> tests/ui/entry_unfixable.rs:46:13
+  --> tests/ui/entry_unfixable.rs:47:13
    |
 LL | /             if self.globals.contains_key(&name) {
 LL | |
@@ -15,7 +15,7 @@ LL | |             }
    = help: to override `-D warnings` add `#[allow(clippy::map_entry)]`
 
 error: usage of `contains_key` followed by `insert` on a `HashMap`
-  --> tests/ui/entry_unfixable.rs:61:5
+  --> tests/ui/entry_unfixable.rs:62:5
    |
 LL | /     if hm.contains_key(&key) {
 LL | |
@@ -29,7 +29,7 @@ LL | |     }
    = help: consider using the `Entry` API: https://doc.rust-lang.org/std/collections/struct.HashMap.html#entry-api
 
 error: usage of `contains_key` followed by `insert` on a `HashMap`
-  --> tests/ui/entry_unfixable.rs:80:13
+  --> tests/ui/entry_unfixable.rs:81:13
    |
 LL | /             if !self.values.contains_key(&name) {
 LL | |
@@ -42,5 +42,22 @@ LL | |             }
    |
    = help: consider using the `Entry` API: https://doc.rust-lang.org/std/collections/struct.HashMap.html#entry-api
 
-error: aborting due to 3 previous errors
+error: usage of `contains_key` followed by `insert` on a `HashMap`
+  --> tests/ui/entry_unfixable.rs:95:5
+   |
+LL | /     if !m.contains_key(&k) {
+LL | |
+LL | |         assert!(m.insert(k, v).is_none());
+LL | |     }
+   | |_____^
+   |
+help: try
+   |
+LL ~     if let std::collections::hash_map::Entry::Vacant(e) = m.entry(k) {
+LL +
+LL +         assert!({ e.insert(v); None }.is_none());
+LL +     }
+   |
+
+error: aborting due to 4 previous errors