changelog: Fix [manual_flatten] with nested Some or Ok pattern

Author: a-yossy

clippy_lints/src/loops/manual_flatten.rs

@@ -28,7 +28,7 @@ pub(super) fn check<'tcx>(
         && let PatKind::Binding(_, pat_hir_id, _, _) = pat.kind
         && path_to_local_id(let_expr, pat_hir_id)
         // Ensure the `if let` statement is for the `Some` variant of `Option` or the `Ok` variant of `Result`
-        && let PatKind::TupleStruct(ref qpath, _, _) = let_pat.kind
+        && let PatKind::TupleStruct(ref qpath, pats, _) = let_pat.kind
         && let Res::Def(DefKind::Ctor(..), ctor_id) = cx.qpath_res(qpath, let_pat.hir_id)
         && let Some(variant_id) = cx.tcx.opt_parent(ctor_id)
         && let some_ctor = cx.tcx.lang_items().option_some_variant() == Some(variant_id)
@@ -39,9 +39,13 @@ pub(super) fn check<'tcx>(
         && msrv.meets(cx, msrvs::ITER_FLATTEN)
     {
         let if_let_type = if some_ctor { "Some" } else { "Ok" };
+        let has_nested_tuple_struct = contains_nested_tuple_struct(pats);
         // Prepare the error message
-        let msg =
-            format!("unnecessary `if let` since only the `{if_let_type}` variant of the iterator element is used");
+        let msg = if has_nested_tuple_struct {
+            "manual flattening detected".to_string()
+        } else {
+            format!("unnecessary `if let` since only the `{if_let_type}` variant of the iterator element is used")
+        };
 
         // Prepare the help message
         let mut applicability = Applicability::MaybeIncorrect;
@@ -60,9 +64,15 @@ pub(super) fn check<'tcx>(
         // case, it will be shown in the extra `help` message at the end, which is why the first
         // `help_msg` needs to refer to the correct relative position of the suggestion.
         let help_msg = if sugg.contains('\n') {
-            "remove the `if let` statement in the for loop and then..."
+            if has_nested_tuple_struct {
+                format!("remove the outer `{if_let_type}` variant in the for loop and then...")
+            } else {
+                "remove the `if let` statement in the for loop and then...".to_string()
+            }
+        } else if has_nested_tuple_struct {
+            format!("...and remove the outer `{if_let_type}` variant in the for loop")
         } else {
-            "...and remove the `if let` statement in the for loop"
+            "...and remove the `if let` statement in the for loop".to_string()
         };
 
         span_lint_and_then(cx, MANUAL_FLATTEN, span, msg, |diag| {
@@ -71,3 +81,19 @@ pub(super) fn check<'tcx>(
         });
     }
 }
+
+fn contains_nested_tuple_struct(pats: &[Pat<'_>]) -> bool {
+    for pat in pats {
+        match pat.kind {
+            PatKind::TupleStruct(_, _, _) => {
+                return true;
+            },
+            PatKind::Tuple(pats, _) => {
+                return contains_nested_tuple_struct(pats);
+            },
+            _ => {},
+        }
+    }
+
+    false
+}

tests/ui/manual_flatten.rs

@@ -123,6 +123,16 @@ fn main() {
         println!("{}", n);
     }
 
+    // Test for loop with nested Some pattern with `if let` expression
+    let z = vec![Some((0, Some(0)))];
+    for n in z {
+        //~^ manual_flatten
+
+        if let Some((_, Some(n))) = n {
+            println!("{}", n);
+        }
+    }
+
     run_unformatted_tests();
 }
 

tests/ui/manual_flatten.stderr

@@ -177,8 +177,30 @@ LL | |             println!("{:?}", n);
 LL | |         }
    | |_________^
 
+error: manual flattening detected
+  --> tests/ui/manual_flatten.rs:128:5
+   |
+LL |       for n in z {
+   |       ^        - help: try: `z.into_iter().flatten()`
+   |  _____|
+   | |
+LL | |
+LL | |
+LL | |         if let Some((_, Some(n))) = n {
+...  |
+LL | |     }
+   | |_____^
+   |
+help: ...and remove the outer `Some` variant in the for loop
+  --> tests/ui/manual_flatten.rs:131:9
+   |
+LL | /         if let Some((_, Some(n))) = n {
+LL | |             println!("{}", n);
+LL | |         }
+   | |_________^
+
 error: unnecessary `if let` since only the `Some` variant of the iterator element is used
-  --> tests/ui/manual_flatten.rs:132:5
+  --> tests/ui/manual_flatten.rs:142:5
    |
 LL | /     for n in vec![
 LL | |
@@ -189,7 +211,7 @@ LL | |     }
    | |_____^
    |
 help: remove the `if let` statement in the for loop and then...
-  --> tests/ui/manual_flatten.rs:139:9
+  --> tests/ui/manual_flatten.rs:149:9
    |
 LL | /         if let Some(n) = n {
 LL | |             println!("{:?}", n);
@@ -203,5 +225,5 @@ LL |         Some(3)
 LL ~     ].iter().flatten() {
    |
 
-error: aborting due to 9 previous errors
+error: aborting due to 10 previous errors