manual_filter: don't eat comments in the and_then suggestion

clippy_lints/src/matches/manual_filter.rs

@@ -1,10 +1,10 @@
-use clippy_utils::as_some_expr;
 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
 use clippy_utils::res::{MaybeDef, MaybeQPath, MaybeResPath};
 use clippy_utils::source::snippet_with_context;
 use clippy_utils::sugg::Sugg;
 use clippy_utils::ty::is_copy;
 use clippy_utils::visitors::contains_unsafe_block;
+use clippy_utils::{as_some_expr, span_contains_comment};
 use rustc_errors::Applicability;
 use rustc_hir::LangItem::OptionNone;
 use rustc_hir::{Arm, Expr, ExprKind, HirId, Pat, PatKind};
@@ -118,7 +118,13 @@ pub(crate) fn check_and_then_method<'tcx>(
             call_span,
             "manual implementation of `Option::filter`",
             |diag| {
-                let mut applicability = Applicability::MachineApplicable;
+                // A comment inside the replaced `and_then` closure (for example, one explaining the
+                // predicate) would be dropped by the rewrite, so don't auto-apply the fix then (#17376).
+                let mut applicability = if span_contains_comment(cx, call_span) {
+                    Applicability::MaybeIncorrect
+                } else {
+                    Applicability::MachineApplicable
+                };
 
                 let mut cond_snip =
                     Sugg::hir_with_context(cx, some_expr.expr, expr_span_ctxt, "..", &mut applicability);

tests/ui/manual_filter_unfixable.rs

@@ -0,0 +1,15 @@
+//@no-rustfix: the suggestion drops the closure's comment, so it is not machine-applicable
+
+#![warn(clippy::manual_filter)]
+
+fn issue17376(opt: Option<u32>) {
+    // Rewriting to `filter` would drop the comment below, so the suggestion must not be
+    // machine-applicable here. Otherwise `clippy --fix` would silently eat the comment (#17376).
+    opt.and_then(|x| {
+        //~^ manual_filter
+        // keep this explanation
+        if x < 10 { Some(x) } else { None }
+    });
+}
+
+fn main() {}

tests/ui/manual_filter_unfixable.stderr

@@ -0,0 +1,16 @@
+error: manual implementation of `Option::filter`
+  --> tests/ui/manual_filter_unfixable.rs:8:9
+   |
+LL |       opt.and_then(|x| {
+   |  _________^
+LL | |
+LL | |         // keep this explanation
+LL | |         if x < 10 { Some(x) } else { None }
+LL | |     });
+   | |______^ help: try: `filter(|&x| x < 10)`
+   |
+   = note: `-D clippy::manual-filter` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::manual_filter)]`
+
+error: aborting due to 1 previous error
+