Fix if_then_some_else_none FP when the then block contains await codes

Closes #16176

Author: relaxcn

clippy_lints/src/if_then_some_else_none.rs

@@ -1,12 +1,15 @@
+use std::ops::ControlFlow;
+
 use clippy_config::Conf;
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::eager_or_lazy::switch_to_eager_eval;
 use clippy_utils::msrvs::{self, Msrv};
 use clippy_utils::source::{snippet_with_applicability, snippet_with_context, walk_span_to_context};
 use clippy_utils::sugg::Sugg;
+use clippy_utils::visitors::for_each_expr_without_closures;
 use clippy_utils::{
-    as_some_expr, contains_return, expr_adjustment_requires_coercion, higher, is_else_clause, is_in_const_context,
-    is_none_expr, peel_blocks, sym,
+    as_some_expr, contains_return, desugar_await, expr_adjustment_requires_coercion, higher, is_else_clause,
+    is_in_const_context, is_none_expr, peel_blocks, sym,
 };
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind};
@@ -77,7 +80,18 @@ impl<'tcx> LateLintPass<'tcx> for IfThenSomeElseNone {
             && !is_in_const_context(cx)
             && self.msrv.meets(cx, msrvs::BOOL_THEN)
             && !contains_return(then_block.stmts)
-            && then_block.expr.is_none_or(|expr| !contains_return(expr))
+            && then_block.expr.is_none_or(|expr| {
+                !contains_return(expr)
+                    // `bool::then` doesn't work with async code
+                    && for_each_expr_without_closures(expr, |e| {
+                        if desugar_await(e).is_some() {
+                            ControlFlow::Break(())
+                        } else {
+                            ControlFlow::Continue(())
+                        }
+                    })
+                    .is_none()
+            })
         {
             let method_name = if switch_to_eager_eval(cx, expr) && self.msrv.meets(cx, msrvs::BOOL_THEN_SOME) {
                 sym::then_some

tests/ui/if_then_some_else_none.fixed

@@ -218,3 +218,13 @@ mod issue15770 {
         Ok(())
     }
 }
+
+mod issue16176 {
+    pub async fn foo() -> u32 {
+        todo!()
+    }
+
+    pub async fn bar(cond: bool) -> Option<u32> {
+        if cond { Some(foo().await) } else { None } // OK
+    }
+}

tests/ui/if_then_some_else_none.rs

@@ -274,3 +274,13 @@ mod issue15770 {
         Ok(())
     }
 }
+
+mod issue16176 {
+    pub async fn foo() -> u32 {
+        todo!()
+    }
+
+    pub async fn bar(cond: bool) -> Option<u32> {
+        if cond { Some(foo().await) } else { None } // OK
+    }
+}