clippy_lints/src/question_mark.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::higher;
   3 use clippy_utils::is_lang_ctor;
   4 use clippy_utils::source::snippet_with_applicability;
   5 use clippy_utils::sugg::Sugg;
   6 use clippy_utils::ty::is_type_diagnostic_item;
   7 use clippy_utils::{eq_expr_value, path_to_local, path_to_local_id};
   8 use if_chain::if_chain;
   9 use rustc_errors::Applicability;
  10 use rustc_hir::LangItem::{OptionNone, OptionSome, ResultOk};
  11 use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, PatKind, StmtKind};
  12 use rustc_lint::{LateContext, LateLintPass};
  13 use rustc_session::{declare_lint_pass, declare_tool_lint};
  14 use rustc_span::sym;
  15
  16 declare_clippy_lint! {
  17     /// ### What it does
  18     /// Checks for expressions that could be replaced by the question mark operator.
  19     ///
  20     /// ### Why is this bad?
  21     /// Question mark usage is more idiomatic.
  22     ///
  23     /// ### Example
  24     /// ```ignore
  25     /// if option.is_none() {
  26     ///     return None;
  27     /// }
  28     /// ```
  29     ///
  30     /// Could be written:
  31     ///
  32     /// ```ignore
  33     /// option?;
  34     /// ```
  35     #[clippy::version = "pre 1.29.0"]
  36     pub QUESTION_MARK,
  37     style,
  38     "checks for expressions that could be replaced by the question mark operator"
  39 }
  40
  41 declare_lint_pass!(QuestionMark => [QUESTION_MARK]);
  42
  43 impl QuestionMark {
  44     /// Checks if the given expression on the given context matches the following structure:
  45     ///
  46     /// ```ignore
  47     /// if option.is_none() {
  48     ///    return None;
  49     /// }
  50     /// ```
  51     ///
  52     /// ```ignore
  53     /// if result.is_err() {
  54     ///     return result;
  55     /// }
  56     /// ```
  57     ///
  58     /// If it matches, it will suggest to use the question mark operator instead
  59     fn check_is_none_or_err_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>) {
  60         if_chain! {
  61             if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
  62             if let ExprKind::MethodCall(segment, _, args, _) = &cond.kind;
  63             if let Some(subject) = args.get(0);
  64             if (Self::option_check_and_early_return(cx, subject, then) && segment.ident.name == sym!(is_none)) ||
  65                 (Self::result_check_and_early_return(cx, subject, then) && segment.ident.name == sym!(is_err));
  66             then {
  67                 let mut applicability = Applicability::MachineApplicable;
  68                 let receiver_str = &Sugg::hir_with_applicability(cx, subject, "..", &mut applicability);
  69                 let mut replacement: Option<String> = None;
  70                 if let Some(else_inner) = r#else {
  71                     if_chain! {
  72                         if let ExprKind::Block(block, None) = &else_inner.kind;
  73                         if block.stmts.is_empty();
  74                         if let Some(block_expr) = &block.expr;
  75                         if eq_expr_value(cx, subject, block_expr);
  76                         then {
  77                             replacement = Some(format!("Some({}?)", receiver_str));
  78                         }
  79                     }
  80                 } else if Self::moves_by_default(cx, subject)
  81                     && !matches!(subject.kind, ExprKind::Call(..) | ExprKind::MethodCall(..))
  82                 {
  83                     replacement = Some(format!("{}.as_ref()?;", receiver_str));
  84                 } else {
  85                     replacement = Some(format!("{}?;", receiver_str));
  86                 }
  87
  88                 if let Some(replacement_str) = replacement {
  89                     span_lint_and_sugg(
  90                         cx,
  91                         QUESTION_MARK,
  92                         expr.span,
  93                         "this block may be rewritten with the `?` operator",
  94                         "replace it with",
  95                         replacement_str,
  96                         applicability,
  97                     );
  98                 }
  99             }
 100         }
 101     }
 102
 103     fn check_if_let_some_or_err_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>) {
 104         if_chain! {
 105             if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: Some(if_else) })
 106                 = higher::IfLet::hir(cx, expr);
 107             if let PatKind::TupleStruct(ref path1, fields, None) = let_pat.kind;
 108             if (Self::option_check_and_early_return(cx, let_expr, if_else) && is_lang_ctor(cx, path1, OptionSome)) ||
 109                 (Self::result_check_and_early_return(cx, let_expr, if_else) && is_lang_ctor(cx, path1, ResultOk));
 110
 111             if let PatKind::Binding(annot, bind_id, _, _) = fields[0].kind;
 112             let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
 113             if let ExprKind::Block(block, None) = if_then.kind;
 114             if block.stmts.is_empty();
 115             if let Some(trailing_expr) = &block.expr;
 116             if path_to_local_id(trailing_expr, bind_id);
 117             then {
 118                 let mut applicability = Applicability::MachineApplicable;
 119                 let receiver_str = snippet_with_applicability(cx, let_expr.span, "..", &mut applicability);
 120                 let replacement = format!("{}{}?", receiver_str, if by_ref { ".as_ref()" } else { "" },);
 121
 122                 span_lint_and_sugg(
 123                     cx,
 124                     QUESTION_MARK,
 125                     expr.span,
 126                     "this if-let-else may be rewritten with the `?` operator",
 127                     "replace it with",
 128                     replacement,
 129                     applicability,
 130                 );
 131             }
 132         }
 133     }
 134
 135     fn result_check_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>, nested_expr: &Expr<'_>) -> bool {
 136         Self::is_result(cx, expr) && Self::expression_returns_unmodified_err(cx, nested_expr, expr)
 137     }
 138
 139     fn option_check_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>, nested_expr: &Expr<'_>) -> bool {
 140         Self::is_option(cx, expr) && Self::expression_returns_none(cx, nested_expr)
 141     }
 142
 143     fn moves_by_default(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 144         let expr_ty = cx.typeck_results().expr_ty(expression);
 145
 146         !expr_ty.is_copy_modulo_regions(cx.tcx.at(expression.span), cx.param_env)
 147     }
 148
 149     fn is_option(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 150         let expr_ty = cx.typeck_results().expr_ty(expression);
 151
 152         is_type_diagnostic_item(cx, expr_ty, sym::Option)
 153     }
 154
 155     fn is_result(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 156         let expr_ty = cx.typeck_results().expr_ty(expression);
 157
 158         is_type_diagnostic_item(cx, expr_ty, sym::Result)
 159     }
 160
 161     fn expression_returns_none(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
 162         match expression.kind {
 163             ExprKind::Block(block, _) => {
 164                 if let Some(return_expression) = Self::return_expression(block) {
 165                     return Self::expression_returns_none(cx, return_expression);
 166                 }
 167
 168                 false
 169             },
 170             ExprKind::Ret(Some(expr)) => Self::expression_returns_none(cx, expr),
 171             ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
 172             _ => false,
 173         }
 174     }
 175
 176     fn expression_returns_unmodified_err(cx: &LateContext<'_>, expr: &Expr<'_>, cond_expr: &Expr<'_>) -> bool {
 177         match expr.kind {
 178             ExprKind::Block(block, _) => {
 179                 if let Some(return_expression) = Self::return_expression(block) {
 180                     return Self::expression_returns_unmodified_err(cx, return_expression, cond_expr);
 181                 }
 182
 183                 false
 184             },
 185             ExprKind::Ret(Some(ret_expr)) => Self::expression_returns_unmodified_err(cx, ret_expr, cond_expr),
 186             ExprKind::Path(_) => path_to_local(expr) == path_to_local(cond_expr),
 187             _ => false,
 188         }
 189     }
 190
 191     fn return_expression<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
 192         // Check if last expression is a return statement. Then, return the expression
 193         if_chain! {
 194             if block.stmts.len() == 1;
 195             if let Some(expr) = block.stmts.iter().last();
 196             if let StmtKind::Semi(expr) = expr.kind;
 197             if let ExprKind::Ret(Some(ret_expr)) = expr.kind;
 198
 199             then {
 200                 return Some(ret_expr);
 201             }
 202         }
 203
 204         // Check for `return` without a semicolon.
 205         if_chain! {
 206             if block.stmts.is_empty();
 207             if let Some(ExprKind::Ret(Some(ret_expr))) = block.expr.as_ref().map(|e| &e.kind);
 208             then {
 209                 return Some(ret_expr);
 210             }
 211         }
 212
 213         None
 214     }
 215 }
 216
 217 impl<'tcx> LateLintPass<'tcx> for QuestionMark {
 218     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 219         Self::check_is_none_or_err_and_early_return(cx, expr);
 220         Self::check_if_let_some_or_err_and_early_return(cx, expr);
 221     }
 222 }