Auto merge of #13149 - jusexton:issue-13123, r=dswij

Fix while_let_on_iterator dropping loop label when applying fix.

Loop label was not persisted when displaying help and was therefore producing broken rust code when applying fixes.

Solution was to store the `ast::Label` when creating a `higher::WhileLet` from an expression and add the label name to the lint suggestion and diagnostics.

---

Fixes: #13123

changelog: [`while_let_on_iterator`]: Fix issue dropping loop label when displaying help and applying fixes.

Author: bors

clippy_lints/src/loops/while_let_on_iterator.rs

@@ -14,7 +14,7 @@ use rustc_span::symbol::sym;
 use rustc_span::Symbol;
 
 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-    if let Some(higher::WhileLet { if_then, let_pat, let_expr, .. }) = higher::WhileLet::hir(expr)
+    if let Some(higher::WhileLet { if_then, let_pat, let_expr, label, .. }) = higher::WhileLet::hir(expr)
         // check for `Some(..)` pattern
         && let PatKind::TupleStruct(ref pat_path, some_pat, _) = let_pat.kind
         && is_res_lang_ctor(cx, cx.qpath_res(pat_path, let_pat.hir_id), LangItem::OptionSome)
@@ -27,6 +27,9 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         && !uses_iter(cx, &iter_expr_struct, if_then)
     {
         let mut applicability = Applicability::MachineApplicable;
+
+        let loop_label = label.map_or(String::new(), |l| format!("{}: ", l.ident.name));
+
         let loop_var = if let Some(some_pat) = some_pat.first() {
             if is_refutable(cx, some_pat) {
                 // Refutable patterns don't work with for loops.
@@ -57,7 +60,7 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
             expr.span.with_hi(let_expr.span.hi()),
             "this loop could be written as a `for` loop",
             "try",
-            format!("for {loop_var} in {iterator}{by_ref}"),
+            format!("{loop_label}for {loop_var} in {iterator}{by_ref}"),
             applicability,
         );
     }

clippy_utils/src/higher.rs

@@ -367,6 +367,7 @@ pub struct WhileLet<'hir> {
     pub let_expr: &'hir Expr<'hir>,
     /// `while let` loop body
     pub if_then: &'hir Expr<'hir>,
+    pub label: Option<ast::Label>,
     /// `while let PAT = EXPR`
     ///        ^^^^^^^^^^^^^^
     pub let_span: Span,
@@ -399,7 +400,7 @@ impl<'hir> WhileLet<'hir> {
                     }),
                 ..
             },
-            _,
+            label,
             LoopSource::While,
             _,
         ) = expr.kind
@@ -408,6 +409,7 @@ impl<'hir> WhileLet<'hir> {
                 let_pat,
                 let_expr,
                 if_then,
+                label,
                 let_span,
             });
         }

tests/ui/while_let_on_iterator.fixed

@@ -456,6 +456,15 @@ fn fn_once_closure() {
     });
 }
 
+fn issue13123() {
+    let mut it = 0..20;
+    'label: for n in it {
+        if n % 25 == 0 {
+            break 'label;
+        }
+    }
+}
+
 fn main() {
     let mut it = 0..20;
     for _ in it {

tests/ui/while_let_on_iterator.rs

@@ -456,6 +456,15 @@ fn fn_once_closure() {
     });
 }
 
+fn issue13123() {
+    let mut it = 0..20;
+    'label: while let Some(n) = it.next() {
+        if n % 25 == 0 {
+            break 'label;
+        }
+    }
+}
+
 fn main() {
     let mut it = 0..20;
     while let Some(..) = it.next() {

tests/ui/while_let_on_iterator.stderr

@@ -160,8 +160,14 @@ LL |         while let Some(x) = it.next() {
 error: this loop could be written as a `for` loop
   --> tests/ui/while_let_on_iterator.rs:461:5
    |
+LL |     'label: while let Some(n) = it.next() {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `'label: for n in it`
+
+error: this loop could be written as a `for` loop
+  --> tests/ui/while_let_on_iterator.rs:470:5
+   |
 LL |     while let Some(..) = it.next() {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for _ in it`
 
-error: aborting due to 27 previous errors
+error: aborting due to 28 previous errors