make sure checked type implements Try trait when linting [question_mark]

clippy_lints/src/question_mark.rs

@@ -4,7 +4,7 @@ use clippy_config::msrvs::Msrv;
 use clippy_config::types::MatchLintBehaviour;
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet_with_applicability;
-use clippy_utils::ty::is_type_diagnostic_item;
+use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
 use clippy_utils::{
     eq_expr_value, higher, in_constant, is_else_clause, is_lint_allowed, is_path_lang_item, is_res_lang_ctor,
     pat_and_expr_can_be_question_mark, path_to_local, path_to_local_id, peel_blocks, peel_blocks_with_stmt,
@@ -109,12 +109,31 @@ fn find_let_else_ret_expression<'hir>(block: &'hir Block<'hir>) -> Option<&'hir
 }
 
 fn check_let_some_else_return_none(cx: &LateContext<'_>, stmt: &Stmt<'_>) {
+    /// Make sure the init expr implements try trait so a valid suggestion could be given.
+    ///
+    /// Because the init expr could have the type of `&Option<T>` which does not implements `Try`.
+    ///
+    /// NB: This conveniently prevents the cause of
+    /// issue [#12412](https://github.com/rust-lang/rust-clippy/issues/12412),
+    /// since accessing an `Option` field from a borrowed struct requires borrow, such as
+    /// `&some_struct.opt`, which is type of `&Option`. And we can't suggest `&some_struct.opt?`
+    /// or `(&some_struct.opt)?` since the first one has different semantics and the later does
+    /// not implements `Try`.
+    fn init_expr_can_use_question_mark(cx: &LateContext<'_>, init_expr: &Expr<'_>) -> bool {
+        let init_ty = cx.typeck_results().expr_ty_adjusted(init_expr);
+        cx.tcx
+            .lang_items()
+            .try_trait()
+            .map_or(false, |did| implements_trait(cx, init_ty, did, &[]))
+    }
+
     if let StmtKind::Let(Local {
         pat,
         init: Some(init_expr),
         els: Some(els),
         ..
     }) = stmt.kind
+        && init_expr_can_use_question_mark(cx, init_expr)
         && let Some(ret) = find_let_else_ret_expression(els)
         && let Some(inner_pat) = pat_and_expr_can_be_question_mark(cx, pat, ret)
         && !span_contains_comment(cx.tcx.sess.source_map(), els.span)

tests/ui/question_mark.fixed

@@ -283,3 +283,37 @@ fn issue12337() -> Option<i32> {
     };
     Some(42)
 }
+
+fn issue11983(option: &Option<String>) -> Option<()> {
+    // Don't lint, `&Option` dose not impl `Try`.
+    let Some(v) = option else { return None };
+
+    let opt = Some(String::new());
+    // Don't lint, `branch` method in `Try` takes ownership of `opt`,
+    // and `(&opt)?` also doesn't work since it's `&Option`.
+    let Some(v) = &opt else { return None };
+    let mov = opt;
+
+    Some(())
+}
+
+struct Foo {
+    owned: Option<String>,
+}
+struct Bar {
+    foo: Foo,
+}
+#[allow(clippy::disallowed_names)]
+fn issue12412(foo: &Foo, bar: &Bar) -> Option<()> {
+    // Don't lint, `owned` is behind a shared reference.
+    let Some(v) = &foo.owned else {
+        return None;
+    };
+    // Don't lint, `owned` is behind a shared reference.
+    let Some(v) = &bar.foo.owned else {
+        return None;
+    };
+    // lint
+    let v = bar.foo.owned.clone()?;
+    Some(())
+}

tests/ui/question_mark.rs

@@ -323,3 +323,39 @@ fn issue12337() -> Option<i32> {
     };
     Some(42)
 }
+
+fn issue11983(option: &Option<String>) -> Option<()> {
+    // Don't lint, `&Option` dose not impl `Try`.
+    let Some(v) = option else { return None };
+
+    let opt = Some(String::new());
+    // Don't lint, `branch` method in `Try` takes ownership of `opt`,
+    // and `(&opt)?` also doesn't work since it's `&Option`.
+    let Some(v) = &opt else { return None };
+    let mov = opt;
+
+    Some(())
+}
+
+struct Foo {
+    owned: Option<String>,
+}
+struct Bar {
+    foo: Foo,
+}
+#[allow(clippy::disallowed_names)]
+fn issue12412(foo: &Foo, bar: &Bar) -> Option<()> {
+    // Don't lint, `owned` is behind a shared reference.
+    let Some(v) = &foo.owned else {
+        return None;
+    };
+    // Don't lint, `owned` is behind a shared reference.
+    let Some(v) = &bar.foo.owned else {
+        return None;
+    };
+    // lint
+    let Some(v) = bar.foo.owned.clone() else {
+        return None;
+    };
+    Some(())
+}

tests/ui/question_mark.stderr

@@ -141,5 +141,13 @@ LL | |                 // https://github.com/rust-lang/rust-clippy/pull/11001#is
 LL | |             }
    | |_____________^ help: replace it with: `a?;`
 
-error: aborting due to 16 previous errors
+error: this `let...else` may be rewritten with the `?` operator
+  --> tests/ui/question_mark.rs:357:5
+   |
+LL | /     let Some(v) = bar.foo.owned.clone() else {
+LL | |         return None;
+LL | |     };
+   | |______^ help: replace it with: `let v = bar.foo.owned.clone()?;`
+
+error: aborting due to 17 previous errors