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.

Author: samueltardieu

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(_, _)

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;
+    }
+}