clippy_lints/src/question_mark.rs

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