Fix question_mark FP on variables used after (#15644)

Closes #15635

changelog: [`question_mark`] fix FP on variables used after

Author: samueltardieu

clippy_lints/src/question_mark.rs

@@ -6,7 +6,8 @@ use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::msrvs::{self, Msrv};
 use clippy_utils::source::snippet_with_applicability;
 use clippy_utils::sugg::Sugg;
-use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
+use clippy_utils::ty::{implements_trait, is_copy, is_type_diagnostic_item};
+use clippy_utils::usage::local_used_after_expr;
 use clippy_utils::{
     eq_expr_value, fn_def_id_with_node_args, higher, is_else_clause, is_in_const_context, is_lint_allowed,
     is_path_lang_item, is_res_lang_ctor, pat_and_expr_can_be_question_mark, path_res, path_to_local, path_to_local_id,
@@ -483,6 +484,13 @@ fn check_if_let_some_or_err_and_early_return<'tcx>(cx: &LateContext<'tcx>, expr:
             .filter(|e| *e)
             .is_none()
     {
+        if !is_copy(cx, caller_ty)
+            && let Some(hir_id) = path_to_local(let_expr)
+            && local_used_after_expr(cx, hir_id, expr)
+        {
+            return;
+        }
+
         let mut applicability = Applicability::MachineApplicable;
         let receiver_str = snippet_with_applicability(cx, let_expr.span, "..", &mut applicability);
         let requires_semi = matches!(cx.tcx.parent_hir_node(expr.hir_id), Node::Stmt(_));

tests/ui/question_mark.fixed

@@ -475,3 +475,28 @@ fn issue_15679() -> Result<i32, String> {
 
     Ok(0)
 }
+
+mod issue14894 {
+    fn use_after_question_mark(do_something_else: impl Fn() -> Result<String, ()>) -> Result<(), ()> {
+        let result = do_something_else();
+        if let Err(reason) = result {
+            return Err(reason);
+        }
+        drop(result);
+
+        let result = do_something_else();
+        let x = result?;
+        drop(x);
+
+        Ok(())
+    }
+
+    #[expect(dropping_copy_types)]
+    fn use_after_question_mark_but_is_copy(do_something_else: impl Fn() -> Result<i32, ()>) -> Result<(), ()> {
+        let result = do_something_else();
+        result?;
+        drop(result);
+
+        Ok(())
+    }
+}

tests/ui/question_mark.rs

@@ -583,3 +583,35 @@ fn issue_15679() -> Result<i32, String> {
 
     Ok(0)
 }
+
+mod issue14894 {
+    fn use_after_question_mark(do_something_else: impl Fn() -> Result<String, ()>) -> Result<(), ()> {
+        let result = do_something_else();
+        if let Err(reason) = result {
+            return Err(reason);
+        }
+        drop(result);
+
+        let result = do_something_else();
+        let x = match result {
+            //~^ question_mark
+            Ok(v) => v,
+            Err(e) => return Err(e),
+        };
+        drop(x);
+
+        Ok(())
+    }
+
+    #[expect(dropping_copy_types)]
+    fn use_after_question_mark_but_is_copy(do_something_else: impl Fn() -> Result<i32, ()>) -> Result<(), ()> {
+        let result = do_something_else();
+        if let Err(reason) = result {
+            //~^ question_mark
+            return Err(reason);
+        }
+        drop(result);
+
+        Ok(())
+    }
+}

tests/ui/question_mark.stderr

@@ -313,5 +313,25 @@ LL | |         Err(err) => return Err(<&str as Into<String>>::into(err)),
 LL | |     };
    | |_____^ help: try instead: `some_result?`
 
-error: aborting due to 33 previous errors
+error: this `match` expression can be replaced with `?`
+  --> tests/ui/question_mark.rs:596:17
+   |
+LL |           let x = match result {
+   |  _________________^
+LL | |
+LL | |             Ok(v) => v,
+LL | |             Err(e) => return Err(e),
+LL | |         };
+   | |_________^ help: try instead: `result?`
+
+error: this block may be rewritten with the `?` operator
+  --> tests/ui/question_mark.rs:609:9
+   |
+LL | /         if let Err(reason) = result {
+LL | |
+LL | |             return Err(reason);
+LL | |         }
+   | |_________^ help: replace it with: `result?;`
+
+error: aborting due to 35 previous errors