src/tools/clippy/clippy_lints/src/question_mark.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::higher;
   3 use clippy_utils::source::snippet_with_applicability;
   4 use clippy_utils::sugg::Sugg;
   5 use clippy_utils::ty::is_type_diagnostic_item;
   6 use clippy_utils::{eq_expr_value, is_lang_ctor, path_to_local, path_to_local_id, peel_blocks, peel_blocks_with_stmt};
   7 use if_chain::if_chain;
   8 use rustc_errors::Applicability;
   9 use rustc_hir::LangItem::{OptionNone, OptionSome, ResultOk};
  10 use rustc_hir::{BindingAnnotation, Expr, ExprKind, PatKind};
  11 use rustc_lint::{LateContext, LateLintPass};
  12 use rustc_session::{declare_lint_pass, declare_tool_lint};
  13 use rustc_span::sym;
  14
  15 declare_clippy_lint! {
  16     /// ### What it does
  17     /// Checks for expressions that could be replaced by the question mark operator.
  18     ///
  19     /// ### Why is this bad?
  20     /// Question mark usage is more idiomatic.
  21     ///
  22     /// ### Example
  23     /// ```ignore
  24     /// if option.is_none() {
  25     ///     return None;
  26     /// }
  27     /// ```
  28     ///
  29     /// Could be written:
  30     ///
  31     /// ```ignore
  32     /// option?;
  33     /// ```
  34     #[clippy::version = "pre 1.29.0"]
  35     pub QUESTION_MARK,
  36     style,
  37     "checks for expressions that could be replaced by the question mark operator"
  38 }
  39
  40 declare_lint_pass!(QuestionMark => [QUESTION_MARK]);
  41
  42 impl QuestionMark {
  43     /// Checks if the given expression on the given context matches the following structure:
  44     ///
  45     /// ```ignore
  46     /// if option.is_none() {
  47     ///    return None;
  48     /// }
  49     /// ```
  50     ///
  51     /// ```ignore
  52     /// if result.is_err() {
  53     ///     return result;
  54     /// }
  55     /// ```
  56     ///
  57     /// If it matches, it will suggest to use the question mark operator instead
  58     fn check_is_none_or_err_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>) {
  59         if_chain! {
  60             if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
  61             if let ExprKind::MethodCall(segment, args, _) = &cond.kind;
  62             if let Some(subject) = args.get(0);
  63             if (Self::option_check_and_early_return(cx, subject, then) && segment.ident.name == sym!(is_none)) ||
  64                 (Self::result_check_and_early_return(cx, subject, then) && segment.ident.name == sym!(is_err));
  65             then {
  66                 let mut applicability = Applicability::MachineApplicable;
  67                 let receiver_str = &Sugg::hir_with_applicability(cx, subject, "..", &mut applicability);
  68                 let mut replacement: Option<String> = None;
  69                 if let Some(else_inner) = r#else {
  70                     if eq_expr_value(cx, subject, peel_blocks(else_inner)) {
  71                         replacement = Some(format!("Some({}?)", receiver_str));
  72                     }
  73                 } else if Self::moves_by_default(cx, subject)
  74                     && !matches!(subject.kind, ExprKind::Call(..) | ExprKind::MethodCall(..))
  75                 {
  76                     replacement = Some(format!("{}.as_ref()?;", receiver_str));
  77                 } else {
  78                     replacement = Some(format!("{}?;", receiver_str));
  79                 }
  80
  81                 if let Some(replacement_str) = replacement {
  82                     span_lint_and_sugg(
  83                         cx,
  84                         QUESTION_MARK,
  85                         expr.span,
  86                         "this block may be rewritten with the `?` operator",
  87                         "replace it with",
  88                         replacement_str,
  89                         applicability,
  90                     );
  91                 }
  92             }
  93         }
  94     }
  95
  96     fn check_if_let_some_or_err_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>) {
  97         if_chain! {
  98             if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: Some(if_else) })
  99                 = higher::IfLet::hir(cx, expr);
 100             if let PatKind::TupleStruct(ref path1, fields, None) = let_pat.kind;
 101             if (Self::option_check_and_early_return(cx, let_expr, if_else) && is_lang_ctor(cx, path1, OptionSome)) ||
 102                 (Self::result_check_and_early_return(cx, let_expr, if_else) && is_lang_ctor(cx, path1, ResultOk));
 103
 104             if let PatKind::Binding(annot, bind_id, _, _) = fields[0].kind;
 105             let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
 106             if path_to_local_id(peel_blocks(if_then), bind_id);
 107             then {
 108                 let mut applicability = Applicability::MachineApplicable;
 109                 let receiver_str = snippet_with_applicability(cx, let_expr.span, "..", &mut applicability);
 110                 let replacement = format!("{}{}?", receiver_str, if by_ref { ".as_ref()" } else { "" },);
 111
 112                 span_lint_and_sugg(
 113                     cx,
 114                     QUESTION_MARK,
 115                     expr.span,
 116                     "this if-let-else may be rewritten with the `?` operator",
 117                     "replace it with",
 118                     replacement,
 119                     applicability,
 120                 );
 121             }
 122         }
 123     }
 124
 125     fn result_check_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>, nested_expr: &Expr<'_>) -> bool {
 126         Self::is_result(cx, expr) && Self::expression_returns_unmodified_err(cx, nested_expr, expr)
 127     }
 128
 129     fn option_check_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>, nested_expr: &Expr<'_>) -> bool {
 130         Self::is_option(cx, expr) && Self::expression_returns_none(cx, nested_expr)
 131     }
 132
 133     fn moves_by_default(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 134         let expr_ty = cx.typeck_results().expr_ty(expression);
 135
 136         !expr_ty.is_copy_modulo_regions(cx.tcx.at(expression.span), cx.param_env)
 137     }
 138
 139     fn is_option(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 140         let expr_ty = cx.typeck_results().expr_ty(expression);
 141
 142         is_type_diagnostic_item(cx, expr_ty, sym::Option)
 143     }
 144
 145     fn is_result(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 146         let expr_ty = cx.typeck_results().expr_ty(expression);
 147
 148         is_type_diagnostic_item(cx, expr_ty, sym::Result)
 149     }
 150
 151     fn expression_returns_none(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 152         match peel_blocks_with_stmt(expression).kind {
 153             ExprKind::Ret(Some(expr)) => Self::expression_returns_none(cx, expr),
 154             ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
 155             _ => false,
 156         }
 157     }
 158
 159     fn expression_returns_unmodified_err(cx: &LateContext<'_>, expr: &Expr<'_>, cond_expr: &Expr<'_>) -> bool {
 160         match peel_blocks_with_stmt(expr).kind {
 161             ExprKind::Ret(Some(ret_expr)) => Self::expression_returns_unmodified_err(cx, ret_expr, cond_expr),
 162             ExprKind::Path(_) => path_to_local(expr).is_some() && path_to_local(expr) == path_to_local(cond_expr),
 163             _ => false,
 164         }
 165     }
 166 }
 167
 168 impl<'tcx> LateLintPass<'tcx> for QuestionMark {
 169     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 170         Self::check_is_none_or_err_and_early_return(cx, expr);
 171         Self::check_if_let_some_or_err_and_early_return(cx, expr);
 172     }
 173 }