From d94a9febaed8554e1e9ebc9c007e0097f8f43545 Mon Sep 17 00:00:00 2001
From: Samuel Tardieu <sam@rfc1149.net>
Date: Sun, 14 Sep 2025 09:02:15 +0200
Subject: [PATCH] Consider labels of inline asm as conditionally executed

Since an `asm!()` statement is mostly unknown, as we do not know what it
does, consider all labels' `break` as being conditionally executed only.
---
 clippy_lints/src/loops/never_loop.rs | 19 ++++++-
 tests/ui/never_loop.rs               | 41 ++++++++++++---
 tests/ui/never_loop.stderr           | 77 ++++++++++++++++------------
 3 files changed, 94 insertions(+), 43 deletions(-)

diff --git a/clippy_lints/src/loops/never_loop.rs b/clippy_lints/src/loops/never_loop.rs
index 544c3c34d029..d01ce22c99a5 100644
--- a/clippy_lints/src/loops/never_loop.rs
+++ b/clippy_lints/src/loops/never_loop.rs
@@ -7,7 +7,7 @@ use clippy_utils::source::snippet;
 use clippy_utils::visitors::{Descend, for_each_expr_without_closures};
 use rustc_errors::Applicability;
 use rustc_hir::{
-    Block, Destination, Expr, ExprKind, HirId, InlineAsmOperand, Node, Pat, Stmt, StmtKind, StructTailExpr,
+    Block, Destination, Expr, ExprKind, HirId, InlineAsm, InlineAsmOperand, Node, Pat, Stmt, StmtKind, StructTailExpr,
 };
 use rustc_lint::LateContext;
 use rustc_span::{BytePos, Span, sym};
@@ -75,12 +75,19 @@ pub(super) fn check<'tcx>(
 fn contains_any_break_or_continue(block: &Block<'_>) -> bool {
     for_each_expr_without_closures(block, |e| match e.kind {
         ExprKind::Break(..) | ExprKind::Continue(..) => ControlFlow::Break(()),
+        ExprKind::InlineAsm(asm) if contains_label(asm) => ControlFlow::Break(()),
         ExprKind::Loop(..) => ControlFlow::Continue(Descend::No),
         _ => ControlFlow::Continue(Descend::Yes),
     })
     .is_some()
 }
 
+fn contains_label(asm: &InlineAsm<'_>) -> bool {
+    asm.operands
+        .iter()
+        .any(|(op, _span)| matches!(op, InlineAsmOperand::Label { .. }))
+}
+
 /// The `never_loop` analysis keeps track of three things:
 ///
 /// * Has any (reachable) code path hit a `continue` of the main loop?
@@ -378,7 +385,15 @@ fn never_loop_expr<'tcx>(
             InlineAsmOperand::Const { .. } | InlineAsmOperand::SymFn { .. } | InlineAsmOperand::SymStatic { .. } => {
                 NeverLoopResult::Normal
             },
-            InlineAsmOperand::Label { block } => never_loop_block(cx, block, local_labels, main_loop_id),
+            InlineAsmOperand::Label { block } =>
+            // We do not know whether the label will be executed or not, so `Diverging` must be
+            // downgraded to `Normal`.
+            {
+                match never_loop_block(cx, block, local_labels, main_loop_id) {
+                    NeverLoopResult::Diverging { .. } => NeverLoopResult::Normal,
+                    result => result,
+                }
+            },
         })),
         ExprKind::OffsetOf(_, _)
         | ExprKind::Yield(_, _)
diff --git a/tests/ui/never_loop.rs b/tests/ui/never_loop.rs
index 01db64a446c0..5f71f9f1729f 100644
--- a/tests/ui/never_loop.rs
+++ b/tests/ui/never_loop.rs
@@ -1,12 +1,9 @@
 #![feature(try_blocks)]
-#![allow(
-    clippy::eq_op,
-    clippy::single_match,
-    unused_assignments,
-    unused_variables,
-    clippy::while_immutable_condition
-)]
+#![expect(clippy::eq_op, clippy::single_match, clippy::while_immutable_condition)]
 //@no-rustfix
+
+use std::arch::asm;
+
 fn test1() {
     let mut x = 0;
     loop {
@@ -522,3 +519,33 @@ fn issue15350() {
         }
     }
 }
+
+fn issue15673() {
+    loop {
+        unsafe {
+            // No lint since we don't analyze the inside of the asm
+            asm! {
+                "/* {} */",
+                label {
+                    break;
+                }
+            }
+        }
+    }
+
+    //~v never_loop
+    loop {
+        // We don't check the applicability in tests, but this should
+        // be `Applicability::MaybeIncorrect` because of the `break`
+        // in the `asm!()` labels.
+        unsafe {
+            asm! {
+                "/* {} */",
+                label {
+                    break;
+                }
+            }
+        }
+        return;
+    }
+}
diff --git a/tests/ui/never_loop.stderr b/tests/ui/never_loop.stderr
index 4fda06cff4ab..7a33a5a5528a 100644
--- a/tests/ui/never_loop.stderr
+++ b/tests/ui/never_loop.stderr
@@ -1,5 +1,5 @@
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:12:5
+  --> tests/ui/never_loop.rs:9:5
    |
 LL | /     loop {
 ...  |
@@ -10,7 +10,7 @@ LL | |     }
    = note: `#[deny(clippy::never_loop)]` on by default
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:36:5
+  --> tests/ui/never_loop.rs:33:5
    |
 LL | /     loop {
 ...  |
@@ -19,7 +19,7 @@ LL | |     }
    | |_____^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:58:5
+  --> tests/ui/never_loop.rs:55:5
    |
 LL | /     loop {
 ...  |
@@ -28,7 +28,7 @@ LL | |     }
    | |_____^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:62:9
+  --> tests/ui/never_loop.rs:59:9
    |
 LL | /         while i == 0 {
 ...  |
@@ -36,7 +36,7 @@ LL | |         }
    | |_________^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:76:9
+  --> tests/ui/never_loop.rs:73:9
    |
 LL | /         loop {
 ...  |
@@ -45,7 +45,7 @@ LL | |         }
    | |_________^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:114:5
+  --> tests/ui/never_loop.rs:111:5
    |
 LL | /     while let Some(y) = x {
 ...  |
@@ -53,7 +53,7 @@ LL | |     }
    | |_____^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:123:5
+  --> tests/ui/never_loop.rs:120:5
    |
 LL | /     for x in 0..10 {
 ...  |
@@ -67,7 +67,7 @@ LL +     if let Some(x) = (0..10).next() {
    |
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:173:5
+  --> tests/ui/never_loop.rs:170:5
    |
 LL | /     'outer: while a {
 ...  |
@@ -76,7 +76,7 @@ LL | |     }
    | |_____^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:190:9
+  --> tests/ui/never_loop.rs:187:9
    |
 LL | /         while false {
 LL | |
@@ -86,7 +86,7 @@ LL | |         }
    | |_________^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:243:13
+  --> tests/ui/never_loop.rs:240:13
    |
 LL |       let _ = loop {
    |  _____________^
@@ -99,7 +99,7 @@ LL | |     };
    | |_____^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:266:5
+  --> tests/ui/never_loop.rs:263:5
    |
 LL | /     'a: loop {
 LL | |
@@ -110,7 +110,7 @@ LL | |     }
    | |_____^
 
 error: sub-expression diverges
-  --> tests/ui/never_loop.rs:271:17
+  --> tests/ui/never_loop.rs:268:17
    |
 LL |                 break 'a;
    |                 ^^^^^^^^
@@ -119,7 +119,7 @@ LL |                 break 'a;
    = help: to override `-D warnings` add `#[allow(clippy::diverging_sub_expression)]`
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:303:13
+  --> tests/ui/never_loop.rs:300:13
    |
 LL | /             for _ in 0..20 {
 LL | |
@@ -135,7 +135,7 @@ LL +             if let Some(_) = (0..20).next() {
    |
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:388:13
+  --> tests/ui/never_loop.rs:385:13
    |
 LL | /             'c: loop {
 LL | |
@@ -145,7 +145,7 @@ LL | |             }
    | |_____________^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:400:5
+  --> tests/ui/never_loop.rs:397:5
    |
 LL | /     loop {
 LL | |
@@ -155,7 +155,7 @@ LL | |     }
    | |_____^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:405:5
+  --> tests/ui/never_loop.rs:402:5
    |
 LL | /     loop {
 LL | |
@@ -165,7 +165,7 @@ LL | |     }
    | |_____^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:426:5
+  --> tests/ui/never_loop.rs:423:5
    |
 LL | /     for v in 0..10 {
 LL | |
@@ -183,7 +183,7 @@ LL ~
    |
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:434:5
+  --> tests/ui/never_loop.rs:431:5
    |
 LL | /     'outer: for v in 0..10 {
 LL | |
@@ -194,7 +194,7 @@ LL | |     }
    | |_____^
    |
 help: this code is unreachable. Consider moving the reachable parts out
-  --> tests/ui/never_loop.rs:436:9
+  --> tests/ui/never_loop.rs:433:9
    |
 LL | /         loop {
 LL | |
@@ -202,7 +202,7 @@ LL | |             break 'outer;
 LL | |         }
    | |_________^
 help: this code is unreachable. Consider moving the reachable parts out
-  --> tests/ui/never_loop.rs:440:9
+  --> tests/ui/never_loop.rs:437:9
    |
 LL |         return;
    |         ^^^^^^^
@@ -213,7 +213,7 @@ LL +     if let Some(v) = (0..10).next() {
    |
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:436:9
+  --> tests/ui/never_loop.rs:433:9
    |
 LL | /         loop {
 LL | |
@@ -222,7 +222,7 @@ LL | |         }
    | |_________^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:443:5
+  --> tests/ui/never_loop.rs:440:5
    |
 LL | /     for v in 0..10 {
 LL | |
@@ -239,7 +239,7 @@ LL +     if let Some(v) = (0..10).next() {
    |
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:445:9
+  --> tests/ui/never_loop.rs:442:9
    |
 LL | /         'inner: loop {
 LL | |
@@ -248,7 +248,7 @@ LL | |         }
    | |_________^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:471:5
+  --> tests/ui/never_loop.rs:468:5
    |
 LL | /     'a: for _ in 0..1 {
 LL | |
@@ -264,7 +264,7 @@ LL ~
    |
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:477:5
+  --> tests/ui/never_loop.rs:474:5
    |
 LL | /     'a: for i in 0..1 {
 LL | |
@@ -288,7 +288,7 @@ LL ~
    |
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:492:5
+  --> tests/ui/never_loop.rs:489:5
    |
 LL | /     for v in 0..10 {
 LL | |
@@ -311,7 +311,7 @@ LL ~
    |
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:503:5
+  --> tests/ui/never_loop.rs:500:5
    |
 LL | /     'bar: for _ in 0..100 {
 LL | |
@@ -321,7 +321,7 @@ LL | |     }
    | |_____^
    |
 help: this code is unreachable. Consider moving the reachable parts out
-  --> tests/ui/never_loop.rs:505:9
+  --> tests/ui/never_loop.rs:502:9
    |
 LL | /         loop {
 LL | |
@@ -336,7 +336,7 @@ LL +     if let Some(_) = (0..100).next() {
    |
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:505:9
+  --> tests/ui/never_loop.rs:502:9
    |
 LL | /         loop {
 LL | |
@@ -346,7 +346,7 @@ LL | |         }
    | |_________^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:512:5
+  --> tests/ui/never_loop.rs:509:5
    |
 LL | /     'foo: for _ in 0..100 {
 LL | |
@@ -356,7 +356,7 @@ LL | |     }
    | |_____^
    |
 help: this code is unreachable. Consider moving the reachable parts out
-  --> tests/ui/never_loop.rs:514:9
+  --> tests/ui/never_loop.rs:511:9
    |
 LL | /         loop {
 LL | |
@@ -372,7 +372,7 @@ LL +     if let Some(_) = (0..100).next() {
    |
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:514:9
+  --> tests/ui/never_loop.rs:511:9
    |
 LL | /         loop {
 LL | |
@@ -383,7 +383,7 @@ LL | |         }
    | |_________^
 
 error: this loop never actually loops
-  --> tests/ui/never_loop.rs:517:13
+  --> tests/ui/never_loop.rs:514:13
    |
 LL | /             loop {
 LL | |
@@ -392,5 +392,14 @@ LL | |                 break 'foo;
 LL | |             }
    | |_____________^
 
-error: aborting due to 29 previous errors
+error: this loop never actually loops
+  --> tests/ui/never_loop.rs:537:5
+   |
+LL | /     loop {
+...  |
+LL | |         return;
+LL | |     }
+   | |_____^
+
+error: aborting due to 30 previous errors