Fix for_kv_map FN when using iter and iter_mut (#16830)

Closes rust-lang/rust-clippy#16822

changelog: [`for_kv_map`] fix FN when using `iter` and `iter_mut`

clippy_lints/src/loops/for_kv_map.rs

@@ -23,7 +23,20 @@ pub(super) fn check<'tcx>(
         && pat.len() == 2
     {
         let arg_span = arg.span;
-        let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
+        let (arg, arg_ty) = match arg.kind {
+            // `for x in &expr` or `for x in &mut expr`
+            ExprKind::AddrOf(BorrowKind::Ref, _, expr) => (expr, cx.typeck_results().expr_ty(arg)),
+            // `for x in receiver.iter()` or `for x in receiver.iter_mut()`
+            ExprKind::MethodCall(path, receiver, [], ..)
+                if path.ident.name == sym::iter || path.ident.name == sym::iter_mut =>
+            {
+                // Use `expr_ty_adjusted` because `.iter()` / `.iter_mut()` may introduce auto deferences
+                (receiver, cx.typeck_results().expr_ty_adjusted(receiver))
+            },
+            _ => (arg, cx.typeck_results().expr_ty(arg)),
+        };
+
+        let (new_pat_span, kind, ty, mutbl) = match *arg_ty.kind() {
             ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
                 (key, _) if pat_is_wild(cx, key, body) => (pat[1].span, "value", ty, mutbl),
                 (_, value) if pat_is_wild(cx, value, body) => (pat[0].span, "key", ty, Mutability::Not),
@@ -35,10 +48,6 @@ pub(super) fn check<'tcx>(
             Mutability::Not => "",
             Mutability::Mut => "_mut",
         };
-        let arg = match arg.kind {
-            ExprKind::AddrOf(BorrowKind::Ref, _, expr) => expr,
-            _ => arg,
-        };
 
         if matches!(ty.opt_diag_name(cx), Some(sym::HashMap | sym::BTreeMap))
             && let Some(arg_span) = walk_span_to_context(arg_span, span.ctxt())

tests/ui/for_kv_map.fixed

@@ -86,3 +86,25 @@ fn wrongly_unmangled_macros() {
         let _v = v;
     }
 }
+
+fn issue16822(mut x: HashMap<usize, usize>) {
+    for v in x.values() {
+        //~^ for_kv_map
+        println!("{}", v);
+    }
+
+    for v in x.values_mut() {
+        //~^ for_kv_map
+        *v += 1;
+    }
+
+    for k in x.keys() {
+        //~^ for_kv_map
+        println!("{}", k);
+    }
+
+    for k in x.keys() {
+        //~^ for_kv_map
+        println!("{}", k);
+    }
+}

tests/ui/for_kv_map.rs

@@ -86,3 +86,25 @@ macro_rules! test_map {
         let _v = v;
     }
 }
+
+fn issue16822(mut x: HashMap<usize, usize>) {
+    for (_, v) in x.iter() {
+        //~^ for_kv_map
+        println!("{}", v);
+    }
+
+    for (_, v) in x.iter_mut() {
+        //~^ for_kv_map
+        *v += 1;
+    }
+
+    for (k, _) in x.iter() {
+        //~^ for_kv_map
+        println!("{}", k);
+    }
+
+    for (k, _) in x.iter_mut() {
+        //~^ for_kv_map
+        println!("{}", k);
+    }
+}

tests/ui/for_kv_map.stderr

@@ -84,5 +84,53 @@ LL -     for (_, v) in test_map!(wrapped) {
 LL +     for v in test_map!(wrapped).values() {
    |
 
-error: aborting due to 7 previous errors
+error: you seem to want to iterate on a map's values
+  --> tests/ui/for_kv_map.rs:91:19
+   |
+LL |     for (_, v) in x.iter() {
+   |                   ^^^^^^^^
+   |
+help: use the corresponding method
+   |
+LL -     for (_, v) in x.iter() {
+LL +     for v in x.values() {
+   |
+
+error: you seem to want to iterate on a map's values
+  --> tests/ui/for_kv_map.rs:96:19
+   |
+LL |     for (_, v) in x.iter_mut() {
+   |                   ^^^^^^^^^^^^
+   |
+help: use the corresponding method
+   |
+LL -     for (_, v) in x.iter_mut() {
+LL +     for v in x.values_mut() {
+   |
+
+error: you seem to want to iterate on a map's keys
+  --> tests/ui/for_kv_map.rs:101:19
+   |
+LL |     for (k, _) in x.iter() {
+   |                   ^^^^^^^^
+   |
+help: use the corresponding method
+   |
+LL -     for (k, _) in x.iter() {
+LL +     for k in x.keys() {
+   |
+
+error: you seem to want to iterate on a map's keys
+  --> tests/ui/for_kv_map.rs:106:19
+   |
+LL |     for (k, _) in x.iter_mut() {
+   |                   ^^^^^^^^^^^^
+   |
+help: use the corresponding method
+   |
+LL -     for (k, _) in x.iter_mut() {
+LL +     for k in x.keys() {
+   |
+
+error: aborting due to 11 previous errors