extend while_let_loop to loop { let else } (#15701)

now lints on
```rs
let mut x = [1,2,3].into_iter();
loop {
   let Some(x) = x.next() else { break };
   dbg!(x);
}
```
```
changelog: [`while_let_loop`]: extend to lint on `let else`
```

Author: dswij

clippy_lints/src/loops/mod.rs

@@ -861,6 +861,7 @@ impl<'tcx> LateLintPass<'tcx> for Loops {
         // check for `loop { if let {} else break }` that could be `while let`
         // (also matches an explicit "match" instead of "if let")
         // (even if the "match" or "if let" is used for declaration)
+        // (also matches on `let {} else break`)
         if let ExprKind::Loop(block, label, LoopSource::Loop, _) = expr.kind {
             // also check for empty `loop {}` statements, skipping those in #[panic_handler]
             empty_loop::check(cx, expr, block);

clippy_lints/src/loops/while_let_loop.rs

@@ -10,19 +10,19 @@ use rustc_hir::{Block, Expr, ExprKind, LetStmt, MatchSource, Pat, PatKind, Path,
 use rustc_lint::LateContext;
 
 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, loop_block: &'tcx Block<'_>) {
-    let (init, let_info) = match (loop_block.stmts, loop_block.expr) {
+    let (init, let_info, els) = match (loop_block.stmts, loop_block.expr) {
         ([stmt, ..], _) => match stmt.kind {
             StmtKind::Let(LetStmt {
                 init: Some(e),
-                els: None,
+                els,
                 pat,
                 ty,
                 ..
-            }) => (*e, Some((*pat, *ty))),
-            StmtKind::Semi(e) | StmtKind::Expr(e) => (e, None),
+            }) => (*e, Some((*pat, *ty)), *els),
+            StmtKind::Semi(e) | StmtKind::Expr(e) => (e, None, None),
             _ => return,
         },
-        ([], Some(e)) => (e, None),
+        ([], Some(e)) => (e, None, None),
         _ => return,
     };
     let has_trailing_exprs = loop_block.stmts.len() + usize::from(loop_block.expr.is_some()) > 1;
@@ -38,14 +38,26 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, loop_blo
             if_let.let_expr,
             has_trailing_exprs,
             let_info,
-            if_let.if_then,
+            Some(if_let.if_then),
         );
+    } else if els.and_then(|x| x.expr).is_some_and(is_simple_break_expr)
+        && let Some((pat, _)) = let_info
+    {
+        could_be_while_let(cx, expr, pat, init, has_trailing_exprs, let_info, None);
     } else if let ExprKind::Match(scrutinee, [arm1, arm2], MatchSource::Normal) = init.kind
         && arm1.guard.is_none()
         && arm2.guard.is_none()
         && is_simple_break_expr(arm2.body)
     {
-        could_be_while_let(cx, expr, arm1.pat, scrutinee, has_trailing_exprs, let_info, arm1.body);
+        could_be_while_let(
+            cx,
+            expr,
+            arm1.pat,
+            scrutinee,
+            has_trailing_exprs,
+            let_info,
+            Some(arm1.body),
+        );
     }
 }
 
@@ -70,7 +82,7 @@ fn could_be_while_let<'tcx>(
     let_expr: &'tcx Expr<'_>,
     has_trailing_exprs: bool,
     let_info: Option<(&Pat<'_>, Option<&Ty<'_>>)>,
-    inner_expr: &Expr<'_>,
+    inner_expr: Option<&Expr<'_>>,
 ) {
     if has_trailing_exprs
         && (needs_ordered_drop(cx, cx.typeck_results().expr_ty(let_expr))
@@ -85,7 +97,7 @@ fn could_be_while_let<'tcx>(
     // 1) it was ugly with big bodies;
     // 2) it was not indented properly;
     // 3) it wasn’t very smart (see #675).
-    let inner_content = if let Some((pat, ty)) = let_info
+    let inner_content = if let Some(((pat, ty), inner_expr)) = let_info.zip(inner_expr)
         // Prevent trivial reassignments such as `let x = x;` or `let _ = …;`, but
         // keep them if the type has been explicitly specified.
         && (!is_trivial_assignment(pat, peel_blocks(inner_expr)) || ty.is_some())

tests/ui/infinite_loops.rs

@@ -1,7 +1,7 @@
 //@no-rustfix: multiple suggestions add `-> !` to the same fn
 //@aux-build:proc_macros.rs
 
-#![allow(clippy::never_loop)]
+#![allow(clippy::never_loop, clippy::while_let_loop)]
 #![warn(clippy::infinite_loop)]
 
 extern crate proc_macros;

tests/ui/while_let_loop.rs

@@ -22,6 +22,19 @@ fn main() {
         break;
     }
 
+    loop {
+        //~^ while_let_loop
+        let Some(_x) = y else { break };
+    }
+
+    loop {
+        // no error, else branch does something other than break
+        let Some(_x) = y else {
+            let _z = 1;
+            break;
+        };
+    }
+
     loop {
         //~^ while_let_loop
 

tests/ui/while_let_loop.stderr

@@ -17,6 +17,15 @@ error: this loop could be written as a `while let` loop
    |
 LL | /     loop {
 LL | |
+LL | |         let Some(_x) = y else { break };
+LL | |     }
+   | |_____^ help: try: `while let Some(_x) = y { .. }`
+
+error: this loop could be written as a `while let` loop
+  --> tests/ui/while_let_loop.rs:38:5
+   |
+LL | /     loop {
+LL | |
 LL | |
 LL | |         match y {
 ...  |
@@ -25,7 +34,7 @@ LL | |     }
    | |_____^ help: try: `while let Some(_x) = y { .. }`
 
 error: this loop could be written as a `while let` loop
-  --> tests/ui/while_let_loop.rs:34:5
+  --> tests/ui/while_let_loop.rs:47:5
    |
 LL | /     loop {
 LL | |
@@ -37,7 +46,7 @@ LL | |     }
    | |_____^ help: try: `while let Some(x) = y { .. }`
 
 error: this loop could be written as a `while let` loop
-  --> tests/ui/while_let_loop.rs:45:5
+  --> tests/ui/while_let_loop.rs:58:5
    |
 LL | /     loop {
 LL | |
@@ -48,7 +57,7 @@ LL | |     }
    | |_____^ help: try: `while let Some(x) = y { .. }`
 
 error: this loop could be written as a `while let` loop
-  --> tests/ui/while_let_loop.rs:77:5
+  --> tests/ui/while_let_loop.rs:90:5
    |
 LL | /     loop {
 LL | |
@@ -68,7 +77,7 @@ LL +     }
    |
 
 error: this loop could be written as a `while let` loop
-  --> tests/ui/while_let_loop.rs:167:9
+  --> tests/ui/while_let_loop.rs:180:9
    |
 LL | /         loop {
 LL | |
@@ -88,7 +97,7 @@ LL +         }
    |
 
 error: this loop could be written as a `while let` loop
-  --> tests/ui/while_let_loop.rs:182:5
+  --> tests/ui/while_let_loop.rs:195:5
    |
 LL | /     loop {
 LL | |
@@ -107,7 +116,7 @@ LL +     }
    |
 
 error: this loop could be written as a `while let` loop
-  --> tests/ui/while_let_loop.rs:194:5
+  --> tests/ui/while_let_loop.rs:207:5
    |
 LL | /     loop {
 LL | |
@@ -126,7 +135,7 @@ LL +     }
    |
 
 error: this loop could be written as a `while let` loop
-  --> tests/ui/while_let_loop.rs:206:5
+  --> tests/ui/while_let_loop.rs:219:5
    |
 LL | /     loop {
 LL | |
@@ -137,7 +146,7 @@ LL | |     }
    | |_____^ help: try: `while let Some(x) = Some(3) { .. }`
 
 error: this loop could be written as a `while let` loop
-  --> tests/ui/while_let_loop.rs:218:5
+  --> tests/ui/while_let_loop.rs:231:5
    |
 LL | /     loop {
 LL | |
@@ -156,7 +165,7 @@ LL +     }
    |
 
 error: this loop could be written as a `while let` loop
-  --> tests/ui/while_let_loop.rs:230:5
+  --> tests/ui/while_let_loop.rs:243:5
    |
 LL | /     loop {
 LL | |
@@ -177,5 +186,5 @@ LL +         ..
 LL +     }
    |
 
-error: aborting due to 11 previous errors
+error: aborting due to 12 previous errors